Oil and Gas Terms Beginning with “P”

To prepare a well to be closed permanently, usually after either logs determine there is insufficient hydrocarbon potential to complete the well, or after production operations have drained the reservoir. Different regulatory bodies have their own requirements for plugging operations. Most require that cement plugs be placed and tested across any open hydrocarbon-bearing formations, across all casing shoes, across freshwater aquifers, and perhaps several other areas near the surface, including the top 20 to 50 ft [6 to 15 m] of the wellbore. The well designer may choose to set bridge plugs in conjunction with cement slurries to ensure that higher density cement does not fall in the wellbore. In that case, the bridge plug would be set and cement pumped on top of the plug through drillpipe, and then the drillpipe withdrawn before the slurry thickened.

An elastic body wave or sound wave in which particles oscillate in the direction the wave propagates. P-waves are the waves studied in conventional seismic data. P-waves incident on an interface at other than normal incidence can produce reflected and transmitted S-waves, in that case known as converted waves.

A cellulose derivative similar in structure, properties and usage in drilling fluids to carboxymethylcellulose. PAC is considered to be a premium product because it typically has a higher degree of carboxymethyl substitution and contains less residual NaCl than technical grade carboxymethylcellulose, although some PACs contain considerable NaCl.

A polymer or copolymer of an alkalene oxide, such as polyethylene glycol (PEG), a polymer of ethylene oxide with general formula HO(CH2CH2O)nH, or polypropylene glycol (PPG), which is a polymer of propylene oxide. PAGs are effective shale inhibitors and have effectively replaced the earlier polyglycerols.

One of the synthetic hydrocarbon liquids manufactured from the monomer ethylene, H2C=CH2. Polyalphaolefins have a complex branched structure with an olefin bond in the alpha position of one of the branches. Hydrogenated polyalphaolefins have olefin-carbons saturated with hydrogen, which lends excellent thermal stability to the molecule. Synthetic-base fluids (similar to oil muds) are made with the various types of synthetic liquids because the cuttings can be discharged in offshore waters, whereas discharge of cuttings coated with refined oils would be disallowed.

The Oslo and Paris Commission, formerly known as PARCOM. The commission is a group of experts who advise North Sea countries on environmental policy and legislation. OSPAR has been influential in establishing North Sea legislation on drilling fluids that has served as the model for other operating areas. OSPAR has published lists of environmentally acceptable and unacceptable products, referred to as the "green," "grey" and "black" lists. The Green or A list consists of products posing relatively little harm to the environment (specifically the marine environment). Examples include inert minerals such as bentonite, inorganic salts that are common constituents of seawater such as sodium and potassium chloride, and simple organic products such as starch and carboxymethylcellulose (CMC). The Grey List consists of products 'requiring strong regulatory control' and includes heavy metals such as zinc, lead and chromium. The Black list covers products considered unsuitable for discharge and includes mercury, cadmium and 'persistent oils and hydrocarbons of a petroleum origin.' The inclusion of hydrocarbons in the black list has been the driving force behind the reduction of oil discharges in the North Sea and elsewhere and has serious implications for the use of oil and synthetic fluids.

A drilling tool that uses polycrystalline diamond compact (PDC) cutters to shear rock with a continuous scraping motion. These cutters are synthetic diamond disks about 1/8-in. thick and about 1/2 to 1 in. in diameter. PDC bits are effective at drilling shale formations, especially when used in combination with oil-base muds.

A log of photoelectric absorption properties. The log measures the photoelectric absorption factor, Pe, which is defined as (Z/10) 3.6 where Z is the average atomic number of the formation. Pe is unitless, but since it is proportional to the photoelectric cross section per electron, it is sometimes quoted in barns/electron. Since fluids have very low atomic numbers, they have very little influence, so that Pe is a measure of the rockmatrix properties. Sandstones have low Pe, while dolomites and limestones have high Pe. Clays, heavy minerals and iron-bearing minerals have high Pe. Thus, the log is very useful for determining mineralogy. In interpretation, PEF is normally converted to the simpler volumetric cross section, U in barns/cm3, by taking the product of PEF and density.The log is recorded as part of the density measurement. The depth of investigation is of the order of one inch, which is normally in the flushed zone. PEF can be affected by heavy minerals such as barite in the mudcake or mud filtrate. PEF logs were introduced in the late 1970s.

A class of water muds that use partially-hydrolyzed polyacrylamide (PHPA) as a functional additive, either to control wellbore shales or to extend bentoniteclay in a low-solids mud. As a shale-control mud, PHPA is believed to seal microfractures and coat shale surfaces with a film that retards dispersion and disintegration. KCl is used as a shale inhibitor in most PHPA mud designs. In low-solids muds, PHPA interacts with minimal concentrations of bentonite to link particles together and improve rheology without increased colloidal solids loading.Reference:Clark RK, Scheuerman RF, Raoth H and van Laar H: "Polyacrylamide-Potassium Chloride Mud for Drilling Water Sensitive Shales," Journal of Petroleum Technology 28, no. 6 (June 1976): 719-726.Reference:Fraser LJ: "New Method Accurately Analyzes PHPA's in Muds," Oil & Gas Journal 85, no. 27 (July 6, 1987): 39-42.

A class of water muds that use partially-hydrolyzed polyacrylamide (PHPA) as a functional additive, either to control wellbore shales or to extend bentoniteclay in a low-solids mud. As a shale-control mud, PHPA is believed to seal microfractures and coat shale surfaces with a film that retards dispersion and disintegration. KCl is used as a shale inhibitor in most PHPA mud designs. In low-solids muds, PHPA interacts with minimal concentrations of bentonite to link particles together and improve rheology without increased colloidal solids loading.Reference:Clark RK, Scheuerman RF, Raoth H and van Laar H: "Polyacrylamide-Potassium Chloride Mud for Drilling Water Sensitive Shales," Journal of Petroleum Technology 28, no. 6 (June 1976): 719-726.Reference:Fraser LJ: "New Method Accurately Analyzes PHPA's in Muds," Oil & Gas Journal 85, no. 27 (July 6, 1987): 39-42.

Abbreviation for productivity index.

Abbreviation for ProductionLogging Tool.

A solvent used with water to break the emulsion of an oil-base or synthetic-base drilling fluid to prepare the sample for chemical titrations to determine lime, calcium or chloride content according to API testing procedures. PNP is an abbreviation for propylene glycolnormal propyl ether. It is an environmentally friendlier replacement of a xylene-isopropynol mixture previously used in certain titrations.

A term used to describe the beginning of thickening of a cementslurry during the thickening-time test, often abbreviated as POD. For some slurries, the POD is used as the thickening time.

A specialized apparatus used in the particle-plugging test. The PPA is used to determine the ability of particles in the drilling fluid to effectively bridge the pores in the filtermedium and, therefore, the ability of the mud to reduce formation damage in the reservoir. The apparatus resembles a high-pressure, high-temperature filtration cell that has been modified to operate upside down (to remove the effects of gravity) and to accept filter media of different permeabilities (sintered metal, which is chosen for higher temperature conditions, aloxite, which is a porous ceramic material, or rock). The medium is selected to match the permeability of the reservoir to be drilled. The filter medium is at the top so that sediment will not affect the filter cake. Pressure is applied hydraulically from below.

A laboratory test used to determine if a drilling fluid blocks movement of filtrate through pore spaces of a shale sample. The PPT device monitors the increase in pore pressure in a shale when exposed to a drilling fluid over a period of time. Shale cores from 1 to 3-inches long are fitted into a modified Hassler cell that has sensitive pressure transducers in reservoirs on each end of the cell.Reference:van Oort E, Hale AH, Mody FK and Roy S: "Transport in Shales and the Design of Improved Water-Based Shale Drilling Fluids," in SPE Drilling and Completion 11, no. 3 (September 1996): 137-146

A mnemonic for the pseudostatic spontaneous potential.

A parameter of the Bingham plasticmodel. PV is the slope of the shearstress/shear rate line above the yield point. PV represents the viscosity of a mud when extrapolated to infinite shear rate on the basis of the mathematics of the Bingham model. (Yield point, YP, is the other parameter of that model.) A low PV indicates that the mud is capable of drilling rapidly because of the low viscosity of mud exiting at the bit. High PV is caused by a viscous base fluid and by excess colloidal solids. To lower PV, a reduction in solids content can be achieved by dilution of the mud.

A shorthand term for pressure, volume, temperature dependencies for fluid properties. In oil-base drilling fluids, PVT effects on viscosity and density must be understood to develop density and hydraulics programs. Downhole pressure makes the base oil more viscous and dense, whereas temperature has the opposite effect. Brines for downhole use also require an understanding of PVT behavior.

Protective clothing or equipment designed to protect the wearer from job-related hazards. Minimum required: hardhat, safety glasses, fire retardant coveralls, and steel-toed boots. Also known as PPE.

A chemical property of an aqueous system that implies that there are more hydroxyl ions (OH-) in the system, or a potential to produce more hydroxyl ions, than there are hydrogen ions (H+), or potential to produce hydrogen ions.

A double logarithmic plot of a resistivity measurement on the x-axis versus a porosity measurement on the y-axis. The plot is named after G.R. Pickett. The plot is based on taking the logarithm of the Archie equation. Points of constant water saturation (Sw) will plot on a straight line with negative slope of value m. Water zones define the lowermost line on the plot. Since Sw = 1, the water resistivity can be determined from a point on the line. Once the water line is established, other parallel lines can be drawn for different Sw, assuming a constant n (usually 2). Other data can then be plotted and interpreted in terms of Sw. The same technique can be applied to the flushed zone, using flushed-zone measurements.See Pickett GR: "A Review of Current Techniques for Determination of Water Saturation from Logs," paper SPE 1446, presented at the SPE Rocky Mountain Regional Meeting, Denver, Colorado, USA, May 23-24, 1966; SPE Journal of Petroleum Technology (November 1966): 1425-1435.

A hydraulic or pneumatic wrench used to make up or break out drill pipe, tubing, or casing on which the torque is provided by air or fluid pressure.

A measuring device for determining the gas-flow rate. It is composed of a 1/8-inch tube inserted horizontally along the axis of the gas flowline. The pressure at the end of the tube is compared with the static pressure to determine the final gas flow rate within the flow line.

A chemical property of an aqueous system that implies that there are more hydroxyl ions (OH-) in the system, or a potential to produce more hydroxyl ions, than there are hydrogen ions (H+), or potential to produce hydrogen ions.

A probabilitydistribution in which the mean and the variance are identical. This distribution was first described by S.D. Poisson, a French mathematician and physicist (1781-1840).

An elastic constant that is a measure of the compressibility of material perpendicular to applied stress, or the ratio of latitudinal to longitudinal strain. This elastic constant is named for Simeon Poisson (1781 to 1840), a French mathematician. Poisson's ratio can be expressed in terms of properties that can be measured in the field, including velocities of P-waves and S-waves as shown below.Note that if VS = 0, then Poisson's ratio equals 1/2, indicating either a fluid, because shear waves do not pass through fluids, or a material that maintains constant volume regardless of stress, also known as an ideal incompressible material. VS approaching zero is characteristic of a gas reservoir. Poisson's ratio for carbonate rocks is ~ 0.3, for sandstones ~0.2, and above 0.3 for shale. The Poisson's ratio of coal is ~ 0.4.

An air or inert gas device that minimizes pressure surges in the output line of a mud pump. Also called a surge dampener.

Slang for penetration rate, or the speed that the bit is drilling into the formation.

Slang for penetration rate, or the speed that the bit is drilling into the formation.

Hydrogen ion potential, which is the log10 of the reciprocal of hydrogen ion, H+, concentration. Mathematically, pH = log10 (1/[H+]), where [ ] represents mole/L. pH is derived from the ion-product constant of water, which at room temperature is 1 x 10-14 = [H+] x [OH-]. Pure water (at neutral pH) has equal concentrations of its two ions: [H+] = [OH-] = 10-7 mole/L. Log10 1/[H+] is 7, which is the pH of a neutral solution. The pH scale ranges from 0 to 14, and values below 7 are acidic and above 7 are basic.

A drilling-fluid test to measure pH of muds and mud filtrates, usually performed according to API specifications. The pH test uses a pH meter equipped with a glass-membrane measuring electrode and reference electrode, which read from 0 to 14. The preferred pH meter automatically compensates for temperature. Buffer solutions of pH = 4, 7 and 10 are specified for calibration of the meter. Color-matching pH paper and sticks are not recommended except for simple muds.

To effect hydraulic isolation, either with a sealing device, such as a packer, or with a specialized plastic or fluid, such as a sealing compound.

A downhole device used in almost every completion to isolate the annulus from the production conduit, enabling controlled production, injection or treatment. A typical packer assembly incorporates a means of securing the packer against the casing or liner wall, such as a slip arrangement, and a means of creating a reliable hydraulic seal to isolate the annulus, typically by means of an expandable elastomeric element. Packers are classified by application, setting method and possible retrievability.

A device for measuring in situ the velocity of fluid flow in a production or injection well in which a packer is inflated between the tool housing and the casing wall, causing the total fluid flow to pass inside the tool and over a spinner. The measurement is made with the tool stationary, after borehole fluids have been pumped to inflate the packer. The packer flowmeter was introduced in the mid-1950s. It is a type of diverter flowmeter, but has generally been replaced by petal basket and inflatable diverter flowmeters.

The fluid that remains in the tubing-casingannulus above the packer after the completion has been run and all circulation devices have been isolated. Packer fluids are prepared for the requirements of the given completion. Generally, they should be of sufficient density to control the producing formation, be solids-free and resistant to viscosity changes over long periods of time, and be noncorrosive to the wellbore and completion components.

A device used to seal around a reciprocating or rotating shaft or spindle. A malleable packing compound is forced into place by an adjustable packing nut, or similar arrangement. This enables the seal or packing to be tightened to suit the operating conditions and allows subsequent adjustment to account for wear.

To effect hydraulic isolation, either with a sealing device, such as a packer, or with a specialized plastic or fluid, such as a sealing compound.

That part of a wireline logging tool that is pressed firmly against the borehole wall. The pad holds sensors that are focused in one direction and must be as close as possible to the borehole wall. The density detectors and the microresistivity electrodes are examples of sensors that must be placed on pads. Some pads are a rigid part of the logging tool. Others have articulated joints attaching them to the logging tool, with a backup arm to press the pad against the borehole wall.

A type of fluid-mixing tank used in the preparation of treatment fluids or slurries that provides the agitation to achieve a well-dispersed mixture. Paddle mixers are generally equipped with rotating paddles that provide turbulence for mixing fluids and an action that prevents the settling of solids prior to being pumped.

An oil and gas lease in which delay rentals for the entire primary term are paid in advance with the bonus consideration.

A gamma ray interaction in which the gamma ray, or photon, is converted into an electron and a positron when the gamma ray enters the strong electric field near the nucleus of an atom. The gamma ray energy must equal at least the rest mass of an electron and a positron (1.022 MeV) for the interaction to be possible. Following pair production, the positron will annihilate with an electron, emitting two gamma rays of 0.511 MeV. The highest probability of occurrence is at high gamma ray energy, above 10 MeV, and in a material of high atomic number.

The study of fossilized, or preserved, remnants of plant and animal life. Changes in the Earth through time can be documented by observing changes in the fossils in successive strata and the environments in which they formed or were preserved. Fossils can also be compared with their extant relatives to assess evolutionary changes. Correlations of strata can be aided by studying their fossil content, a discipline called biostratigraphy.

Pertaining to a depositional environment or organisms from a marsh. It also refers to the type of environment in which palustrine sediments can accumulate.

Describing material deposited in or growing in a marsh.

The study of fossilized remnants of microscopic entities having organic walls, such as pollen, spores and cysts from algae. Changes in the Earth through time can be documented by studying the distribution of spores and pollen. Well log and other correlations are enhanced by incorporating palynology. Palynology also has utility in forensics.

A hydrocarbon compound that often precipitates on production components as a result of the changing temperatures and pressures within the production system. Heavy paraffins occur as wax-like substances that may build up on the completion components and may, if severe, restrict production.Paraffin is normally found in the tubing close to surface. Nevertheless, it can form at the perforations, or even inside the formation, especially in depleted reservoirs or reservoirs under gas-cycling conditions.

A set of techniques used to prevent or considerably reduce paraffin deposition. Paraffin control might involve the following options:· use of paraffin inhibitors.· maintaining pipe surfaces in a water-wet condition because paraffin will not adhere to water. However, the presence of natural surfactants in some crude oils converts water-wet surfaces to an oil-wet condition, making this technique effective only temporarily.· coating the pipe with plastic to provide a smooth surface and reduce paraffin adhesion.· reducing heat transfer to maintain the oil temperature above its cloud point. Filling the annulus of a well with a fluid that has poorer heat transfer properties than the oil maintains the temperature of the flowing crude oil above its cloud point.

A chemical injected into the wellbore to prevent or minimize paraffin deposition. The effectiveness of paraffin inhibitors is strongly dependent on crude oil composition.Paraffin inhibitors must be introduced into the oil before the oil cools to its cloud point. In additional, asphaltene composition should be determined before treatment because it can reduce the effectiveness of the paraffin inhibitor. In some cases, the use of a paraffin inhibitor can actually increase the rate of paraffin deposition because the stability of colloidalasphaltenes is disturbed.

(noun) A mechanical tool run on wireline, slickline, or sucker rods inside the production tubing to remove accumulated paraffin wax deposits from the inner wall, restoring the full bore diameter and maintaining production flow rates in wells susceptible to wax deposition.

A downhole tool, generally run on slickline, used to remove paraffin and soft wax deposits from the internal wall of productiontubulars and completion equipment.

A crude oil containing paraffin wax but very few asphaltic materials. This type of oil is suitable for motor lubricating oil and kerosene.

The group of hydrocarbons consisting of linear molecules with the formula CnH2n+2. Methane, CH4, is the simplest member. Higher members, starting at about C18, are wax-like and are called paraffin. Excessive amounts of paraffinic hydrocarbons in an oil mud adversely affect mud flow and oil removal from cuttings at cool temperatures.

A commonly used preservative for starch, xanthan gum, guar gum and other natural polymers that are prone to attack by bacteria. It is as a trimer of formaldehyde and has the formula O-CH2-O-CH2-O-CH2. Paraformaldehyde is a white, water soluble powder. When added to a mud in advance of a bacterial inoculation and maintained, paraformaldehyde can effectively control many strains of bacteria. The amount or paraformaldehyde in a mud can be estimated by oxidizing it with sulfite into formic acid and performing an alkalinitytitration, according to a procedure published by API.

The deformation of rock layers in which the thickness of each layer, measured perpendicular to initial (undeformed) layering, is maintained after the rock layers have been folded.

The resistivity of a formation measured by flowing current parallel to the bedding planes. In anisotropic formations, the parallel and perpendicular resistivities are different.

A variable that is given a constant value for the purposes of certain calculations. For example, during log analysis of a particular layer of a reservoir, the water resistivity (Rw) may be set to a particular value and referred to as a parameter.

Pertaining to a method of seismic inversion to separate wavefields by iteratively developing a model of the data that conforms to the recorded data. Parametric inversion is used in processing vertical seismic profile (VSP) data.

Relatively conformable depositional units bounded by surfaces of marine flooding, surfaces that separate older strata from younger and show an increase in water depth in successively younger strata. Parasequences are usually too thin to discern on seismic data, but when added together, they form sets called parasequence sets that are visible on seismic data.

A marine flooding surface or its correlative surface.

A succession of genetically related parasequences that form a distinctive stacking pattern, and that are typically bounded by major marine flooding surfaces and their correlative surfaces. Parasequence sets are usually classified as progradational, aggradational or retrogradational.

Completion of or flow from less than the entire producing interval. This situation causes a near-well flow constriction that results in a positive skin effect in a well-test analysis.

An incompletely drilled portion of the productive interval.

The proportion of exploration and production costs each party will bear and the proportion of production each party will receive, as set out in an operating agreement.

A specialized apparatus used in the particle-plugging test. The PPA is used to determine the ability of particles in the drilling fluid to effectively bridge the pores in the filtermedium and, therefore, the ability of the mud to reduce formation damage in the reservoir. The apparatus resembles a high-pressure, high-temperature filtration cell that has been modified to operate upside down (to remove the effects of gravity) and to accept filter media of different permeabilities (sintered metal, which is chosen for higher temperature conditions, aloxite, which is a porous ceramic material, or rock). The medium is selected to match the permeability of the reservoir to be drilled. The filter medium is at the top so that sediment will not affect the filter cake. Pressure is applied hydraulically from below.

The weight, or net volume, of solid particles that fall into each of the various size ranges, given as a percentage of the total solids of all sizes in the sample of interest. Particle size can be determined by sieve analysis, light scattering, passage through an electrically charged orifice, settling rate or other methods. Data are typically shown as a histogram chart with percentage-smaller-than on the y-axis and size ranges on the x-axis. Mud engineers use such data to operate solids-control equipment effectively. Particle-size distributions are used to evaluate bridging materials for drill-in and completion fluids. Barite and hematite samples are examined to ensure performance without excessive wear on equipment and as an API/ISO quality specification.

A specialized apparatus used in the particle-plugging test. The PPA is used to determine the ability of particles in the drilling fluid to effectively bridge the pores in the filter medium and, therefore, the ability of the mud to reduce formation damage in the reservoir. The apparatus resembles a high-pressure, high-temperature filtration cell that has been modified to operate upside down (to remove the effects of gravity) and to accept filter media of different permeabilities (sintered metal, which is chosen for higher temperature conditions, aloxite, which is a porous ceramic material, or rock). The medium is selected to match the permeability of the reservoir to be drilled. The filter medium is at the top so that sediment will not affect the filter cake. Pressure is applied hydraulically from below.

A test performed in a specialized filtration-type apparatus (particle-plugging apparatus) to determine the effectiveness of additives to prevent fluid loss into a permeable medium.

The weight, or net volume, of solid particles that fall into each of the various size ranges, given as a percentage of the total solids of all sizes in the sample of interest. Particle size can be determined by sieve analysis, light scattering, passage through an electrically charged orifice, settling rate or other methods. Data are typically shown as a histogram chart with percentage-smaller-than on the y-axis and size ranges on the x-axis. Mud engineers use such data to operate solids-control equipment effectively. Particle-size distributions are used to evaluate bridging materials for drill-in and completion fluids. Barite and hematite samples are examined to ensure performance without excessive wear on equipment and as an API/ISO quality specification.

The degree of solubilization of a solute into each of multiple immiscible phases at equilibrium. For example, a water-soluble surfactant injected as part of an enhanced oil recovery flood will partially solubilize, or partition, in the oil phase. The degree of partitioning will influence the efficiency of the enhanced oil recovery agent.

A crew that acquires a survey or geophysical data.

The ultimate leader of a survey crew.

The actual leader of a survey crew. The party manager reports to the party chief.

(noun) In production logging, a single traverse of a logging tool through the wellbore, either upward or downward, during which measurements are recorded. Multiple passes at different logging speeds and flow conditions are typically made to ensure data quality and repeatability.

The margin of a continent and ocean that does not coincide with the boundary of a lithospheric plate and along which collision is not occurring. Passive margins are characterized by rifted, rotated fault blocks of thick sediment, such as the present-day Gulf of Mexico and Atlantic margins of North America.

A reservoir or portion of a reservoir that contains economically producible hydrocarbons. The term derives from the fact that it is capable of "paying" an income. Pay is also called pay sand or pay zone. The overall interval in which pay sections occur is the gross pay; the smaller portions of the gross pay that meet local criteria for pay (such as minimum porosity, permeability and hydrocarbon saturation) are net pay.

The point at which all costs of leasing, exploring, drilling and operating have been recovered from production of a well or wells as defined by contractual agreement.

The maximum positive or upward deflection, also known as the crest, of the seismic wavelet. The trough is the maximum negative amplitude or downward deflection of the wave. Seismic interpreters commonly pick or interpret seismic data on paper sections along the trough of a wavelet rather than the normally solid-filled peak for ease of viewing.

A type of short-path multiple, or multiply-reflected seismic energy, having an asymmetric path. Short-path multiples are added to primary reflections, tend to come from shallow subsurface phenomena and highly cyclical deposition, and can be suppressed by seismic processing. In some cases, the period of the peg-leg multiple is so brief that it interferes with primary reflections, and its interference causes a loss of high frequencies in the wavelet.

A standard laboratory instrument used to measure interfacial tension. The method is particularly applicable to relatively high interfacial tensions, but with care can measure down to approximately 1 mN/m. A drop of the denser liquid is poised at the end of a square-ended syringe needle. The drop is of sufficient size that its shape is deformed by gravity, but not so large that it detaches from the syringe. Its shape is determined by the balance of interfacial tension and gravity. The interfacial tension can be obtained from the drop shape and the densities of the two liquids. The method works equally well for a drop of the less-dense liquid by inverting the syringe. This inverted configuration can be useful if the less-dense liquid is opaque.

To disperse a substance into a colloidal form or to disperse a clay in water to form a colloidal suspension.

A clay that has been treated during manufacturing to enhance its dispersion.Reference:Garrett RL: "Quality Requirements for Industrial Minerals Used in Drilling Fluids," Mining Engineering 39, no. 11 (November 1987): 1011-1016.

A product that enhances dispersion of a substance (such as clay) into colloidal form. Peptizing agents for drilling-mud clays are sodium carbonate, sodium metaphosphates, sodium polyacrylates, sodium hydroxide and other water-soluble sodium compounds, even common table salt, NaCl, if added at low concentration. The divalent cations on a clay are replaced by the sodium cations, aiding clay hydration and dispersion. Greater benefit is attained by an agent that contributes an anion (for example, carbonate, phosphate or polyacrylate) that precipitates divalent cations and removes them from solution. This process is successful only when the water first contacted is free of hardness ions, otherwise the anion in the peptizing salt (or polymer) will be precipitated by the hard water and make the peptizing agent much less effective.

The creation of holes in the casing or liner to achieve efficient communication between the reservoir and the wellbore. This process is integral to the optimal creation of hydraulic fractures. Geomechanical analysis is commonly conducted before perforating shale reservoirs to account for the relationship between formation stresses and productivity.

To create holes in the liner or casing under conditions in which the hydrostatic pressure inside the casing or liner is greater than the reservoir pressure. When the perforation is made, there will be a tendency for the wellbore fluid to flow into the reservoir formation.

To create holes in the liner or casing under conditions in which the hydrostatic pressure inside the casing or liner is less than the reservoir pressure. When the perforation is made, there will be a tendency for the reservoir fluid to flow into the wellbore.

The section of wellbore that has been prepared for production by creating channels between the reservoirformation and the wellbore. In many cases, long reservoir sections will be perforated in several intervals, with short sections of unperforated casing between each interval to enable isolation devices, like packers, to be set for subsequent treatments or remedial operations.

A wellbore tubular in which slots or holes have been made before the string is assembled and run into the wellbore. Perforated liners typically are used in small-diameter wellbores or in sidetracks within the reservoir where there is no need for the liner to be cemented in place, as is required for zonal isolation.

An acid treatment placed in the wellbore over the interval to be perforated. Because of the overbalance conditions at the time of perforating, the perforating acid is forced into the newly formed perforation tunnel to stimulate the crushed zone. Formulation of the perforating acid depends on the characteristics of the formation and the downhole equipment used.

(noun) A shaped explosive device, typically consisting of a metal case, explosive liner, and detonating cord, that is loaded into a perforating gun and detonated downhole to create a high-velocity jet capable of penetrating casing, cement, and formation rock to establish flow communication between the reservoir and the wellbore.

A wireline log run to provide a means of depth correlation by comparing the position of casing collars to the reference log (gamma ray log). A short casing joint generally is run near the area to be perforated to assist in the correlation process.

A specially prepared fluid placed in the wellbore over the interval to be perforated. The ideal fluid is clean and solids-free (filtered), and will not react to cause damaging by-products on contact with the reservoir formation. Perforating in a dirty fluid may result in significant permeabilitydamage that is difficult to treat and remove.

A device used to perforate oil and gas wells in preparation for production. Containing several shaped explosive charges, perforating guns are available in a range of sizes and configurations. The diameter of the gun used is typically determined by the presence of wellbore restrictions or limitations imposed by the surface equipment.

The communication tunnel created from the casing or liner into the reservoir formation, through which oil or gas is produced. The most common method uses jet perforating guns equipped with shaped explosive charges. However, other perforating methods include bullet perforating, abrasive jetting or high-pressure fluid jetting.

The number of perforations per linear foot. This term is used to describe the configuration of perforating guns or the placement of perforations, and is often abbreviated to spf (shots per foot). An example would be an 8 spf casing gun.

A measure, or indicator, of the length that a useable perforation tunnel extends beyond the casing or liner into the reservoir formation. In most cases, a high penetration is desirable to enable access to that part of the formation that has not been damaged by the drilling or completion processes.

The radial distribution of successive perforating charges around the gun axis. Perforating gun assemblies are commonly available in 0-, 180-, 120-, 90- and 60-degree phasing. The 0-degree phasing is generally used only in small outside-diameter guns, while 60, 90 and 120 degree phase guns are generally larger but provide more efficient flow characteristics near the wellbore.

A graphical representation of harmonic information in a data set. Often taken from Fourier analysis of the data, this representation is used to determine periodicities in petrophysical data and in geological depositional sequences.

The permanently frozen subsoil that lies below the upper layer (the upper several inches to feet) of soil in arctic regions.

The level to which all subsurface depths in an area are referred, normally the mean sea level. In individual wells, the depth is measured from the depth reference. However, in order to compare data between wells it is important to have a valid, area wide reference for comparison. This is the permanent datum level.

A situation in which the well and the reservoir are continuously monitored. On the basis of this information, the well completion may be adjusted remotely to adapt to changes in downhole conditions. A permanent well monitoring system is composed of the following:· Inflow control valves that enable choking or shutting off different zones according performance such as drawdown, GOR or water cut· Downhole sensors that register pressure, fluid flow rate and temperature· Control lines for power transmission and transferring of monitored downhole data captured by downhole sensors.· A surface control unit to handle the monitored data and for remote operation of the downhole inflow control valves.Wells with permanent monitoring systems are commonly called intelligent or smart wells. Permanent well monitoring is commonly used in multilateral wells, where hydraulically independent valves control the flow of each lateral and in deepwater wells, where well-intervention operations are often prohibitively expensive.Permanent well monitoring helps improve reservoir management by quickly choking or shutting off zones, avoiding expensive well intervention. It also helps maximize production and optimize recovery.

The capability of a rock to allow passage of fluids through it. The term was basically defined by Darcy, who showed that the common mathematics of heat transfer could be modified to adequately describe fluid flow in porous media.

The product of formationpermeability, k, and producing formation thickness, h, in a producing well, referred to as kh. This product is the primary finding of buildup and drawdown tests and is a key factor in the flow potential of a well. It is used for a large number of reservoir engineering calculations such as prediction of future performance, secondary and tertiary recovery potential, and potential success of well-stimulation procedures. Obtaining the best possible value of this product is the primary objective of transient well tests. To separate the elements of the product, it is necessary to have some independent measurement of one of them, usually the estimation of producing formation thickness from well logs. Permeability is then calculated, provided that the fluid formation volume factor and viscosity are known. The accuracy of the calculated permeability is entirely dependent on the accuracy of the estimated formation thickness and the fluid properties.

An apparatus for measuring the permeability of a core sample. Measurements are made either by placing the sample in a chamber (also known as a core holder), or by placing a probe on the surface of the sample. Core-holder measurements are made either with gas or liquid, and either in steady state or unsteady-state conditions. Other variables include the confining pressure and the direction of measurement, which can be axial (along the axis of a cylindrical core sample), transverse (perpendicular to the axis), or radial (to the center of a hollow cylinder). In probe measurements, gas is injected into the sample under either steady- or unsteady-state conditions. Probe permeameters are also known as minipermeameters.

Generally, the distance between a receiver and a source in a survey, such as an electromagnetic survey. In seismic surveys, perpendicular or normal offset is the component of the distance between the source and geophones at a right angle to the spread.

The resistivity of a formation measured by flowing current perpendicular to the bedding planes. In anisotropic formations, the parallel and perpendicular resistivities are different.

(noun) A production logging tool consisting of a flexible, flower-shaped metal basket that expands against the casing or tubing wall to divert all fluid flow through a central spinner or sensor, providing a full-bore flow rate measurement in deviated or horizontal wells where conventional spinner flowmeters may underperform.

The examination of rocks in thin section. Rock samples can be glued to a glass slide and the rock ground to 0.03-mm thickness in order to observe mineralogy and texture using a microscope. (A petrographic microscope is a transmitted-light polarizing microscope.) Samples of sedimentary rock can be impregnated with blue epoxy to highlight porosity.

A complex mixture of naturally occurring hydrocarbon compounds found in rock. Petroleum can range from solid to gas, but the term is generally used to refer to liquid crude oil. Impurities such as sulfur, oxygen and nitrogen are common in petroleum. There is considerable variation in color, gravity, odor, sulfur content and viscosity in petroleum from different areas.

Geologic components and processes necessary to generate and store hydrocarbons, including a mature source rock, migration pathway, reservoir rock, trap and seal. Appropriate relative timing of formation of these elements and the processes of generation, migration and accumulation are necessary for hydrocarbons to accumulate and be preserved. The components and critical timing relationships of a petroleum system can be displayed in a chart that shows geologic time along the horizontal axis and the petroleum system elements along the vertical axis. Exploration plays and prospects are typically developed in basins or regions in which a complete petroleum system has some likelihood of existing.

A technique used to represent the history of a sedimentary basin, including the processes and components necessary to form petroleum: a petroleum sourcerock, a reservoir, a trapping mechanism, a seal, and the appropriate relative timing of formation of these. Using geologic, geophysical, and engineering data, scientists create a 3D model of the subsurface that can be used to understand whether petroleum is present and how much might exist in potential traps. Petroleum systems models can be used to help predict porepressure and plan well construction and fielddevelopment. A useful petroleum systems model can be used to identify and explain inconsistencies in the data. The resulting models are valuable during exploration for identifying resource richness, such as sweet spots in unconventional plays such as shale gas, and during field development and production for improving completion efficiency.Petroleum systems modeling is distinct from reservoir simulation in that it covers a larger scale that might include multiple oil and gas fields and considers a geologic time frame of millions of years rather than a production time frame of years or decades.

The study of macroscopic features of rocks, such as their occurrence, origin and history, and structure (usually by examining outcrops in the field) and their texture and composition (by studying smaller samples more closely).

A model of a reservoir or a field in which the petrophysical data were the only or the primary data used to construct the model.

Rock types that have been classified according to their petrophysical properties, especially properties that pertain to fluid behavior within the rock, such as porosity, capillary pressure, permeabilities, irreducible saturations or saturations. Petrophysical rock types are often calibrated from core and dynamic data, but are usually calculated from wireline logs, where possible, because the wireline logs are generally the only measurements that are available for all wells at all depths. Electrofacies approaches are often used to determine rock types from logs.

An interpretation of the presumed continuation of an event. In areas of discontinuous, divergent reflectors or incoherent data, drawing phantoms allows the interpreter to generate a map on a discontinuous event.

A description of the motion of, or means of comparison of, periodic waves such as seismic waves. Waves that have the same shape, symmetry and frequency and that reach maximum and minimum values simultaneously are in phase. Waves that are not in phase are typically described by the angular difference between them, such as, "180 degrees out of phase." Zero-phase wavelets are symmetrical in shape about zero time whereas non-zero-phase wavelets are asymmetrical. Non-zero-phase wavelets are converted to zero-phase wavelets to achieve the best resolution of the seismic data. Known (zero) phase well synthetics and vertical seismic profiles (VSPs) can be compared with local surface seismic data to determine the relative phase of the surface seismic wavelets. Such knowledge allows the surface seismic data to be "corrected" to zero phase. The units of phase are degrees.

A pressure phenomenon caused in a wellbore by rise of gas and fall of liquids trapped in a wellbore after a surface shut-in. This phenomenon can cause a "hump" in the buildup curve, and frequently leads to incorrect analysis of buildup test results because the entire early portion of the transient is adversely affected by this pressure response.

The change in position of the peaks of a sinusoidal electromagnetic wave as it passes through the formation. If the sinusoidal wave picked up by two receivers a certain distance apart in a formation are compared, it is found that the wave has been attenuated and shifted in time. The shift is known as a phase shift. The term is used in particular with reference to the propagation resistivity log and the electromagnetic propagation log.

The ability of the formation to resist electrical conduction, as derived from the change in position of the peaks of an electromagnetic wave generated in a propagation resistivity measurement. At the frequencies used, the phase shift depends mainly on the resistivity of the material with a small dependence on dielectric permittivity, particularly at high resistivity. Common practice is to transform the phase shift to resistivity assuming that the dielectric permittivity is related to resistivity by a simple algorithm. The transform also depends on transmitter/receiver spacings and tool design. For a 2-MHz measurement, a typical measurement range is 0.2 to 200 ohm-m. Above 200 ohm-m, the dielectric effects become too variable and it is preferable to use the dielectric resistivity.

A record of the velocity with which a particular phase (gas, oil or water) moves in a producing well. While most flowmeters measure some average of all the fluids, the phase-velocity log identifies one particular phase. This is particularly important in highly deviated and horizontal wells with multiphase flow, where the flow structure is complicated.Phase-velocity measurements are made with either the crosscorrelation flowmeter, the water-flow log, or with chemical markers designed to mix specifically with one particular phase. Velocity-shot measurements, using radioactive tracers, have also been used. In a typical chemical marker technique, a gadolinium-rich marker is injected into the flow stream, dissolving in either oil or water. Gadolinium has a high capture cross section, or sigma, so that a slug of fluid with high sigma moves with the appropriate phase up the borehole. This slug can be detected by a standard pulsed-neutron capture tool, and the velocity of the phase computed from the time of flight between ejector and detector.

A pH indicator that is clear below pH 8.3 and red above 8.3. It is the indicator used in various alkalinity titrations.

A group of salts formed by neutralization of phosphorous or phosphoric acid with a base, such as NaOH or KOH. Orthophosphates are phosphoric acid (H3PO4) salts, where 1, 2 or 3 of the hydrogen ions are neutralized. Neutralization with NaOH gives three sodium orthophosphates: (a) monosodium phosphate (MSP), (b) disodium phosphate (DSP) or (c) trisodium phosphate (TSP). Their solutions are buffers in the 4.6 to 12 pH range. TSP is an excellent degreaser. All will precipitate hardness ions such as calcium. Polyphosphates are polymers made from various orthophosphates by dehydration with heat. Sodium acid pyrophosphate (SAPP) is a claydeflocculant and treatment for cement contamination. For clay deflocculation, polyphosphates are limited by the temperature at which they hydrolyze back to orthophosphates, although several that performed up to 280°F [138°C] have been documented in the literature (see reference).Reference:Sikorski CF and Weintritt DJ: "Polyphosphate Drilling-Mud Thinners Deserve Second Look," Oil & Gas Journal 81, no. 27 (July 4, 1983): 71-78.

A gamma ray interaction in which the gamma ray is fully absorbed by a bound electron. If the energy transferred exceeds the binding energy to the atom, the electron will be ejected. Normally, the ejected electron will be replaced within the material and a characteristic X-ray will be emitted with an energy that is dependent on the atomic number of the material. The highest probability for this effect occurs at low gamma ray energy and in a material of high atomic number. The photoelectric effect is the principle behind the PEF log, which identifies lithology.

A record of the density in and around a completed well using a radioactive source of gamma rays and a detector. The log is recorded with a nuclear fluid densimeter. Originally, photon logs were run to determine the size of salt caverns. More recently, they have been run to evaluate the quality of gravel packs and sand cavities, and are then synonymous with gravel-pack logs.

To interpret data, such as seismic sections, by selecting and tracking marker beds or other events.

The depth at which the tool string is picked up off the bottom of the well during a wireline logging survey. Pick-up can be observed by an increase in cable tension and by the start of activity in the log curves. When the logging tool is lowered to the bottom of the well, it is common practice to spool in some extra cable. When the cable is pulled back out, the tool remains stationary before it is picked up off the bottom. During this time the log readings are static but the depth, which is recorded by the movement of the cable, is changing.

To use a relatively weak, inhibited acid to remove scale, rust and similar deposits from the internal surfaces of equipment such as treating lines, pumping equipment or the tubing string through which an acid or chemical treatment is to be pumped. The pickling process removes materials that may react with the main treatment fluid to create undesirable secondary reactions or precipitates damaging to the near-wellbore reservoirformation.

To run a scraper, or pig, through a pipeline for cleaning purposes.

The trip of a pig through a pipeline for cleaning purposes.

The act of forcing a device called a pig through a pipeline for the purposes of displacing or separating fluids, and cleaning or inspecting the line.

A relatively small volume of specially prepared fluid placed or circulated in the wellbore. Fluid pills are commonly prepared for a variety of special functions, such as a sweep pill prepared at high viscosity to circulate around the wellbore and pick up debris or wellbore fill. In counteracting lost-circulation problems, a lost-circulation pill prepared with flaked or fibrous material is designed to plug the perforations or formation interval losing the fluid.

A downhole milling tool designed with an extended pilot or central stinger section that is inserted in the bore of the packer, tubular or equipment being milled. This design helps ensure that the mill follows the desired path and does not damage the casing or liner wall as the milling operation progresses.

An experimental test, or series of tests, used to predict mud behavior and guide future actions by the mud engineer. Rather than experimenting on the full mud volume and risking serious and expensive mistakes, pilot tests such as those listed below give valuable guidance:(1) Weight-up tests evaluate how much mud weight can be increased.(2) Dilution tests evaluate how much prior dilution is needed in order to weight up.(3) Product tests evaluate similar additives for performance to select the best material.(4) Heat-aging tests evaluate how a mud will react if exposed to high temperature while circulating or while static in the hole.(5) Contamination tests evaluate how mud will respond to an expected contaminant.(6) Contaminant-treatment tests evaluate how contaminated mud will respond to various amounts and types of treatments.Pilot test samples are formulated using the concept of barrel equivalent.

Relating to the male threadform, as in the "pin end of the pipe."

(verb) To progressively thin and terminate laterally, as when a geological formation, reservoir sand, or coal seam tapers to zero thickness against an unconformity, fault, or facies change. Pinch-out geometries can form stratigraphic traps capable of containing hydrocarbon accumulations.

A reduction in bed thickness resulting from onlapping stratigraphic sequences.

A specially formulated blend of lubricating grease and fine metallic particles that prevents thread galling (a particular form of metal-to-metal damage) and seals the roots of threads. The American Petroleum Institute (API) specifies properties of pipe dope, including its coefficient of friction. The rig crew applies copious amounts of pipe dope to the drillpipe tool joints every time a connection is made.

Offshore, the storage bins for drillpipe, drill collars and casing. The offshore pipe rack functions similarly to the onshore version. Due to space limitations, offshore pipe racks tend to be narrower and routinely contain many layers of pipe. The onshore pipe rack tends to have few stacked layers and instead extends laterally as needed to hold the tubular goods because space is not at a premium.

A type of sealing element in high-pressure split seal blowout preventers that is manufactured with a half-circle hole on the edge (to mate with another horizontally opposed pipe ram) sized to fit around drillpipe. Most pipe rams fit only one size or a small range of drillpipe sizes and do not close properly around drillpipe tool joints or drill collars. A relatively new style is the variable bore ram, which is designed and manufactured to properly seal on a wider range of pipe sizes.

The increase in length resulting from the combination of forces acting on a string within the wellbore. The principal factors resulting in an increase in string length are the weight of the string itself and the effects of thermal expansion.

A tube or system of tubes used for transporting crude oil and natural gas from the field or gathering system to the refinery.

The quantity (volume) of oil and gas required to maintain a full pipeline. The static capacity of a pipeline is usually expressed as a volume per unit length (for example, bbl/ft). Nevertheless, the fluid volume passing through a pipeline in a specific time period will depend on initial pressure, flow characteristics, ground elevation, density and delivery pressure.

A sufficiently dry gas that will not drop out natural gas liquids (NGL) when entering the gas pipeline; also, gas with enough pressure to enter high-pressure gas pipelines.

Oil whose free water, sediment and emulsion content (BS&W) is sufficiently low to be acceptable for pipeline shipment.

An inspection of a pipeline to check for leaks, washouts or other abnormal conditions. A pipeline patrol is commonly performed using airplanes.

A type of corrosion in which there is loss of metal in localized areas. The corrosion rate in the pits is many times greater than the corrosion rate on the entire surface.The resultant pits can be large and shallow or narrow and deep. Pitting is a more dangerous problem than general corrosion because the pitted areas can be easily penetrated.

A flat drawing board mounted on a tripod used in combination with an alidade to construct topographic or geologic maps in the field. A sheet of paper or mylar covering the plane table is annotated during map construction.

A wave that is far enough from its source that its wavefront has no effective curvature, or is planar, over a short distance. Seismic and electromagnetic waves are treated as plane waves even though that assumption is not strictly correct.

Minute organisms that float or drift passively near the surface of oceans and seas. Plant-like plankton, or phytoplankton, include diatoms. Zooplankton are animals that have a limited ability to move themselves. The changes in plankton over time are useful for estimation of relative ages of rocks that contain the fossilized remains of plankton.

To place seismometers on the ground. The seismometer should be firmly stuck or planted in the ground in the proper location and orientation for optimal seismic acquisition.

Pertaining to a material that can deform permanently without rupturing.

Permanent mechanical or physical alteration that does not include rupture. Plastic deformation of rocks typically occurs at high temperatures and pressures, conditions under which rocks become relatively viscous.

A fluid in which the shear force is not proportional to the shear rate (non-Newtonian) and that requires a finite shear stress to start and maintain flow. Most drilling muds are characterized as either plastic or pseudoplastic fluids.

A parameter of the Bingham plastic model. PV is the slope of the shear stress/shear rate line above the yield point. PV represents the viscosity of a mud when extrapolated to infinite shear rate on the basis of the mathematics of the Bingham model. (Yield point, YP, is the other parameter of that model.) A low PV indicates that the mud is capable of drilling rapidly because of the low viscosity of mud exiting at the bit. High PV is caused by a viscous base fluid and by excess colloidal solids. To lower PV, a reduction in solids content can be achieved by dilution of the mud.

To stay on the surface of the formation or a perforation tunnel. When, for example, bead tracers are injected into a well, they will be carried by the injection fluid. Instead of entering the formation with the fluid, the bead tracers will be held, like plates, on the surface.

The unifying geologic theory developed to explain observations that interactions of the brittle plates of the lithosphere with each other and with the softer underlying asthenosphere result in large-scale changes in the Earth. The theory of plate tectonics initially stemmed from observations of the shapes of the continents, particularly South America and Africa, which fit together like pieces in a jigsaw puzzle and have similar rocks and fossils despite being separated by a modern ocean. As lithospheric plates heat up or cool down depending on their position, or their tectonic environment, relative to each other and to warmer areas deeper within the Earth, they become relatively more or less dense than the asthenosphere and thus tend to rise as molten magma or sink in cold, brittle slabs or slide past each other. Mountain belts can form during plate collisions or an orogeny; diverging plates or rifts can create new midoceanic ridges; plates that slide past one another create transform fault zones (such as the San Andreas fault); and zones of subduction occur where one lithospheric plate moves beneath another. Plate tectonic theory can explain such phenomena as earthquakes, volcanic or other igneous activity, midoceanic ridges and the relative youth of the oceanic crust, and the formation of sedimentary basins on the basis of their relationships to lithospheric plate boundaries. Convection of the mantle is postulated to be the driving mechanism for the movement of lithospheric plates. Measurements of the continents using the Global Positioning System confirm the relative motions of plates. Age determinations of the oceanic crust confirm that such crust is much younger than that of the continents and has been recycled by the process of subduction and regenerated at midoceanic ridges.

A topographic feature consisting of a large flat area at a relatively high elevation with steep sides.

A relatively flat, nearly level area of sedimentary rocks in a continent that overlies or abuts the basement rocks of a craton.

To pursue hydrocarbon accumulations of a given type.

A log that has been generated from digital data some time after the actual acquisition of the data. It is distinct from the acquisition log. Some of the parameters for processing the log may or may not be different from those of the acquisition log.

To prepare a wellbore to be shut in and permanently isolated. There are typically regulatory requirements associated with the P&A process to ensure that strata, particularly freshwater aquifers, are adequately isolated. In most cases, a series of cement plugs is set in the wellbore, with an inflow or integrity test made at each stage to confirm hydraulic isolation.

A multiphase flow regime in pipes in which most of the gas moves as large bubbles dispersed within a continuous liquid. The bubbles may span much of the pipe. There are also small bubbles within the liquid, but many of these have coalesced to form the larger bubbles, or plugs. In near-horizontal wells, the plugs are also known as elongated bubbles. Plug flow is similar to slug flow, but the bubbles are generally smaller and move more slowly.

A solid or gel in a workover or drilling fluid that blocks off permeable zones to prevent loss of fluid into those permeable zones or to protect those zones from damage. The plugging may be temporary or permanent.

The angle between a linear feature and a horizontal line in a vertical plane containing both lines.

A type of gas-lift method that uses a plunger that goes up and down inside the tubing. The plunger provides an interface between the liquid phase and the lift gas, minimizing liquid fallback. The plunger has a bypass valve that opens at the top of the tubing and closes when it reaches the bottom. Plunger-lift methods are used to remove water and condensate from a well, but they can handle only a limited column of liquid. Typically, these methods are applied on gas wells with high gas liquid ratio (GLR) to operate only with formation gas.

(noun) The additional stroke distance beyond the designed plunger travel in a sucker rod pumping system, occurring when the pump plunger descends past its normal bottom position due to rod stretch or fluid pound. Excessive overtravel can cause mechanical damage to the pump barrel and reduce pump efficiency.

An arcuate deposit of sediment, usually sand, that occurs along the convex inner edges of the meanders of channels and builds outward as the stream channel migrates.

A term used to describe the beginning of thickening of a cementslurry during the thickening-time test, often abbreviated as POD. For some slurries, the POD is used as the thickening time.

In chemistry, referring to a compound in which electrons are not shared equally in the chemical bond, resulting in partial electrical charges. The best example is water, H2O, where the oxygen atom "pulls" the electrons more strongly than the hydrogen atoms and has a partial negative charge. The hydrogen atoms thus carry a partial positive charge. Polar compounds may ionize partially when dissolved in water.

A compound whose electrons are not shared equally in chemical bonds. A polar compound is not necessarily ionized. Water is a polar compound. Polymers can have ionizing polar groups on their complex structures.

The nature of the positive and negative portions of the seismic wavelet, the positive and negative aspects of electrical equipment, or the north and south orientations of magnets and the Earth's magnetic field.

The convention adopted by the Society of Exploration Geophysicists (SEG) for the display of zero-phaseseismic data. If the signal arises from a reflection that indicates an increase in acoustic impedance, the polarity is, by convention, positive and is displayed as a peak. If the signal arises from a reflection that indicates a decrease in acoustic impedance, the polarity is negative and is displayed as a trough. There is another standard for minimum-phase data. In order to interpret seismic data acquired at different times within a region, to model data, or to assess bright or dim spots, some knowledge of the polarity of the data is essential to correlate or tie data properly.

The effect on a propagation resistivity or induction log of charge buildup at the boundary between two formation layers with different dielectric properties. In a vertical well with horizontal layers, the current loops generated by the tool in the formation are parallel to the layers and do not cross bed boundaries. However, with an apparent dip between borehole and formation, the loops cross the bed boundaries and generate a charge buildup at the boundaries. The charge buildup acts like a secondary transmitter that increases the measured resistivity. The result is a spike to high resistivity as the tool crosses the bed boundary. In deviated or horizontal wells, polarization horns on measurements-while-drilling propagation logs often are used to detect a bed boundary.The spike increases with apparent dip and resistivity contrast between beds. The magnitude of polarization spikes varies with tool type and spacing, being larger for the propagation tools.

The time allotted for the alignment of hydrogen atoms with the static magnetic field during a nuclear magnetic resonance (NMR) measurement. The alignment of hydrogen atoms follows an exponential rule such that after a polarization time PT the percentage aligned is 100*(1 ? e-PT/T1) where T1 is their longitudinal relaxation time. An infinite polarization time is therefore needed to align every hydrogen atom, but 95% are aligned after a time of 3*T1. Typical polarization times for a standard NMR log are between 1 and 4 s.

A generic term for a completion component that has been polished or prepared to enable an efficient hydraulic seal. The polished joint may have an internal or external polished surface and is typically configured in a length that enables some movement of the completion string or associated components without compromising the hydraulic seal.

The uppermost joint in the string of sucker rods used in a rod pump artificial-lift system. The polished rod enables an efficient hydraulic seal to be made around the reciprocating rod string.

A polymer with a high molecular weight. The basic repeating unit or monomer of polyacrylamide is a combination of carbon, hydrogen, oxygen and nitrogen. Polyacrylamides increase the viscosity of the water slug that precedes the final water injection. Polyacrylamides are frequently used as mobility-control buffers in micellar-polymer flooding operations.

A polymer or copolymer of an alkalene oxide, such as polyethylene glycol (PEG), a polymer of ethylene oxide with general formula HO(CH2CH2O)nH, or polypropylene glycol (PPG), which is a polymer of propylene oxide. PAGs are effective shale inhibitors and have effectively replaced the earlier polyglycerols.

One of the synthetic hydrocarbon liquids manufactured from the monomer ethylene, H2C=CH2. Polyalphaolefins have a complex branched structure with an olefin bond in the alpha position of one of the branches. Hydrogenated polyalphaolefins have olefin-carbons saturated with hydrogen, which lends excellent thermal stability to the molecule. Synthetic-base fluids (similar to oil muds) are made with the various types of synthetic liquids because the cuttings can be discharged in offshore waters, whereas discharge of cuttings coated with refined oils would be disallowed.

A cellulose derivative similar in structure, properties and usage in drilling fluids to carboxymethylcellulose. PAC is considered to be a premium product because it typically has a higher degree of carboxymethyl substitution and contains less residual NaCl than technical grade carboxymethylcellulose, although some PACs contain considerable NaCl.

A fluid-loss control additive used in high-temperature, water-base muds. It shows good salt tolerance and temperature tolerance.

A series of alcohols with glycerol, C3H5(OH)3, (usually referred to as glycerin in the USA) being the simplest member. Polyglycerols have been used as shale inhibitors in water-base drilling fluids.

A large molecule made up of repeating units. Some polymers are naturally occurring, such as xanthan gum, guar gum and starch. Other polymers are modified natural polymers, such as carboxymethylcellulose (CMC) and hydropropyl starch and lignosulfonate. Some are synthetic such as polyacrylates, polyacrylamides and polyalphaolefins. Polymers may be classified by their structure and may be linear, branched or less commonly cyclic. Copolymers contain two or more different monomers that can be arranged randomly or in blocks. In solution, entangled polymer chains can create networks, giving complex viscosity behavior. Polymers that ionize in solution are called polyelectrolytes. Charged groups strongly affect behavior and interactions with colloidal clays, other polymers and solvents. Molecular size (weight) influences how a specific polymer type performs in a given type of mud. A small polymer may be a deflocculant, whereas a large polymer of the same type may be a flocculant. Some are viscosifiers and others are fluid-loss control additives while others are multifunctional.

An enhanced oil recovery technique using water viscosified with soluble polymers. Viscosity is increased until the mobility of the injectant is less than that of the oil phase in place, so the mobility ratio is less than unity. This condition maximizes oil-recovery sweep efficiency, creating a smooth flood front without viscous fingering. Polymer flooding is also applied to heterogeneous reservoirs; the viscous injectant flows along high-permeability layers, decreasing the flow rates within them and enhancing sweep of zones with lower permeabilities. The two polymers that are used most frequently in polymer flooding are partially hydrolyzed polyacrylamide and xanthan.

A volume of polymerslurry placed in a wellbore, which, in time and under the correct temperature conditions, will develop to provide a high-viscosity platform on which a cement plug can be placed. Polymer plugs are typically used when a cement plug must be set accurately within the wellbore, The viscous material prevents the dense cement slurry from fingering through the lighter wellbore fluid during placement, helping to ensure that cement is placed over the desired interval.

A generic name for low molecular weight, water-soluble polymers and oligomers containing a large number of hydroxyl groups. Specific examples include glycols, polyglycols and polyglycerols. Polyols are used in water-base fluids as shale inhibitors and gas hydrate inhibitors.

A carbohydrate composed of many monosaccharides. Polysaccharides increase the viscosity of the water slug that precedes the final water injection. However, they are not frequently used in chemical flooding operations because they generate numerous by-products that can potentially plug filters or well sandfaces, especially when they contact polyvalent cations or bacteria.Polysaccharides are also called biopolymers.

A rod shorter than usual, usually placed below the polished rod and used to make a rod string of a desired length.

The accumulation of smaller tracts of land, the sum total acreage of which are required for a governmental agency to grant a well permit or assign a production quota or allowable to an operator.

A type of check valve often used in the lines or manifolds associated with kill and choke lines or pressure-control equipment.

A discrete void within a rock, which can contain air, water, hydrocarbons or other fluids. In a body of rock, the percentage of pore space is the porosity.

The pressure of fluids within the pores of a reservoir, usually hydrostatic pressure, or the pressure exerted by a column of water from the formation's depth to sea level. When impermeable rocks such as shales form as sediments are compacted, their pore fluids cannot always escape and must then support the total overlying rock column, leading to anomalously high formation pressures.

In an intergranular rock, the small pore space at the point where two grains meet, which connects two larger pore volumes. The number, size and distribution of the pore throats control many of the resistivity, flow and capillary-pressure characteristics of the rock.

The pressure of the subsurface formation fluids, commonly expressed as the density of fluid required in the wellbore to balance that pore pressure. A normal gradient might require 9 lbm/gal [1.08 kg/m3], while an extremely high pressure gradient might be 18 lbm/gal [2.16 kg/m3] or higher.

A laboratory test used to determine if a drilling fluid blocks movement of filtrate through pore spaces of a shale sample. The PPT device monitors the increase in pore pressure in a shale when exposed to a drilling fluid over a period of time. Shale cores from 1 to 3-inches long are fitted into a modified Hassler cell that has sensitive pressure transducers in reservoirs on each end of the cell.Reference:van Oort E, Hale AH, Mody FK and Roy S: "Transport in Shales and the Design of Improved Water-Based Shale Drilling Fluids," in SPE Drilling and Completion 11, no. 3 (September 1996): 137-146.

An instrument for measuring the pore volume, and hence the porosity, of a core sample. The term is also used for some instruments that actually measure grain volume, such as the Boyle?s Law Double-Cell method. Pore volume is then obtained from the difference between bulk volume and grain volume.Pore volume is most commonly measured directly by Boyle's Law Single-Cell method, summation of fluids or liquid saturation. Bulk volume is most commonly measured by buoyancy, mercury displacement or a physical measurement of size (calipering); grain volume by Boyle?s law Double-Cell method or disaggregation of the sample.Except for disaggregation, all techniques determine the effective porosity, in the sense of all but the isolated pores.

The percentage of pore volume or void space, or that volume within rock that can contain fluids. Porosity can be a relic of deposition (primary porosity, such as space between grains that were not compacted together completely) or can develop through alteration of the rock (secondary porosity, such as when feldspar grains or fossils are preferentially dissolved from sandstones).Porosity can be generated by the development of fractures, in which case it is called fracture porosity. Effective porosity is the interconnected pore volume in a rock that contributes to fluid flow in a reservoir. It excludes isolated pores. Total porosity is the total void space in the rock whether or not it contributes to fluid flow. Thus, effective porosity is typically less than total porosity.Shale gas reservoirs tend to have relatively high porosity, but the alignment of platy grains such as clays makes their permeability very low.

The exponent, m, in the relation of formation factor (F) to porosity (phi). For a single sample, F is related to phi using the Archie equation F = 1 / phim, with m being the only coefficient needed. In this case, m has been related to many physical parameters, but above all to the tortuosity of the pore space. In theory, it can range from 1 for a bundle of tubes to infinity for porosity that is completely unconnected. For a simple packing of equal spheres, m = 1.5. With a more tortuous pore space or more isolated pores, m increases, while with fractures or conductive solids, m decreases. As a general average for typical reservoir rocks, m is often taken as 2.For a group of rock samples, it is common practice to find a relationship between F and phi that uses two coefficients (F = a / phim). In this case m, like a, becomes an empirical constant of best fit between F and phi, and may take a wide range of values. In complex formations, such as shaly sands or carbonates with multiple pore types, a constant m does not give good results. One solution is to vary m, with the variability related to parameters such as porosity, shaliness, or rock texture, or else determined directly from logs in zones where the water saturation is known or can be computed from a nonresistivity measurement such as electromagnetic propagation.In shaly sands, the preferred solution is to use a saturation equation, such as Waxman-Smits, dual water, SGS or CRMM, in which m is defined as the intrinsic m, determined from the intrinsic formation factor at high salinities or after correction for the effect of shale. In carbonates with multiple pore types, such as fractures, vugs, interparticle porosity and microporosity, one solution is to use equations with different porosity exponents for each pore type. The volume of each pore type must then be determined from logs or borehole images.

A unit equal to the percentage of pore space in a unit volume of rock. It is abbreviated to p.u. and lies between 0 and 100.

A rock or soil with interconnected pores that permit flow of fluids through the medium.

A method for desaturating a core sample by placing one end in capillary contact with a porous plate and applying gas or oil under pressure to the remaining surfaces. The liquid in the original fully saturated sample is expelled through the porous plate. At different pressure stages, the sample is weighed to determine the loss of liquid, and the gas or oil pressure increased. Desaturation continues until no more weight loss is observed, at which time the sample is at irreducible watersaturation. Core samples are desaturated to measure, for example, capillary pressure, irreducible water saturation, resistivity index or nuclear magnetic resonance response.

The product obtained by pulverizing clinker consisting essentially of hydraulic calcium silicates. Portland cement is the most common type of cement used for oil- and gas-well cementing.

Hard granular nodules composed essentially of hydraulic calcium silicates, with smaller quantities of calcium aluminates and ferrites. Portland cement clinker is produced by the heat treatment of cement raw materials in a kiln. Clinker is pulverized with gypsum in the manufacture of portland cement.

A type of fluid pump in which the displacement volume of the pump is fixed for each rotation of the pump. Generally associated with high-pressure applications, positive-displacement pumps are commonly used in drilling operations to circulate the drilling fluid and in a range of oil and gas well treatments, such as cementing, matrix treatments and hydraulic fracturing.

To annotate a map or other display with data at the appropriate location. For example, geologists post formation tops on well logs, isopach maps and seismic profiles. Geophysicists post velocity values and traveltimes on maps before contouring. Engineers contour maps posted with pressure or production data. Posting can become an iterative process as new data become available and interpretations are updated.

Pertaining to a hydrocarbon source rock that has generated as much hydrocarbon as possible and is becoming thermally altered.

An element with an atomic number of 19. The 40K isotope is radioactive, decaying with the emission of a single gamma ray of 1.46 MeV with a half-life of 1.3 * 109 years to give a stable isotope of argon. Potassium is the largest source of natural radioactivity. It occurs in illite, alkali feldspars, micas and some evaporite minerals. It also occurs in some drilling mud systems. The 40K isotope is only a small fraction, about 0.012%, of the total potassium, the main isotope being 39K, which has an abundance of about 1.7% in the Earth's crust. For the purposes of logging, the total potassium is calculated from the measured quantity of 40K and scaled in percent by weight. It is a valuable aid in determining the mineral content of a formation.

The ion of potassium, K+. There are tests used to monitor high (>5000 mg/L) or low (

A class of muds that contain potassium ion (K+) dissolved in the water phase. Potassium muds are the most widely accepted water mud system for drilling water-sensitive shales, especially hard, brittle shales. K+ ions attach to clay surfaces and lend stability to shale exposed to drilling fluids by the bit. The ions also help hold the cuttings together, minimizing dispersion into finer particles. The presence of Na+ ions counteracts the benefits of K+ ions and should be minimized by using fresh water (not sea water) for make-up water. With time, Na+, Ca+2 and other ions accumulate from ion exchange with clays, making the mud less effective, but regular treatment to remove Ca+2 improves polymer function. Potassium chloride, KCl, is the most widely used potassium source. Others are potassium acetate, potassium carbonate, potassium lignite, potassium hydroxide and potassium salt of PHPA. Use of bentonite clay is restricted because of its strong affinity for K+. Instead, various polymers are used. XC polymer and PHPA are used for rheology. For fluid-loss control, mixtures of starch and polyanionic cellulose are often used. CM starch, HP starch, carboxymethylcellulose and sodium polyacrylate (SPA) are also used. PHPA is widely used for shale encapsulation. Potassium, lime and starch-like polymers have also been used as potassium mud systems. Although three API methods exist for determining the K+ ion concentration, the centrifuge method (for K+ >5000 mg/L) is the most accepted field method, and essential for daily monitoring of potassium in a mud. Regular additions of potassium salt maintain shale stability. K+ ion is rapidly consumed while drilling shallow, soft and highly dispersive (gumbo) shales, but maintaining sufficient K+ ion to stabilize gumbo can become expensive when drilling large holes. Researchers, notably Dr. Dennis O'Brien and Dr. Martin Chenevert (while at Exxon Production Research), evaluated different shales, their clay mineralogy and the concentration of K+ needed to stabilize them. Potassium muds above about 1 wt.% K+ ion usually fail the mysid shrimp (US EPA) bioassay test. Therefore, K-muds currently find low acceptance in offshore drilling in USA waters.Reference:O'Brien DE and Chenevert ME: "Stabilizing Sensitive Shales with Inhibited Potassium-Based Drilling Fluids," Journal of Petroleum Technology 25, no. 9 (September 1973): 1089-1100.

A field that satisfies the Laplace equation. The Laplace equation is equivalent in three dimensions to the inverse square law of gravitational or electrical attraction (in source-free regions; in regions with sources, it becomes Poisson's equation). Examples of potential fields include the field of the gravity potential and static electric and magnetic fields.

The temperature at which a fluid ceases to pour. The pour point for oil can be determined under protocols set forth in the ASTM D-97 pour point test, in which the pour point is established as that temperature at which oil ceases to flow when the sample is held at 90 degrees to the upright for five seconds. High pour points usually occur in crude oils that have significant paraffin content. Paraffins (or waxes) will start to precipitate as temperature decreases. At some point the precipitates accumulate to the point where the fluid can no longer flow. This phenomenon can occur with light oils as well as heavy oils.

In hydraulic pumping, the crude oil that is pressurized at surface to energize the bottom pump.

Volume of fluid injected in a well during hydraulic pumping.

A fluid described by the two-parameter rheological model of a pseudoplastic fluid, or a fluid whose viscosity decreases as shear rate increases. Water-base polymer muds, especially those made with XC polymer, fit the power-law mathematical equation better than the Bingham plastic or any other two-parameter model. Power-law fluids can be described mathematically as follows:

A siliceous or siliceous and aluminous material that possesses little or no cementitious value. In a finely divided form and in the presence of moisture, however, pozzolan reacts chemically with calcium hydroxide to form compounds possessing cementitious properties.

Pertaining to material that possesses little or no cementitious value, but that is capable of reacting chemically with calcium hydroxide at ordinary temperatures to form compounds with cementitious properties.

Abbreviation for concentration, parts-per-billion. For example, lead in a water sample is 10 ppb.

Abbreviation for density, pounds-per-gallon, more correctly written lbm/gal. For example, the density of water is 8.33 ppg at 60°F [16°C].

Abbreviation for the expression of concentration, parts-per-million. For solid and liquid concentrations, ppm is stated in weight (mass) units. For example: (1) Calcite in a ground barite sample is 400 ppm. (2) Calcium chloride in a water solution is 250,000 ppm. Note that the relationship of ppm to weight percentage is 10,000 ppm = 1 wt.%. For gases, ppm is in volume (or mole) units. For example, H2S in an air sample is 10 ppm (both by volume or by moles).

A reaction by-product. In sandstoneacidizing, the reaction between hydrofluoric acids [HF] or spent HF acids with formation minerals can precipitate nondamaging products, such as silica, borosilicates or fluoborates. However, other insoluble or difficult to remove by-products can create formation damage.Ferric iron (Fe+3) and ferrous iron (Fe+2) are potential sources for precipitates. Ferric iron present in some formation minerals, including chlorite and glauconite clays, and in tubing rust (iron oxide) can precipitate as ferric hydroxide [Fe(OH)3], which is a gelatinous, highly insoluble mass that can plug pore channels and reduce permeability. The precipitation of ferric hydroxide or ferrous hydroxide [Fe(OH)2] depends on the pH of the spent acid. The former needs a pH higher than 2.2, while the latter requires a pH higher than 7.7. Since the maximum pH for a spent acid is approximately 5.3, the precipitation of ferric hydroxide is more common. Iron-sequestering or iron-reducing agents can be used in acid to maintain the ferric iron in solution.Calcium fluoride [CaF2] precipitates when HF contacts calcite or any other calcium source, and alkali-fluosilicates or iron sulfide form crystal-like by-products that can bridge pore throats. Additionally, some sequestering agents, corrosion inhibitors or friction reducers can also form residues that may plug formation pores.The formation of precipitates can be avoided or reduced by using a preflush, which dissolves calcareous material, iron rust or iron scales, and displaces formation brines (K, Na, Ca ions) away from the wellbore, thereby reducing the formation of CaF2, ferric hydroxide and alkali-fluosilicates.

The formation of an insoluble material in a fluid. Precipitation can occur by a chemical reaction of two or more ions in solution or by changing the temperature of a saturated solution. There are many examples of this important phenomenon in drilling fluids. Precipitation occurs in the reaction between calcium cations and carbonate anions to form insoluble calcium carbonate: Ca+2 + CO3-2 --> CaCO3. When a saturated clear brine first crystallizes, the solid is a precipitate, and is often caused by changing temperature.

The closeness of agreement between the results obtained by applying a measurement procedure several times on identical materials and under prescribed measurement conditions. The smaller the random part of experimental error, the more precise the measurement procedure. (ISO)In logging, the term usually describes the repeatability of a statistical measurement, such as a nuclear log. The precision must then refer to a particular set of conditions, for example, the speed of logging and the formation properties.

The right that a party has reserved or acquired to operate a lease, well, unit and/or concession.

The right that nonselling participating parties have in a lease, well or unit to proportionately acquire the interest that a participating party proposes to sell to a third party.

In chemical flooding, a fluid stage, normally low-salinity water, pumped ahead of the micellar or alkaline chemical solution.One of the purposes of the preflush is to displace reservoirbrine containing potassium, sodium, calcium and magnesium ions from the near-wellbore area, avoiding adverse interactions with the chemical solution. The other purposes are to adjust reservoir salinity to favorable conditions for the surfactant (chemical solution) and to obtain information about reservoir flow patterns. Sometimes a preflush stage is not necessary, especially when brine-tolerant chemical systems are used.

A water-soluble starch that has undergone irreversible changes by heating in water or steam.

To mix with water and allow to react or yield in the water before use. Prehydrating is a common technique for incorporating bentonite in cementslurry or drilling mud. Prehydration may also be done for convenience in cementing operations to allow mixing of water containing the additives with powdered neat cement. Additives also may be prehydrated with mix water to avoid dry-blending the additives with cement.

A concentrated slurry of bentoniteclay mixed in fresh water. The maximum practical concentration of bentonite is about 30 to 40 lbm/bbl because greater concentrations of bentonite are difficult to mix and pump. Water is put into the rig's prehydration tank and the pH raised to 10 or 11 with caustic soda. Soda ash is added as required to remove hardness. Bentonite is slowly added through the mud hopper. Continual energetic mixing and stirring helps the clay particles fully disperse. In some muds, lignosulfonate should be added shortly before mixing the slurry into the active system to protect the colloidal clay particles from flocculation.

The addition of a mud product to fresh water prior to adding it into the mud system. Bentonite clay and XC polymers are two additives whose performance improves by hydration in fresh water before adding them to a highly-treated or salty mud system.

A class of high-performance thread types that are commonly used in modern oilwell and gaswell completions. Premium threads are available in a number of configurations and are typically designed to provide superior hydraulic sealing, improved tensile capacity and ease of make-up. Unlike conventional threads, the sealing areas in premium thread connections are independent of the thread profile and are included as two or three areas within the tool joint, thereby providing some redundancy.

The phase of a petroleum system after hydrocarbons accumulate in a trap and are subject to degradation, remigration, tectonism or other unfavorable or destructive processes.

A core that has been preserved in the same state as when it was brought to the surface. The term implies that the core has been stored for a period before analysis. If this has not been the case, it is known as fresh core. The goal of preservation is to maintain the original fluid content, fluid distribution, rockwettability and mechanical integrity. Preserved cores are typically sealed and protected from mechanical damage. Depending on the core and the objective, they may also be frozen or placed in humidity ovens.Preservation may be wet, in which the core is submerged in a suitably prepared brine, or dry, without any fluid.

The force distributed over a surface, usually measured in pounds force per square inch, or lbf/ in.2, or psi, in US oilfield units.

A rise in well pressure as a function of time observed after a well is shut in or after the production rate is reduced. Buildup pressures are normally measured at or near the bottom of the hole.

An analysis of data obtained from measurements of the bottomhole pressure in a well that is shut-in after a flow period. The profile created on a plot of pressure against time is used with mathematical reservoir models to assess the extent and characteristics of the reservoir and the near-wellbore area.

The maximum pressure an electrical submersible pump can withstand. This pressure is directly related to the differential pressure between the discharge and the suction pressures, and it is always limited by the maximum capacity of the equipment.

The drop in average reservoir pressure from fluid production. All bounded reservoirs have pressure depletion (a drop in average reservoir pressure) associated with fluid production. Water influx counters this effect in reservoirs that are surrounded or underlain by aquifers. Likewise, the presence of a gas cap can slow pressure depletion.

A decline in well pressure with time due to production.

The pressure decline after halting or reducing fluid injection in a well. Pressure falloff tests in injection wells are analogous to pressure buildup tests in production wells.

A device used to measure pressure. Many different types of pressure gauges have been developed for use in well testing over the years. For bottomhole pressure measurements, these include helical bourdon tube gauges, strain gauges, quartz crystal gauges and surface readout gauges. All have their roles, and are still in use. Digital memory gauges are popular at the moment, since the data can be printed out or input directly into a computer for immediate use. Proper use of the data often requires specific knowledge of the possible idiosyncrasies of the particular gauge used in a test.

A change in pressure as a function of distance. This can refer to radial change in pore pressure with distance from the well (which can be calculated from well-test analysis results), to change in pore pressure with depth (which can be measured by formation tests, and implies formation fluid density and/or fluid contacts) or to change in wellbore fluid pressure with depth (which can be measured with production logs, and implies wellbore fluid density).

The evaluation of various well parameters in an attempt to identify when the pore pressure in a drilling well is changing. A team consisting of geologists, engineers and most of the rigsite personnel usually conducts the hunt. The purpose of a pressure hunt is to detect the pore pressure transition (usually from lower to higher pressure) and safely set casing in the transition zone to maximize wellbore strength. A casing string set too shallow, while eliminating some problems associated with drilling fluid contacting the wellbore wall, may not add strength or aid in drilling deeper, perhaps abnormally pressured formations. On the other hand, if drilling is continued too deep into a transition zone, a kick may be taken that cannot be contained in the open wellbore, causing an underground blowout. The hunt team, therefore, seeks to get into the transition zone far enough to gain wellbore strength without taking a kick.

The sensor component in a system used to measure and display the pressure within a vessel or system. The pressure sender may be hydraulically or electrically connected to a remote gauge or display.

A tank designed for storing volatile liquids such as gasoline and liquefied petroleum gases (LPG), which generate high internal pressures. A pressure storage tank is commonly spherical. Other types include spheroidal or hemispherical vessels. Some pressure storage tanks can support several hundred pounds per square inch of internal pressure. A pressure storage tank is also called a pressure-type tank.

A means of assessing reservoir performance by measuring flow rates and pressures under a range of flowing conditions and applying the data to a mathematical model. Fundamental data relating to the interval under test, such as reservoir height and details of the reservoir fluids, are also input. The resulting outputs typically include an assessment of reservoir permeability, the flow capacity of the reservoir and any damage that may be restricting productivity.

A means of assessing reservoir performance by measuring flow rates and pressures under a range of flowing conditions and then applying the data to a mathematical model. In most well tests, a limited amount of fluid is allowed to flow from the formation being tested. The formation is isolated behind cemented casing and perforated at the formation depth or, in openhole, the formation is straddled by a pair of packers that isolate the formation. During the flow period, the pressure at the formation is monitored over time. Then, the formation is closed (or shut in) and the pressure monitored at the formation while the fluid within the formation equilibrates. The analysis of these pressure changes can provide information on the size and shape of the formation as well as its ability to produce fluids.

A graphical representation indicating phase behavior for variation of saturationpressure and injection gas concentration at a given temperature. The diagram indicates conditions for single-phase and two-phase behavior and, within the two-phase region, lines of constant volume fraction, termed quality lines. The diagram is constructed using swelling test saturation pressures and liquid volumes.

The analysis of pressure-transient behavior observed while the well is flowing. Results are generally much less accurate than those from pressure buildup tests because the bottomhole pressure fluctuates rapidly with even slight changes in the surface flow rate. Therefore, pressure buildup tests are much preferred, and analysis of drawdown test data is usually relegated to backup status unless the buildup data are flawed.

A plot of p2 versus time function used to analyze low-pressure gas-well drawdown and buildup tests. The square term arises from substituting a gas-law equation into the differential equations where required to account for fluid compressibility. This allows an approximation for the differential equations that approaches the linear form required to use the classical solutions of the diffusion equation.

The analysis of pressure changes over time, especially those associated with small variations in the volume of fluid. In most well tests, a limited amount of fluid is allowed to flow from the formation being tested and the pressure at the formation monitored over time. Then, the well is closed and the pressure monitored while the fluid within the formation equilibrates. The analysis of these pressure changes can provide information on the size and shape of the formation as well as its ability to produce fluids.

Well tests in which pressure is recorded as a function of time and interpreted using various analysis methods. These include buildup tests and drawdown tests in production wells and falloff tests in injection wells. Pressure-transient well-test analysis procedures are based on classical mathematical relationships between flow rate, pressure and time, which are directly analogous to the theory of heat transfer.

A device to measure density (weight) of a mud, cement or other liquid or slurry under sufficient pressure that the effect of gas bubbles in the liquid is eliminated. The balance consists of a fixed-volume mud cup on one end of a graduated beam and a counterweight on the other end. The beam has a knife-edge as a balance point and a bubble to show when it is level. The mud cup has a screw-on, sealed cap with a valve in the cap to allow connection of a small piston-type hand pump. Operation of the pressurized balance is identical to an ordinary mud balance after pressurization.

The first cementing operation performed to place a cement sheath around a casing or liner. The main objectives of primary cementing include zonal isolation to prevent fluid migration in the annulus, support for the casing or liner, and protection of the casing from corrosive fluids.

The main elements of an oil or gas well, including the production tubing string, that enable a particular type or design of completion to function as designed. The primary completion components depend largely on the completion type, such as the pump and motor assemblies in an electrical submersible pump completion.

The expulsion of newly generated hydrocarbons from a source rock. The further movement of the hydrocarbons into reservoir rock in a hydrocarbon trap or other area of accumulation is secondary migration.

The porosity preserved from deposition through lithification.

(noun) The first stage of hydrocarbon recovery in which oil and gas are produced using the natural energy of the reservoir, including solution gas drive, gas cap expansion, water drive, gravity drainage, and rock and fluid expansion. Primary recovery typically recovers 5% to 30% of the original oil in place, depending on the drive mechanism.

The first stage of hydrocarbonproduction, in which natural reservoir energy, such as gasdrive, waterdrive or gravity drainage, displaces hydrocarbons from the reservoir, into the wellbore and up to surface.Initially, the reservoir pressure is considerably higher than the bottomhole pressure inside the wellbore. This high natural differential pressure drives hydrocarbons toward the well and up to surface. However, as the reservoir pressure declines because of production, so does the differential pressure. To reduce the bottomhole pressure or increase the differential pressure to increase hydrocarbon production, it is necessary to implement an artificial lift system, such as a rod pump, an electrical submersible pump or a gas-lift installation. Production using artificial lift is considered primary recovery.The primary recovery stage reaches its limit either when the reservoir pressure is so low that the production rates are not economical, or when the proportions of gas or water in the production stream are too high. During primary recovery, only a small percentage of the initial hydrocarbons in place are produced, typically around 10% for oil reservoirs.Primary recovery is also called primary production.

The means by which the initial reservoirproduction is achieved, such as natural production from a gas-drive reservoir. In many cases, a secondary recovery method, such as waterflood, is required to maintain a viable reservoir production rate.

Seismic events whose energy has been reflected once. Multiples, in contrast, are events whose energy has been reflected more than once. A goal of seismic data processing is to enhance primary reflections, which are then interpreted as subsurface interfaces.

The period of time during which an oil and gas lease will be in effect, in the absence of production, drilling or other operations specified by the lease. The oil and gas lease can be perpetuated past the primary term by production in paying quantities, drilling, operations and/or the payment of shut-in royalties specified by the lease.

The source of power for the rig location. On modern rigs, the prime mover consists of one to four or more diesel engines. These engines commonly produce several thousand horsepower. Typically, the diesel engines are connected to electric generators. The electrical power is then distributed by a silicon-controlled-rectifier (SCR) system around the rigsite. Rigs that convert diesel power to electricity are known as diesel electric rigs. Older designs transmit power from the diesel engines to certain rig components (drawworks, pumps and rotary table) through a system of mechanical belts, chains and clutches. On these rigs, a smaller electric generator powers lighting and small electrical requirements. These older rigs are referred to as mechanical rigs or more commonly, simply power rigs.

(noun) A flexible, rope-like explosive charge consisting of a core of PETN or RDX explosive within a textile or plastic outer sheath, used to transmit a detonation signal between perforating charges, boosters, or other explosive components in a perforating gun assembly.

The axis along which the data in n-dimensional space is primarily distributed. In two dimensions, the first principal axis is the semimajor axis of the ellipse that best fits the data set. Multiple principal axes are always orthogonal. Data are sometimes rearranged to be in principal component space before further analysis (such as cluster analysis) is performed. Analysis on data that have been transformed into principal component space is referred to as principal component analysis, or PCA.

Analysis of data that has been transformed from the original axes to principal axes, often abbreviated PCA. The first principal axis is the direction in which the data are primarily distributed or the "long" axis of the distribution in n-dimensional space. Data are sometimes rearranged to be in principal component space before further analysis (such as cluster analysis) is performed.

A numerical estimate of the chances of an event occurring given a limited number of opportunities for the event to occur.

In electromagnetic methods, to measure the variation of a property versus depth, including electrical, electromagnetic and magnetotelluric properties. Probing differs from profiling in that the goal of probing is to provide a record of vertical changes, whereas profiling documents lateral variations.

Alteration of seismic data to suppress noise, enhance signal and migrate seismic events to the appropriate location in space. Processing steps typically include analysis of velocities and frequencies, static corrections, deconvolution, normal moveout, dip moveout, stacking, and migration, which can be performed before or after stacking. Seismic processing facilitates better interpretation because subsurface structures and reflection geometries are more apparent.

A generic term used in a number of contexts but most commonly to describe any fluid produced from a wellbore that is not a treatment fluid. The characteristics and phase composition of a produced fluid vary and use of the term often implies an inexact or unknown composition.

A term used to describe water produced from a wellbore that is not a treatment fluid. The characteristics of produced water vary and use of the term often implies an inexact or unknown composition. It is generally accepted that water within the pores of shale reservoirs is not produced due to its low relative permeability and its mobility being lower than that of gas.

An underground rockformation from which oil, gas or water is produced. Any porous rock will contain fluids of some sort, and all rocks at considerable distance below the Earth's surface will initially be under pressure, often related to the hydrostatic column of ground waters above the reservoir. To produce, rocks must also have permeability, or the capacity to permit fluids to flow through them.

A well producing fluids (gas, oil or water).

A measure of the efficiency of seismic acquisition. Production can be expressed in terms of the number of lines, shots or lengths (km or miles) of data acquired in a given time.

Payment by a well operator to a host country upon achievement of certain levels of production.

A casing string that is set across the reservoir interval and within which the primary completion components are installed.

A record of one or more in-situ measurements that describe the nature and behavior of fluids in or around the borehole during production or injection. Production logs are run for the purpose of analyzing dynamic well performance and the productivity or injectivity of different zones, diagnosing problem wells, or monitoring the results of a stimulation or completion. The term is sometimes extended to include logs run to measure the physical condition of the well, for example cement bond and corrosion logs.The earliest production logs consisted of temperature logs (1930s) and flowmeters (1940s), to which were soon added fluid-density and capacitance logs (1950s). Flow-rate measurements were gradually improved by the development of tracer logs and improvement to the basic spinner flowmeter.These techniques were adequate for near-vertical wells with single or biphasic flow, but could be misleading in highly deviated, and especially horizontal, wells. New techniques were developed starting in the 1980s. These techniques focused on local probes to measure holdup at different points in the borehole, nuclear techniques to analyze the total holdup of all three phases, and phase-velocity logs for the analysis of individual fluids. At the same time, complex flow structures and flow regimes have been studied more extensively using flow loops.

A device used to isolate the annulus and anchor or secure the bottom of the production tubing string. A range of production packer designs is available to suit the wellbore geometry and production characteristics of the reservoir fluids.

A portion of proceeds from production, specified by contract, and payable to the lessor or farmor, or host country until total payment has reached a predetermined limit specified by contract.

A fine paid to the host country for failure to attain specified production rates over a defined period of time.

The flow period before a buildup. The duration of the production period should be specified in the test design to assure that a stable flow situation is reached, and that the pressure disturbance has reached far enough into the formation to allow determination of a representative value for kh. For reservoir-limits testing, the production period must be long enough for the pressure disturbance to have reached the boundaries of interest.

An agreement between the parties to a well or wells and a host country to utilize specified goods and services from that country.

An agreement between the parties to a well and a host country regarding the percentage of production each party will receive after the participating parties have recovered a specified amount of costs and expenses.

The primary conduit through which reservoir fluids are produced to surface. The production string is typically assembled with tubing and completion components in a configuration that suits the wellbore conditions and the production method. An important function of the production string is to protect the primary wellbore tubulars, including the casing and liner, from corrosion or erosion by the reservoir fluid.

A wellbore tubular used to produce reservoir fluids. Production tubing is assembled with other completion components to make up the production string. The production tubing selected for any completion should be compatible with the wellbore geometry, reservoir production characteristics and the reservoir fluids.

The portion of a Christmas tree or surface production facility through which production fluids flow. The production wing typically includes a wing valve and a choke to control or isolate flow from the wellbore.

A mathematical means of expressing the ability of a reservoir to deliver fluids to the wellbore. The PI is usually stated as the volume delivered per psi of drawdown at the sandface (bbl/d/psi).

(noun) A well test conducted to measure the flow capacity of a producing well by recording the stabilised flow rate at one or more controlled drawdown pressures. Results are used to calculate the productivity index (PI), determine flow efficiency, and evaluate formation damage or stimulation effectiveness.

To measure the lateral variation of a property, such as gravity or magnetic fields. Probing, in contrast, is the term used to describe the measurement of vertical variations of a property in electromagnetic and other nonseismic geophysical methods.

The process of controlling undesirable water production from a well by conducting treatments to prevent coning or cresting. A range of treatment options is available for profile modification applications, most of which are designed to reduce the permeability of the water-bearing zones to encourage preferential flow from the oil-bearing formation. The injection of polymers, or similar chemicals, that form a rigid gel within the formation matrix is a common treatment.

A procedure that involves sampling gas and liquid at different points across the diameter of pipe to evaluate the degree of stratification at a specific location.

The amount of production, after deducting cost oil production allocated to costs and expenses, that will be divided between the participating parties and the host government under the production sharing contract.

The accumulation of sequences by deposition in which beds are deposited successively basinward because sediment supply exceeds accommodation. Thus, the position of the shoreline migrates into the basin during episodes of progradation, a process called regression.

A type of a sucker rod-pumping unit that uses a rotor and a stator. The rotation of the rods by means of an electric motor at surface causes the fluid contained in a cavity to flow upward. It is also called a rotary positive-displacement unit.

The situation in which 10-second and 10-minute gel strengths for a drilling mud have dissimilar values, with the 10-minute number being much higher than the 10-second number. This indicates that the gelation of the mud is rapidly gaining strength with time, which generally is an undesirable feature of a mud. The mud may require excessive pump pressures to break circulation. If gels appear to be too progressive, a 30-minute gel-strength measurement may be warranted as a third check of progress.

A property of a sinusoidal plane wave equal to twice pi divided by the wavelength. Also known as the wavenumber, the propagation constant is fundamental to the mathematical representation of wavefields. It is the spatial equivalent of angular frequency and expresses the increase in the cycle of the wave (measured in radians) per unit of distance. In nondispersive media, the wavespeed is the ratio of the angular frequency to the propagation constant. The propagation vector has magnitude equal to the propagation constant and points in the direction the wave is traveling.

A measurements-while-drilling log of formation resistivity. The log normally contains at least one attenuation and one phase-shift resistivity reading. In many cases there will be multiple curves of both, the difference being the depth of investigation. For the same nominal depth of investigation, the attenuation resistivity reads deeper than the phase-shift resistivity and is less affected by invasion, but more affected by surrounding beds and apparent dip. The attenuation measurement has a poorer vertical resolution and is less affected by anisotropy. Depths of investigation and vertical resolution of both measurements vary with the average formation resistivity.Although depths of investigation are less than with wireline resistivity logs, the invasion at the time of measurement is usually small and it is possible to derive the resistivity of the undisturbed zone.

A measurement of the formation resistivity made on drillpipe at a frequency in the range of 100 kHz to 10 GHz, most commonly 2 MHz. The basic measurement is accomplished using a transmitter and two receivers. At these frequencies, the response is best explained as the propagation of a wave. Thus, the phase shift and attenuation of the wave between the receivers are measured and transformed to give the phase shift and the attenuation resistivity. In practice, multiple transmitters may be used to obtain different depths of investigation and achieve borehole compensation. The wavelength is such that the borehole has a minor effect, but one for which correction may be needed.

Sized particles mixed with fracturing fluid to hold fractures open after a hydraulic fracturing treatment. In addition to naturally occurring sand grains, man-made or specially engineered proppants, such as resin-coated sand or high-strength ceramic materials like sintered bauxite, may also be used. Proppant materials are carefully sorted for size and sphericity to provide an efficient conduit for production of fluid from the reservoir to the wellbore.

A solvent used with water to break the emulsion of an oil-base or synthetic-base drilling fluid to prepare the sample for chemical titrations to determine lime, calcium or chloride content according to API testing procedures. PNP is an abbreviation for propylene glycol normal propyl ether. It is an environmentally friendlier replacement of a xylene-isopropynol mixture previously used in certain titrations.

A well in which the maximum production rate is fixed by law. These laws were developed by producing states primarily to control the market and avoid periodic price collapses.

The amount of acreage, determined by governmental authority that can be efficiently and economically drained by a well at a particular depth or horizon.

An area of exploration in which hydrocarbons have been predicted to exist in economic quantity. A prospect is commonly an anomaly, such as a geologic structure or a seismic amplitude anomaly, that is recommended by explorationists for drilling a well. Justification for drilling a prospect is made by assembling evidence for an active petroleum system, or reasonable probability of encountering reservoir-quality rock, a trap of sufficient size, adequate sealing rock, and appropriate conditions for generation and migration of hydrocarbons to fill the trap. A single drilling location is also called a prospect, but the term is more properly used in the context of exploration. A group of prospects of a similar nature constitutes a play.

An electrode device with small spacings from which the current flow, and hence the measurement, is focused a short distance into the formation. The proximity log measures the resistivity of the flushed zone with minimum influence from the mudcake or the undisturbed zone. The central current-emitting electrode (A0) is surrounded by a guard electrode that emits sufficient current to focus the current from A0 a certain distance into the formation. The electrodes are mounted on a pad that is pressed against the borehole wall. In a typical tool design, 90% of the signal comes from within 5 to 10 in. [13 to 25 cm] of the pad. This is deeper than the microlaterolog, which ensures that the mudcake has less effect but means that the proximity log is more often affected by the undisturbed zone.

The response of a logging measurement as a function of distance from the tool. The pseudogeometrical factor is normally radial, reflecting the response perpendicular to the tool. It can be a differential factor, which is the contribution to the signal at a particular distance, but is more normally integrated, which is the sum of all signals from the tool to a particular distance.The pseudogeometrical factor developed from the concept of the geometrical factor, and is expressed in the same way. For example, for a radial distance x from the tool, the integrated radial pseudogeometrical factor, Jx, can be written as: Jx = (Ux - Ut) / (Uxo - Ut)where Ut is the log reading of the undisturbed zone (or, alternatively, the reading with no invasion), Uxo is the log reading of the flushed zone (or, alternatively, the reading with infinite invasion), and Ux is the log reading with a step profile invasion to depth x. Unlike the geometrical factor, Jx depends on the values of both Uxo and Ut. Pseudogeometrical factors are a useful way to express the radial response (or vertical response) in typical conditions. The physics of each measurement determines how much Jx varies with Uxo and Ut.Pseudogeometrical factors are often used to express the response of nuclear and resistivity logs, but are not appropriate for acoustic and electromagnetic propagation logs (where the response is too dependent on the contrast in properties), or nuclear magnetic resonance logs (where the response is too localized).

A descriptive term for a fluid with shear-thinning characteristics that does not exhibit thixotropy. Most effective drilling fluids are shear thinning, although most also exhibit some gel-building characteristics. Pseudoplastic rheology, low viscosity at high shear rates and high viscosity at low shear rates, benefits several aspects of drilling-higher drilling rate and improved cuttings lifting. Bingham plastic fluids, power-law fluids and Herschel-Bulkley fluids fall in the psuedoplastic category of rheology.

A plot of real gas pseudopressure (pseudopotential) m(p) versus time function used to analyze gas-well drawdown and buildup tests. The use of the real gas pseudopressure linearizes the diffusion equation for gas flow. This form enables rigorous analysis over all pressure ranges. The pressure-squared plot can be used for low pressure (p < ~2000 psi), and pressure can be used to analyze gas-well tests at high pressure (p > ~3000 psi).

The ideal spontaneous potential (SP) that would be observed opposite a shaly, permeablebed if the SP currents were prevented from flowing. In the middle of a thick, permeable bed whose resistivity is not too high, the SP reads close to the pseudostatic spontaneous potential (PSP). In other conditions, however, the SP may be significantly less than the PSP. The PSP ignores other potential sources and assumes that a surrounding shale is a perfect cationic membrane. The ratio of the PSP to the static spontaneous potential is known as the SP reduction factor, alpha. Alpha is less than 1 and is a function of the shaliness, or cation-exchange capacity, within the sand. The higher this cation-exchange capacity, the larger the internal membrane potential. The latter has the opposite polarity to the liquid-junction potential and reduces the SP.The PSP, and alpha, are reduced when hydrocarbons are introduced into shaly sands, because the cation-exchange capacity in the sands is forced into a smaller conductive pore volume and therefore has a larger relative effect.

Behavior observed when a well reaches stabilizedproduction from a limited drainage volume. For constant-rate production, under pseudosteady state, the difference between the flowing wellbore pressure and the average reservoir pressure in the drainage volume is constant, and the pressure drawdown is a linear function of time, resulting in a unit slope in the log-log pressure derivative. The late-time buildup pressure will level off to the average reservoir pressure if the buildup duration is sufficient long, resulting in a sudden drop in the log-log pressure derivative. Pressure depletion occurs with continued pseudosteady-state production.

A phenomenon of relative seismic velocities of strata whereby a shallow layer or feature with a high seismic velocity (e.g., a salt layer or salt dome, or a carbonatereef) surrounded by rock with a lower seismic velocity causes what appears to be a structural high beneath it. After such features are correctly converted from time to depth, the apparent structural high is generally reduced in magnitude.

A slickline or coiled tubing tool used to retrieve temporary devices, such as plugs and flow-control equipment, from the wellbore. Pulling tools are available in a range of sizes and profiles and must be compatible with the equipment to be retrieved. A contingency release system in the pulling tool allows the tool to be released and retrieved if the equipment to be retrieved cannot be released.

A technique in which an ultrasonic transducer, in transmit mode, emits a high-frequencyacoustic pulse towards the borehole wall, where it is reflected back to the same transducer operating in receive mode. The measurement consists of the amplitude of the received signal, the time between emission and reception, and sometimes the full waveform received. Tools that use this technique either have multiple transducers, facing in different directions, or rotate the transducer while making measurements, thereby obtaining a full image of the borehole wall. Pulse-echo techniques are used in the borehole televiewer. In cased hole, the waveform is analyzed to give indications of cement-bond quality and casingcorrosion.

A wireline log of the yields of different elements in the formation, measured using induced gamma ray spectroscopy with a pulsed neutron generator. The elemental yields are derived from two intermediate results: the inelastic and the capture spectrum. The inelastic spectrum is the basis for the carbon-oxygen log, and can also give information on other elements. The capture spectrum depends on many elements, mainly hydrogen, silicon, calcium, iron, sulfur and chlorine. Since the elemental yields give information only on the relative concentration of elements, they are normally given as ratios, such as C/O, Cl/H, Si/(Si + Ca), H/(Si + Ca) and Fe/(Si + Ca). These ratios are indicators of oil, salinity, lithology, porosity and clay, respectively. To get absolute concentrations, it is necessary to calibrate to cores or, more often, use a model such as the oxide-closure model.The depth of investigation of the log is several inches into the formation. It can be run in open or cased hole. Pulsed neutron spectroscopy logs were introduced in the mid 1970s after a decade or more of investigation.

A measurement of the spectrum of gamma rays emitted by a formation bombarded by high-energy neutrons. Neutrons are emitted by a high-energy neutron generator (14.1 MeV). The neutrons interact with different nuclei, which may emit characteristic gamma rays through inelastic neutron scattering, fast-neutron reactions and neutron capture. When pulses from a neutron generator are used, it is possible to separate the different interactions in time after each neutron pulse. Inelastic and fast-neutron interactions occur very soon after the neutron burst, while most of the capture events occur later. The two types can therefore be separated to give a so-called inelastic spectrum and a capture spectrum. The spectra are analyzed either by counting gamma rays in windows placed at the main peaks for the elements concerned, or by comparison with spectral standards, or by combining the two (alpha processing).The resultant logs are known as pulsed neutron spectroscopy logs, the most common of which are the carbon-oxygen log and the elemental capture spectroscopy log.

(noun) A nuclear production logging measurement that uses a pulsed-neutron source to determine the fraction of oil, water, and gas present at each depth in a cased wellbore by exploiting the different hydrogen indices and neutron capture cross-sections of each fluid phase.

The cylinder of the downhole pump.

A condition affecting an operating pump whereby the pump space is not fully charged with fluid being pumped. Pump cavitation may result from inadequate or restricted supply or from the introduction of air or gas into the fluid stream. The effect of cavitation depends on the type of pump. However, in most cases, it is an undesirable condition that causes a reduction in pump efficiency and excessive wear or damage to pump components.

The arrangement of lines and valves used to direct and control fluid on a pumping unit. The manifold on the pump suction is generally known as the inlet or low-pressure manifold. The corresponding manifold located on the pump discharge is commonly known as the high-pressure or discharge manifold. In most cases, reference to the pump manifold relates to the high-pressure manifold.

The difference in hydrostatic head between the pump depth and the dynamic fluid level above the pump. The pump submergence is continuously monitored to adjust the pump flow rate and avoid a pump-off condition.

The relationship between actual pump displacement and the pump displacement under ideal conditions. The relationship can be expressed as percentage. A reduction in pump volumetric efficiency is an indication of an operational problem in the well. In sucker-rod pumps, the gas lock and gas interference phenomena can significantly reduce the volumetric efficiency of the pump.

A phenomenon produced when pump submergence into the fluid column is low. A pump-off situation will increase the gas intake, thus reducing the pump efficiency.

The ability of the slurry to be pumped. Pumpability is usually measured by the API thickening-time test.

A mobile high-pressure pumping unit commonly used for cementing or stimulation operations. Most pump units are configured with a high-pressure triplex pump and one or more centrifugal pumps to precharge the triplex pump and handle displacement fluids.

A document prepared to list the sequence, type and volume of fluids to be pumped during a specific treatment.

The total time required for pumping the cementslurry into the well, plus a safety factor. Pumping time can also be the time required to reach a consistency deemed to be unpumpable (generally 70 Bc) during an API thickening-time test.

A well produced by use of some kind of downhole pump. Pumps are required when the formationpressure is not sufficient to allow flowing production of fluids at the desired or necessary rate. The performance of well tests on pumping wells is always complicated by the presence of the pump, which often must be removed to take downhole pressure measurements. Downhole pressure measurements in pumping wells are usually made by measuring the rise in liquid level in the well. This is often accomplished by sonic devices, like well sounders, that measure the response time of sound waves bounced off the downhole liquid surface. Most oil wells are eventually put on pumps as pressure declines during production. The exceptions are in strong waterdrive reservoirs or in settings where pressure maintenance by gas or water injection is sufficient to maintain a high reservoir pressure.

Testing that is accomplished by measuring pressure in the annulus, or by pulling the pump and running a pressure gauge in the hole. The preferred method is usually to measure the pressure in the annulus if no packer is present. This is best done by monitoring the rise in fluid level with an echo-sounding device and calculating the bottomhole pressure by assuming a fluid density. Several excellent devices and associated services are available. Any time a well is shut in gradually, as is the case for pumping wells, some kind of multirate analysis is usually required to obtain acceptable results.

A phenomenon of relative seismic velocities of strata whereby a shallow layer or feature with a low seismic velocity (e.g., a shalediapir or a gas chimney) surrounded by rock with a higher seismic velocity causes what appears to be a structural low beneath it. After such features are converted from time to depth, the apparent structural low is generally reduced in magnitude. Hydrocarbon indicators can display velocity push-downs because the velocity of hydrocarbon is slower than that of rock.

A type of geochemical analysis in which a rock sample is subject to controlled heating in an inert gas to or past the point of generating hydrocarbons in order to assess its quality as a source rock, the abundance of organic material in it, its thermal maturity, and the quality of hydrocarbons it might generate or have generated. Pyrolysis breaks large hydrocarbon molecules into smaller molecules.This process is used to determine the quality of shale as a source rock and is instrumental in evaluating shale gas plays.

A mineral containing ferrous sulfide, FeS, that typically contains inclusions of free sulfur and other minerals. It is commonly present in shales, and may occur as a trace mineral in some barite ores. Pyrrhotite can liberate sulfides in alkaline muds, with adverse consequences for safety and corrosion.Reference:Binder GG, Carlton LA and Garrett RL: "Evaluating Barite as a Source of Soluble Carbonate and Sulfide Contamination in Drilling Fluids," Journal of Petroleum Technology 33, no. 12 (December 1981): 2371-2376.