Oil and Gas Terms Beginning with “B”

An abbreviation for oilfield barrel, a volume of 42 US gallons [0.16 m3].

An average or baseline measure of gas entrained in circulating mud. This baseline trend pertains to gas that is liberated downhole while drilling through a uniform lithologic interval at a constant rate of penetration. The gas is typically obtained from a suction line above the gas trap located immediately upstream of the shaleshaker screens, where the gas evolves out of the mud.Oil-base mud systems tend to produce higher background gas values than do water-base muds. Deviations from the background gas trend likely indicate changes in porosity or permeability, or changes in drilling conditions; any of which merits further investigation. A drift or gradual shift of the background gas trend toward higher values may indicate a slow gas influx into the mud column, which can eventually lead to a kick or blowout. When annotated on mud logs, background gas is usually abbreviated as BGG.

The lower portion of the drillstring, consisting of (from the bottom up in a vertical well) the bit, bit sub, a mud motor (in certain cases), stabilizers, drill collar, heavy-weight drillpipe, jarring devices ("jars") and crossovers for various threadforms. The bottomhole assembly must provide force for the bit to break the rock (weight on bit), survive a hostile mechanical environment and provide the driller with directional control of the well. Oftentimes the assembly includes a mud motor, directional drilling and measuring equipment, measurements-while-drilling tools, logging-while-drilling tools and other specialized devices. A simple BHA consisting of a bit, various crossovers, and drill collars may be relatively inexpensive (less than $100,000 US in 1999), while a complex one may cost ten or more times that amount.

The temperature of the circulating fluid (air, mud, cement or water) at the bottom of the wellbore after several hours of circulation. This temperature is lower than the bottomhole static temperature. Therefore, in extremely harsh environments, a component or fluid that would not ordinarily be suitable under bottomhole static conditions may be used with great care in circulating conditions. Similarly, a high-temperature well may be cooled down in an attempt to allow logging tools to function. The BHCT is also important in the design of operations to cement casing because the setting time for cement is temperature-dependent. The BHCT and bottomhole static temperature (BHST) are important parameters when placing large volumes of temperature-sensitive treatment fluids.

The pressure, usually measured in pounds per square inch (psi), at the bottom of the hole. This pressure may be calculated in a static, fluid-filled wellbore with the equation:BHP = MW * Depth * 0.052where BHP is the bottomhole pressure in pounds per square inch, MW is the mud weight in pounds per gallon, Depth is the true vertical depth in feet, and 0.052 is a conversion factor if these units of measure are used. For circulating wellbores, the BHP increases by the amount of fluid friction in the annulus. The BHP gradient should exceed the formationpressure gradient to avoid an influx of formation fluid into the wellbore.On the other hand, if BHP (including the added fluid friction pressure of a flowing fluid) is too high, a weak formation may fracture and cause a loss of wellbore fluids. The loss of fluid to one formation may be followed by the influx of fluid from another formation.

The temperature of the undisturbed formation at the final depth in a well. The formation cools during drilling and most of the cooling dissipates after about 24 hours of static conditions, although it is theoretically impossible for the temperature to return to undisturbed conditions. This temperature is measured under static conditions after sufficient time has elapsed to negate any effects from circulating fluids. Tables, charts and computer routines are used to predict BHST as functions of depth, geographic area and various time functions. The BHST is generally higher than the bottomhole circulating temperature, and can be an important factor when using temperature-sensitive tools or treatments.

The temperature in the borehole at total depth at the time it is measured. In log interpretation, the bottom hole temperature (BHT) is taken as the maximum recorded temperature during a loggingrun, or preferably the last of series of runs during the same operation. BHT is the temperature used for the interpretation of logs at total depth. Farther up the hole, the correct temperature is calculated by assuming a certain temperature gradient. The BHT lies between the bottomhole circulating temperature (BHCT) and the bottomhole static temperature (BHST).

Abbreviation for barrels of liquid per day, usually used in reference to total production of oil and water from a well. The volume of a barrel is equivalent to 42 US gallons.

A permanently fixed marker cited in surveying, such as a concrete block or steel plate, with an inscription of location and elevation.

The amount of oxygen consumed by biodegradation processes during a standardized test. The test usually involves degradation of organic matter in a discarded waste or an effluent.

A large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. By closing this valve (usually operated remotely via hydraulic actuators), the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to open the BOP and retain pressure control of the formation. BOPs come in a variety of styles, sizes and pressure ratings. Some can effectively close over an open wellbore, some are designed to seal around tubular components in the well (drillpipe, casing or tubing) and others are fitted with hardened steel shearing surfaces that can actually cut through drillpipe. Since BOPs are critically important to the safety of the crew, the rig and the wellbore itself, BOPs are inspected, tested and refurbished at regular intervals determined by a combination of risk assessment, local practice, well type and legal requirements. BOP tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems.

A set of two or more BOPs used to ensure pressure control of a well. A typical stack might consist of one to six ram-type preventers and, optionally, one or two annular-type preventers. A typical stack configuration has the ram preventers on the bottom and the annular preventers at the top. The configuration of the stack preventers is optimized to provide maximum pressure integrity, safety and flexibility in the event of a well control incident. For example, in a multiple ram configuration, one set of rams might be fitted to close on 5-in. diameter drillpipe, another set configured for 4 1/2-in. drillpipe, a third fitted with blind rams to close on the openhole and a fourth fitted with a shear ram that can cut and hang-off the drillpipe as a last resort. It is common to have an annular preventer or two on the top of the stack since annulars can be closed over a wide range of tubular sizes and the openhole, but are typically not rated for pressures as high as ram preventers. The BOP stack also includes various spools, adapters and piping outlets to permit the circulation of wellbore fluids under pressure in the event of a well control incident.

Abbreviation for barrels of oil per day, a common unit of measurement for volume of crude oil. The volume of a barrel is equivalent to 42 US gallons.

Abbreviation for basic sediment and water. BS&W is measured from a liquid sample of the production stream. It includes free water, sediment and emulsion and is measured as a volume percentage of the production stream.

Abbreviation for British thermal unit.

Describing the amount (in percent) of a material added to cement when the material is added based on the total amount of a specific blend, often abbreviated as BWOB.

Describing the amount (in percent) of a material added to cement, and is often abbreviated as BWOC. BWOC is the method used to describe the amount of most additives in the dry form

Describing the amount (in percent) of a material added to a cementslurry based on the weight of water used to mix the slurry. Commonly abbreviated as BWOW, this convention normally is used only for salt [NaCl].

Abbreviation for barrels of water per day, a common unit of measurement for the daily volume of produced water. The volume of a barrel is equivalent to 42 US gallons.

Unexpected reverse motion of the tongs, left on a pipe or collar, during the pipe spinning operation.

The end of the bale bars that form an enclosed eye.

Long, heavy steel bars with an eye on each end connecting traveling blocks to elevators.

An inference or deduction made using Bayes' theorem. Bayesian inference also is used in performing stochastic analyses of geological scenarios or building stochastic models of geological environments.

A method of updating distributions that requires that prior distributions of the required geological characteristics are defined and that calculation of the posterior distributions be based on an exact stochastic model.

A probability based on Bayes' theorem of interdependent events occurring interdependently.

The pumpability or consistency of a slurry, measured in Bearden units of consistency (Bc), a dimensionless quantity with no direct conversion factor to more common units of viscosity

Abbreviation for billion cubic feet, a unit of measurement for large volumes of natural gas.

Abbreviation for billion cubic feet per day, a unit of measurement for large production rates of natural gas.

The pumpability or consistency of a slurry, measured in Bearden units of consistency (Bc), a dimensionless quantity with no direct conversion factor to more common units of viscosity.

The 0 to 12 scale for measurement of wind strength according to its effect on objects such as trees, flags and water established by Admiral Francis Beaufort (1774 to 1857). According to the Beaufort scale, at wind speeds below 1 knot or 1 km/hr, seas are calm. Whitecaps on water and blowing dust and leaves correspond to a Beaufort number of 4, with winds of 11 to 16 knots [20 to 28 km/hr]. Hurricane-force winds, greater than 64 knots [> 118 km/hr], have a Beaufort number of 12.

A two-parameterrheologicalmodel widely used in the drilling fluids industry to describe flow characteristics of many types of muds. It can be described mathematically as follows: Fluids obeying this model are called Bingham plastic fluids and exhibit a linear shear-stress, shear-rate behavior after an initial shear stress threshold has been reached. Plastic viscosity (PV) is the slope of the line and yield point (YP) is the threshold stress. PV should be as low as possible for fast drilling and is best achieved by minimizing colloidal solids. YP must be high enough to carry cuttings out of the hole, but not so large as to create excessive pump pressure when starting mud flow. YP is adjusted by judicious choices of mud treatments. The direct-indicating rotational rheometer was specifically designed to apply the Bingham plastic fluid model.

A theory for acoustic propagation in a porous and elastic medium developed by M.A. Biot. Compressional and shear velocities can be calculated by standard elastic theory from the composite density, shear and bulk modulus of the total rock. The problem is how to determine these from the properties of the constituent parts. Biot showed that the composite properties could be determined from the porosity and the elastic properties (density and moduli) of the fluid, the solid material, and the empty rock skeleton, or framework. To account for different frequencies of propagation, it is also necessary to know the frequency, the permeability of the rock, the viscosity of the fluid and a coefficient for the inertial drag between skeleton and fluid.Unlike the Gassmann model, the Biot theory takes into account frequency variations, and allows for relative motion between fluid and rock framework. As a result, it predicts some of the observed changes in velocity with frequency, as well as the critical frequency below which the Gassmann model is valid. It also predicts the existence of a so-called slow wave in addition to the shear wave and the compressional, or fast wave. The slow wave arises when the fluid and the skeleton move 1800 out-of-phase with each other. Its velocity is related to fluid mobility, but unfortunately has been observed only in the laboratory, not on logs. At logging frequencies, it degenerates into a diffusion phenomenon rather than a wave, and is apparently too highly attenuated to be observed in real rocks. However, in permeable formations, the Stoneley wave couples into the slow wave, causing the attenuation and dispersion that allow the measurement of Stoneley permeability.The full Biot theory is used mainly to analyze laboratory data. For practical log interpretation, it is more common to use the simpler Gassmann model.Reference:See Biot MA: Theory of Propagation of Elastic Waves in a Fluid-Saturated Porous Solid: I Low Frequency Range, Journal of the Acoustical Society of America 28, (1956):168-178. Biot MA: Theory of Propagation of Elastic Waves in a Fluid-Saturated Porous Solid: II Higher Frequency Range,Journal of the Acoustical Society of America 28, (1956): 179-191.

The vertical storage area in the derrick for tubular stands, with rows of mounting pegs for each stand referred to as alligator teeth.

A crossover sub inserted between the drill collar and the bit.

The particle size or fineness of a cement in cm2/g or m2/kg, usually determined from air permeability tests using a device known as a Blaine permeameter. Fineness affects the hydration rate (setting) and the requirements for the amounts of water, retarder and dispersant.

The stacked arrangement of well control equipment including annular preventers, ram preventers, diverter spools, valves, and nipples. Also known as BOP Stack.

A closed vessel in which water or other fluid is heated for various processes.

Bolts placed through a pin that prevents the pin from sliding out of the hole.

One of a number of possible distributions that may occur when the results of events are plotted. Boltzmann distributions were originally described from theoretical consideration on the probable interactions of molecules. It has been used in simulation of annealing and can be used for studying perturbations in geostatistical models.

A dimensionless group used in analysis of fluid flow that characterizes the ratio of gravitational forces to surface or interfacial tension forces. It is usually denoted Nb in the oil field and Bo in chemical engineering. A value of Nb 1 implies gravitational forces dominate over interfacial forces.Bond number equation:

The development of a reservoirmodel by the use of objects. Reservoir models may be developed by adding together a series of objects (such as channel belts) in a fashion that honors the well data (logs, cores, etc.) and satisfies all the geostatistical requirements of the model. Such models may be used to simulate the behavior of the fluids in a reservoir.

A method of analyzing the response of an inductionlogging tool that considers the contribution of each element of the formation as a perturbation from the average background conductivity. The development of the solution is similar to the Born approximation in quantum mechanics, since the latter also involves a single scattering. The Born response is valid for modest formation contrasts. The zero-conductivity Born response is identical to the geometrical factor.

The portion of the drilling assembly below the drill pipe, potentially including bits, collars, jars, and stabilizers. Also known as BHA.

The remaining value of gravitational attraction after accounting for the theoretical gravitational attraction at the point of measurement, latitude, elevation, the Bouguer correction and the free-air correction (which compensates for height above sea level assuming there is only air between the measurement station and sea level). This anomaly is named for Pierre Bouguer, a French mathematician (1698 to 1758) who demonstrated that gravitational attraction decreases with altitude.

The adjustment to a measurement of gravitational acceleration to account for elevation and the density of rock between the measurement station and a reference level. It can be expressed mathematically as the product of the density of the rock, the height relative to sea level or another reference, and a constant, in units of mGal:Strictly interpreted, the Bouguer correction is added to the known value of gravity at the reference station to predict the value of gravity at the measurement level. The difference between the actual value and the predicted value is the gravity anomaly, which results from differences in density between the actual Earth and reference model anywhere below the measurement station.

A characteristic sequence of sedimentary structures occurring in sedimentary rocks deposited in areas of deep water sedimentation by turbidity currents, which form deposits called turbidites. In theory, a complete Bouma sequence comprises sediments that fine upwards, consisting of a lowermost layer of coarse, chaotic clastic sediments deposited under conditions of high depositional energy overlain by successively finer grained and better stratified sediments like sands and muds deposited under calmer conditions that are labeled as Units A though E. In practice, however, the chaotic, high-energy nature of turbidite deposition can alter or remove underlying sediments so that incomplete sequences of sediments typically remain preserved.

The female end of a tool joint with internal threads inside.

A principle of physics stating that the product of pressure and volume divided by the temperature is a constant for an ideal gas. It is a good approximation for many real gases, such as helium, over reasonable ranges of temperature and pressure.

A technique for measuring the grain volume of a core sample by observing the change in pressure of helium introduced into a chamber containing the sample. The rock sample is placed in a chamber of known volume. Helium is held in a reference chamber at known volume and pressure, typically 100 to 200 psi [689 to 1379 kPa]. The two chambers are connected, causing the helium to drop in pressure as it fills the sample chamber and the pores in the sample. The only volume not filled is the grain volume and the isolated pores. Neglecting the latter, the grain volume can then be calculated from Boyle's Law using the pressure before and after connecting the chambers and the chamber volumes.

A technique for measuring the pore volume of a core sample by observing the change in pressure of helium introduced into the pore space. The rock sample is held in a core holder whose internal walls are elastomers, so that the only void space is the internal pore volume. With a suitable holder, the sample can be held under a confining stress. Helium is held in a reference cell at known volume and pressure, typically 100 to 200 psi [689 to 1379 kPa]. The helium is introduced to the core sample, dropping in pressure as it fills the connected pore space. The effective pore volume is obtained from Boyle's Law using the pressure before and after introduction of helium, and the reference volume.

The part of the brake mechanism consisting of a flexible steel band lined with a material that grips a drum.

Large wrench-like tool suspended from the derrick on the mud tank side of the rotary table for breaking torque.

A cable used to pull the derrick into the upright position.

A system for color-coding three-dimensional information. This system is used in wireline log analysis to provide color shading in which the final color is determined by the values of three curves. One curve dictates the intensity of red, a second the intensity of green, and the third the intensity of blue. The final resulting color is the result of the three input curves. The input curves may be raw curves from the field or computed curves. When used for correlation work on cross sections, the curves must have been normalized to remove the effects of incorrect calibrations and borehole problems.Reference:Doveton JH: Geologic Log Analysis Using Computer Methods, AAPG Computer Applications in Geology, No. 2. AAPG, Tulsa, Oklahoma, USA (1994): 39-41.

A measure of heat energy required to raise the temperature of one pound of water by one degree Fahrenheit. British thermal unit is abbreviated as BTU.

A cone-and-plate rheometer designed to measure viscosity of non-Newtonian fluids at low shear rates and with more accuracy than is attainable with a 6-speed, direct-indicating viscometer. Such low shear-rate data are needed for designing muds with improved hole-cleaning properties and to minimize sag of weighting material. (Brookfield is a mark of Brookfield Engineering Laboratories, Inc.)

The motion of atoms and molecules in fluids due to the temperature of the fluid. The motion appears to be random, but is described by the relationships derived by Brown.

Protective timbers or rubber blocks positioned below the crown to act as a cushion.

A tool used to hook into each table bushing insert to remove or set them in the rotary table.

A set of split wedged inserts that fit into the rotary table that help force the slips to grip the tubular.

To unscrew drillstring components downhole. The drillstring, including drillpipe and the bottomhole assembly, are coupled by various threadforms known as connections, or tool joints. Often when a drillstring becomes stuck it is necessary to "back off" the string as deep as possible to recover as much of the string as possible. To facilitate the fishing or recovery operation, the backoff is usually accomplished by applying reverse torque and detonating an explosive charge inside a selected threaded connection. The force of the explosion enlarges the female (outer) thread enough that the threaded connection unscrews instantly. A torqueless backoff may be performed as well. In that case, tension is applied, and the threads slide by each other without turning when the explosive detonates. Backing off can also occur unintentionally.

The pressure within a system caused by fluid friction or an induced resistance to flow through the system. Most process facilities require a minimum system pressure to operate efficiently. The necessary back-pressure is often created and controlled by a valve that is set to operate under the desired range of conditions.

A type of check valve, typically installed in the tubing hanger, to isolate the production tubing. The back-pressure valve is designed to hold pressure from below yet enable fluids to be pumped from above, as may be required for well-control purposes.

A method for reconstructing the location and shape of the wave at an earlier time using the wave equation.

A modeling technique to assess the geologic history of rock layers through the use of geologic cross sections or seismic sections. Removal of the youngest layers of rock at the top of the section allows restoration of the underlying layers to their initial, undisturbed configurations. Successively older layers can be removed sequentially to further assess the effects of compaction, development of geologic structures and other processes on an area.

To hold one end of a threaded connection while the other is turned to make up the joint. To ensure a secure connection, many types of threaded joints are made up to specific torque requirements in oil- and gas-well applications. This process requires the controlled application of force to the rotating component and a means of stabilizing and securing the corresponding stationary component to which it is being connected.

A supporting ring used with an O-ring, or similar seal, to prevent extrusion of the seal material under high differential pressures or excess wear under dynamic sealing conditions

The right to receive a reversionary interest at some future time, upon fulfillment of contractually specified conditions. This clause allows a lease-owner, lessee or a nonparticipating partner to reserve the option to participate in a well after it has produced enough to pay the operators expenses of drilling and completing that well. This clause is typically used in farmout agreements to convert the overriding royalty interest of a lease-owner, lessee or nonparticipating partner into a working interest upon payout of the well. When the election to convert the overriding royalty to working interest takes place, it is known as a back-in after payout (BIAPO).

The pressure within a system caused by fluid friction or an induced resistance to flow through the system. Most process facilities require a minimum system pressure to operate efficiently. The necessary back-pressure is often created and controlled by a valve that is set to operate under the desired range of conditions.

A type of check valve, typically installed in the tubing hanger, to isolate the production tubing. The back-pressure valve is designed to hold pressure from below yet enable fluids to be pumped from above, as may be required for well-control purposes.

A method for reconstructing the location and shape of the wave at an earlier time using the wave equation.

A modeling technique to assess the geologic history of rock layers through the use of geologic cross sections or seismic sections. Removal of the youngest layers of rock at the top of the section allows restoration of the underlying layers to their initial, undisturbed configurations. Successively older layers can be removed sequentially to further assess the effects of compaction, development of geologic structures and other processes on an area.

A supporting ring used with an O-ring, or similar seal, to prevent extrusion of the seal material under high differential pressures or excess wear under dynamic sealing conditions.

Fluid flow in the borehole from one zone into another in response to pressure differences between the zones. Any time the wellbore pressure rises above the average pressure in any zone, backflow will occur. Analysis of buildup tests involving backflow is either impossible or extremely difficult and usually requires expert input to determine useful information from such tests.

An average or baseline measure of gas entrained in circulating mud. This baseline trend pertains to gas that is liberated downhole while drilling through a uniform lithologic interval at a constant rate of penetration. The gas is typically obtained from a suction line above the gas trap located immediately upstream of the shale shaker screens, where the gas evolves out of the mud.Oil-base mud systems tend to produce higher background gas values than do water-base muds. Deviations from the background gas trend likely indicate changes in porosity or permeability, or changes in drilling conditions; any of which merits further investigation. A drift or gradual shift of the background gas trend toward higher values may indicate a slow gas influx into the mud column, which can eventually lead to a kick or blowout. When annotated on mud logs, background gas is usually abbreviated as BGG.

To unscrew drillstring components downhole. The drillstring, including drillpipe and the bottomhole assembly, are coupled by various threadforms known as connections, or tool joints. Often when a drillstring becomes stuck it is necessary to "back off" the string as deep as possible to recover as much of the string as possible. To facilitate the fishing or recovery operation, the backoff is usually accomplished by applying reverse torque and detonating an explosive charge inside a selected threaded connection. The force of the explosion enlarges the female (outer) thread enough that the threaded connection unscrews instantly. A torqueless backoff may be performed as well. In that case, tension is applied, and the threads slide by each other without turning when the explosive detonates. Backing off can also occur unintentionally. Synonyms: break out

Pressure registered on equipment or devices when fluid flows through.

A reflection phenomenon of energy in which a nonreflective surface, which is a surface that does not reflect energy coherently, randomly scatters energy. No coherent reflected energy can be identified and the energy is scattered in all directions, including back in the direction from which it came. For example, light can be scattered or redistributed by rough, nonreflective surfaces.

A term used to describe the annulus surrounding a production tubing string above the production packer.

An extra curve on a log, designed to appear when the standard curve goes off track. For example, if the standard gamma ray curve is presented on a scale of 0 to 200 gAPI units, the backup curve may be scaled from 200 to 400 gAPI units. Alternatively, if the standard resistivity log is presented on a scale of 0 to 50 ohm-m, the backup curve might be presented on a scale of 0 to 500 ohm-m in the same track but be blanked off for readings below 50 ohm-m. The backup curve usually has the same coding as the standard curve but a different line weight.

A laboratory test to determine the phase envelope between oil and enriched gas. The test is conducted by equilibrating an oil sample several times with fresh samples of gas. Intermediate components are stripped from the gas by multiple contacts with the oil. The test also indicates how many contacts are required before the oil with added intermediate components becomes miscible with the gas. The molar ratios at each contact step are typically designed using PVT simulation software that incorporates the fluid composition from the previous contact.

An additive that kills bacteria. Bactericides are commonly used in water muds containing natural starches and gums that are especially vulnerable to bacterial attack. Bactericide choices are limited and care must be taken to find those that are effective yet approved by governments and by company policy.Bactericides, also called biocides, can be used to control sulfate-reducing bacteria, slime-forming bacteria, iron-oxidizing bacteria and bacteria that attacks polymers in fracture and secondary recovery fluids. In polymers, the degradation of the fluid is controlled, thus avoiding the formation of a large biomass, which could plug the formation and reduce permeability.

A borehole that is not to gauge or is rugose. The term usually refers to the detrimental effect that such a borehole has on the response of logging measurements, in particular pad tools like the density or micro-resistivity. The existence of bad hole is usually determined by a caliper log and on various secondary measurements such as delta rho.

The point at which the forces acting on a tubing string suspended in a live wellbore are equal. Under these conditions, the weight of the tubing string is balanced by the wellbore pressure acting to expel the string from the wellbore. The friction caused by the tubing string passing through the stripper or wellhead sealing device acts to extend the interval over which the balance point is apparent.

An oil-base mud in which the activity, or vapor pressure, of the brinephase is balanced with that of the formations drilled. Although long shale sections may not have a constant value for vapor pressure, aw, the oil mud will adjust osmotically to achieve an "average" aw value. Dynamic (autopilot) balance of mud salinity and drilled shales is maintained because as water moves into or out of the mud, it also moves out of or into the shale. As water transfer continues during drilling, the mud's water phase will be either diluted or concentrated in CaCl2 as needed to match the average aw value of the shale section and cuttings exposed to the mud.Reference:Chenevert ME: "Shale Control With Balanced-Activity Oil-Continuous Muds," Journal of Petroleum Technology 33, no. 11 (November 1970): 1370-1378.

An array induction whose transmitters and receivers are arranged to produce a null reading in free space, that is, which has the mutual signal balanced to zero.

A plug of cement or similar material placed as a slurry in a specific location within the wellbore and which has set to provide a means of pressure isolation or mechanical platform. For correct placement, the volume of slurry and the displacement fluid must be carefully calculated and measured. The correct volume ensures that the column of fluid in the tubing string is balanced by the column of fluid in the annulus.

An oil-base mud in which the activity, or vapor pressure, of the brine phase is balanced with that of the formations drilled. Although long shale sections may not have a constant value for vapor pressure, aw, the oil mud will adjust osmotically to achieve an "average" aw value. Dynamic (autopilot) balance of mud salinity and drilled shales is maintained because as water moves into or out of the mud, it also moves out of or into the shale. As water transfer continues during drilling, the mud's water phase will be either diluted or concentrated in CaCl2 as needed to match the average aw value of the shale section and cuttings exposed to the mud.Reference:Chenevert ME: "Shale Control With Balanced-Activity Oil-Continuous Muds," Journal of Petroleum Technology 33, no. 11 (November 1970): 1370-1378.

A downhole device or assembly used to catch and retain balls used to actuate ball-operated tools or equipment. Following activation, some ball-operated tools incorporate a means of ejecting the activation ball to regain a fullbore flow path. In such cases, the ball can be retained in a ball catcher.

The device used to inject ball sealers into the treatment fluid as it is pumped through the surface treating lines.

Describing a mechanism or system that is actuated by a ball that is dropped or pumped through the tubing string. Once located on a landing seat, the tool mechanism is generally actuated by hydraulic pressure.

Small spheres designed to seal perforations that are accepting the most fluid, thereby diverting reservoir treatments to other portions of the target zone. Ball sealers are incorporated into the treatment fluid and pumped with it. The effectiveness of this type of mechanical diversion to keep the balls in place is strongly dependent on the differential pressure across the perforation and the geometry of the perforation itself.

Describing a mechanism or system that is actuated by a ball that is dropped or pumped through the tubing string. Once located on a landing seat, the tool mechanism is generally actuated by hydraulic pressure.

A condition that may occur during ball diversion treatments in which all open perforations capable of receiving fluid are sealed. Ballout is signified by a rapid increase in treating pressure. Maintaining the treatment pressure may result in the breakdown and subsequent treatment of plugged perforations. If no further injection is possible, the pressure must be released to unseat the ball sealers, at which time the treatment will be terminated.

A range of frequencies or wavelengths. Audible frequencies of sound and visible wavelengths of light are examples of bands. In seismic data, band-pass frequencies are within the limits of a specific filter, while band-reject frequencies exceed the acceptable range of frequencies.

A function or time series whose Fourier transform is restricted to a finite range of frequencies or wavelengths.

Frequencies within the acceptable limits of a filter. The term is commonly used as an adjective, as in "band-pass filter," to denote a filter that passes a range of frequencies unaltered while rejecting frequencies outside the range.

Frequencies beyond the limits of a filter.

A function or time series whose Fourier transform is restricted to a finite range of frequencies or wavelengths.

Frequencies within the acceptable limits of a filter. The term is commonly used as an adjective, as in "band-pass filter," to denote a filter that passes a range of frequencies unaltered while rejecting frequencies outside the range.

Frequencies beyond the limits of a filter.

A technique in which several perforating guns are run on a single trip into the well, and then all are fired simultaneously.

Referring to openhole or without casing, as in barefoot completion or barefoot drillstem test.

(noun) A well completion method in which the production interval is left as open hole without casing, liner, or screen across the producing formation. Barefoot completions are typically employed in competent, consolidated formations where the rock is mechanically stable and sand production is not anticipated.

A dense mineral comprising barium sulfate [BaSO4]. Commonly used as a weighting agent for all types of drilling fluids, barites are mined in many areas worldwide and shipped as ore to grinding plants in strategic locations, where API specifies grinding to a particle size of 3 to74 microns. Pure barium sulfate has a specific gravity of 4.50 g/cm3, but drilling-grade barite is expected to have a specific gravity of at least 4.20 g/cm3 to meet API specifications. Contaminants in barite, such as cement, siderite, pyrrhotite, gypsum and anhydrite, can cause problems in certain mud systems and should be evaluated in any quality assurance program for drilling-mud additives.

A plug made from barite weighting materials that is placed at the bottom of a wellbore. Unlike a cement plug, the settled solids do not set solid, yet a barite plug can provide effective and low-cost pressure isolation. A barite plug is relatively easy to remove and is often used as a temporary facility for pressure isolation or as a platform enabling the accurate placement of treatments above the plug.

A volume of 350 cm3. In mud laboratory experiments, 350 cm3 is the volume chosen to represent 42 US gallons (1 oilfield barrel) [6.6 m3], so that 1.0 gram mass represents 1.0 lbm. This is a convenient concept for mud technicians to use when mixing or pilot-testing mud samples. For example, in preparing a mud formulation or for pilot-testing purposes, adding 1.0 grams to 350 cm3 of fluid is the experimental equivalent of adding 1.0 lb to 42 gallons (1.0 bbl) of fluid.

A small pump with an extended suction duct that is designed to pump fluid from barrels. Barrel pumps are commonly used to decant liquid additives during the preparation of treatment fluids at the wellsite.

A volume of fluid that refers to the daily total production of oil and water from a well. The volume of a barrel is equivalent to 42 US gallons, abbreviated BLPD.

A common unit of measurement for the daily volume of crude oil produced by a well or from a field. The volume of a barrel is equivalent to 42 US gallons, abbreviated BOPD.

A common unit of measurement for the volume of water produced each day by a well or in a field. The volume of a barrel is equivalent to 42 US gallons, abbreviated BWPD.

(noun) An alternate spelling of barite (BaSO₄), a dense mineral with a specific gravity of approximately 4.2 that is ground to a fine powder and used as a weighting agent in drilling fluids to increase mud density and maintain hydrostatic pressure control over formation pressures during drilling operations.

The log used as the reference for depths in the well. Each log may record formation features at slightly different depths due to their different response and the difficulty of aligning depths. It is therefore important to select one log to which the other logs are depth matched, and which is used as the reference for well-to-well correlation and mechanical operations such as perforating. The gamma ray is most often used as the base log since it can be recorded in both open and cased holes.

A map on which primary data and interpretations can be plotted. A base map typically includes locations of lease or concession boundaries, wells, seismic survey points and other cultural data such as buildings and roads, with a geographic reference such as latitude and longitude or Universal Transverse Mercator (UTM) grid information. Geologists use topographic maps as base maps for construction of surface geologic maps. Geophysicists typically use shot point maps, which show the orientations of seismic lines and the specific points at which seismic data were acquired, to display interpretations of seismic data. In the field, geologists can use a plane table and alidade to construct a base map.

The lower boundary of the near-surface, low-velocity zone in which rocks are physically, chemically or biologically broken down, in some cases coincident with a water table. Static corrections to seismic data can compensate for the low velocity of the weathered layer in comparison with the higher-velocity strata below.

A conventional cementslurry used as the cementitious component of a foamed cement slurry.

A reference location for a survey, or a survey point whose measured values of a given parameter of interest are understood and can be used to normalize other survey points. Accurate knowledge of base stations is critical in gravity and magnetic surveying.

The original survey of a set of surveys covering the same area but acquired over a period of time. In four-dimensional seismic data, it is the first seismic survey, which is then compared to subsequent surveys.

The rocklayer below which economic hydrocarbon reservoirs are not expected to be found, sometimes called economic basement. Basement is usually older, deformed igneous or metamorphic rocks, which seldom develops the porosity and permeability necessary to serve as a hydrocarbon reservoir, and below which sedimentary rocks are not common. Basement rocks typically have different density, acoustic velocity, and magnetic properties from overlying rocks.

A depression in the crust of the Earth, caused by plate tectonic activity and subsidence, in which sediments accumulate. Sedimentary basins vary from bowl-shaped to elongated troughs. Basins can be bounded by faults. Rift basins are commonly symmetrical; basins along continental margins tend to be asymmetrical. If rich hydrocarbon source rocks occur in combination with appropriate depth and duration of burial, then a petroleum system can develop within the basin.Most basins contain some amount of shale, thus providing opportunities for shale gasexploration and production.

A downhole device or tool component designed to catch debris or objects, such as balls, darts or plugs dropped to actuate downhole equipment or tools.

A device for measuring in situ the velocity of fluid flow in a production or injection well in which the flow is diverted through the spinner by a set of metal vanes, or petals. The vanes are closed while running in the hole, and then opened with the tool stationary at the measurement depth. The petals do not seal completely against each other or against the side of the hole, so that not all the fluid is diverted. A type of diverter flowmeter, the petal basket design has generally been replaced since the late 1980s by the inflatable diverter and other designs.

A vessel and mixing system used to prepare treatment fluids. A batch mixer is generally equipped with a means of adding dry and liquid chemicals, an agitation or circulation system and a manifold system to deliver the prepared fluid to storage tanks or treating pumps.

The pumping of a specific amount of treatment fluid, such as cementslurry, stimulation fluid, well completion fluid or chemical corrosion inhibitor.In corrosion control, there are several batch-treating techniques, such as tubing displacement and standard batch treatments, which are used to place the corrosion inhibitor in an oil or gas well.

Pertaining to the environment of deposition and the organisms of the ocean between depths of 200 m [656 ft], the edge of the continental shelf, and 2000 m [6560 ft]. The bathyal environment is intermediate between the neritic environment and the abyss.

The installation of similar or identical units of equipment in a group, such as a separator battery, header battery, filter battery or tank battery.

A portion of land that contains separators, treaters, dehydrators, storage tanks, pumps, compressors and other surface equipment in which fluids coming from a well are separated, measured or stored.

A small, radioactive plastic sphere that is insoluble and used to make a tracer-loss measurement. The bead is designed to have the same density as the injection fluid so that it travels with the fluid when it is placed in the flow stream of an injection well. However, the bead does not enter the formation. It remains on the rock face in openhole, or within the perforation channel in cased hole, where it can be detected by a gamma ray log. A high radioactivity opposite a perforation indicates a large number of beads and hence a high injectivity. The technique was used mainly in the 1960s and 1970s.

A fixed choke or a choke with an adjustable needle, sleeve or plate that can be changed to adjust the flow rate. The flow rate from a well is limited to conserve reservoir energy, decrease friction forces and improve production efficiency and prevent development of conditions that can reduce ultimate recovery. A high rate of fluid can generate a drastic cooling effect near the wellbore with the precipitation of scales and paraffins as well as a reduction of the oil relative permeability because of an increase in gas saturation.

(noun) A surface-mounted reciprocating artificial lift system, also known as a sucker rod pump or pumpjack, that uses a walking beam mechanism driven by a prime mover to impart an up-and-down motion to a string of sucker rods connected to a downhole plunger pump, lifting reservoir fluids to the surface.

A fixed choke or a choke with an adjustable needle, sleeve or plate that can be changed to adjust the flow rate.

A fixed choke used to control the flow of fluids, usually mounted on or close to the Christmas tree. A bean choke contains a replaceable insert, or bean, made from hardened steel or similar durable material. The insert is manufactured with a precise diameter hole that forms the choke through which all fluids must pass. Choke inserts are available in a complete range of sizes, generally identified by choke diameter stated in 64ths of an inch; for example, a "32 bean" is equivalent to a 1/2-in. choke diameter.

A layer of sediment or sedimentaryrock, or stratum. A bed is the smallest stratigraphic unit, generally a centimeter or more in thickness. To be labeled a bed, the stratum must be distinguishable from adjacent beds.

The thickness of a layer or stratum of sedimentaryrock measured perpendicular to its lateral extent, presuming deposition on a horizontal surface. Because sediment deposition can occur on inclined surfaces, apparent or measured bed thickness might differ from true bed thickness. The thickness of a given bed often varies along its extent.

The first layer of coiled tubing, slickline or wireline to be wound on the core of a reel drum or spool. The bed wrap helps secure the tubing string or slickline to the reel core and provides the foundation upon which subsequent wraps are laid as the drum is filled. A neat and secure bed wrap is necessary for proper spooling that will allow the drum to hold the maximum capacity without damaging the string.

Solid rock either exposed at the surface or situated below surface soil, unconsolidated sediments and weathered rock.

The unit of measurement to describe or compare the intensity of acoustic or electrical signal, named for American inventor Alexander Graham Bell (1847 to 1922). Measurements are typically given in tenths of a bel, or decibels. The logarithm of the ratio of the sound or signal to a standard provides the decibel measurement. Sounds on the order of one decibel are barely audible to humans but can cause pain when on the order of 1012 decibels. The symbol for the unit is B, but dB is the standard unit.

An enlarged pipe at the top of a casing string that serves as a funnel to guide drilling tools into the top of a well. The bell nipple is usually fitted with a side outlet to permit drilling fluids to flow back to the surface mud treating equipment through another inclined pipe called a flowline.

A condition in deviated wellbores in which an additional friction component is applied as the slickline, wireline or coiled tubing is drawn to the inside radius of the curve. The effect is largely dependent on the load on the string, with the resultant friction forces being of most influence when high loads are encountered under static or slow-moving conditions.

A standard against which the performance of processes are measured.

Chemical treatment or mechanical processes that improve a mineral or ore for its designed use. For example, barite and bentonite clay minerals are beneficiated in order to help them meet certain specifications for use in drilling fluids.Reference:Garrett RL: "Quality Requirements for Industrial Minerals Used in Drilling Fluids," Mining Engineering 39, no. 11 (November 1987): 1011-1016.

Pertaining to the environment and conditions of organisms living at the water bottom, or benthos. Also called benthonic.

A claymineral that is composed principally of three-layer clays, such as montmorillonite, and widely used as a mud additive for viscosity and filtration control. Commercial bentonite ores vary widely in amount and quality of the swelling clay, sodium montmorillonite. Ores of lower quality, those with more calcium-type montmorillonite, are treated during grinding by adding one or more of the following: sodium carbonate, long-chain synthetic polymers, carboxymethylcellulose (CMC), starch or polyphosphates. These help make the final product meet quality specifications. Unfortunately, the additives may not remain effective in "the real mud world" when in use at the rig due to hardness ions in the water, high temperature, bacterial attack, mechanical shear-degradation and other factors that can render these additives ineffective.

An adjustment of the relative positive and negative excursions of reflections during seismic processing by bulk shifting the null point, or baseline, of the data to emphasize peaks at the expense of troughs or vice versa. Some authors describe bias as a systematic distortion of seismic data to achieve greater continuity.

A technique used in the assembly of coiled tubing strings at the manufacturing plant. Prior to being formed, the string is assembled from flat steel strips joined by a bias weld that is angled across the strip joint at 45 degrees. When the tubing string is milled, the helical weld form provides enhanced characteristics of the tube at the weld site. These are significantly better than those achievable with the alternative butt weld technique.

A compound containing the bicarbonate ion [HCOO-]. The term is commonly used to refer to the ion itself. Bicarbonates are common constituents of drilling fluids. The ions are in equilibrium with carbonate and CO2 gas.

An integral bit and eccentric reamer used to simultaneously drill and underream the hole.

An agreement between two or more parties to review technical data prior to deciding whether to bid on a concession. The agreement also specifies the interests and the procedure for bidding between the parties in the event that the parties decide to bid on the concession.

A perforating charge designed to create perforations with a large-diameter entrance hole. These charges typically are used in sand control completions, in which efficient placement of the gravel pack treatment within the perforation tunnel is crucial. Altering the explosive charge design and materials creates a larger diameter entrance hole on the perforation while reducing the depth of penetration. However, gravel-pack treatments generally are applied in high-permeability formations where perforation tunnel length is less important. Wells that are to be hydraulically fractured also can benefit from larger perforations since the effective penetration is significantly increased by a high-conductivityfracture.

A perforating charge designed to create perforations with a large-diameter entrance hole. These charges typically are used in sand control completions, in which efficient placement of the gravel pack treatment within the perforation tunnel is crucial. Altering the explosive charge design and materials creates a larger diameter entrance hole on the perforation while reducing the depth of penetration. However, gravel-pack treatments generally are applied in high-permeability formations where perforation tunnel length is less important. Wells that are to be hydraulically fractured also can benefit from larger perforations since the effective penetration is significantly increased by a high-conductivityfracture.

A flow regime resulting from combined simultaneous linear flow in perpendicular directions. This flow regime is seen most commonly in tests of hydraulically fractured wells and occurs for finite-conductivity fracture where linear flow exists both in the fracture and to the fracture plane. This flow regime is recognized as a 1/4 slope in the pressure derivative on the log-log diagnostic plot. Its presence enables determination of the fracture conductivity.

A unit of measurement for large volumes of natural gas, abbreviated Bcf.

A common unit of measurement for large production rates of natural gas, abbreviated Bcf/D.

A type of corrosion in which two different metals are placed in contact in a corrosive environment. A small electric current flows from one piece of metal to the other, accelerating the corrosion rate of the more reactive of the two metals. Bimetallic corrosion is sometimes found when new pipe is added to old pipelines. The old pipeline covered by oxide and rust is cathodic to the new pipe, thus accelerating the corrosion rate in the new pipe. Another type of bimetallic corrosion is ringworm corrosion.

The electromagnetic force created by two different metals in contact with each other. If two such metals are in contact in a logging tool, and also communicate along a conductive borehole, then a potential drop is generated in the borehole. This potential drop will appear on the spontaneous potential (SP) log, where it can be confused with the electrochemical potential. Since the magnitude of the drop depends on the formationresistivity, the effect of bimetallism is often seen as a resistivity log superimposed on the normal SP. Under usual circumstances, the effect of bimetallism on the SP is small, and care is taken to avoid it.

To sort seismic data into small areas according to the midpoint between the source and the receiver, reflection point or conversion point prior to stacking.

The concentration of a particular substance in a living organism, possibly with harmful effects. The likelihood of this occurring is expressed as the bioaccumulation potential and can be estimated by the octanol/water partition coefficient, expressed as logPOW. This test is commonly required on drilling fluid additives in the North Sea area and other countries following the Oslo and Paris Commission (OSPAR) regulations. Values of logPOW below 3 indicate no bioaccumulation tendency; values between 3 and 6 indicate that bioaccumulation is possible, providing the substance is small enough to pass through the cell wall (mol. wt. < 600). This may be confirmed by a bioconcentration test in which a population of animals is exposed to the product.

A laboratory test or other assessment utilizing a living organism, such as mysid shrimp, to determine the effect of a condition to which the organism is exposed. Such tests are performed under controlled environmental conditions and duration. Bioassay tests of drilling fluids are required by governmental agencies throughout the world prior to discharge of mud or cuttings. The organisms used in bioassays are those found in the area that would be most affected by contact with the proposed drilling fluid. The dosage of interest is typically the lethal concentration, known as LC50, that will kill 50% of the population of organisms in a given period of time. Chronic bioassay tests indicate sublethal effects, such as changes in growth or reproduction of the organism over a longer period of time.

The amount of oxygen consumed by biodegradation processes during a standardized test. The test usually involves degradation of organic matter in a discarded waste or an effluent.

The breakdown of medium-weight crude oil by microbial organisms into heavy and light components. When the light components, typically methane, escape to the surface, the heavy ends are left behind. Biodegradation gradually raises oil viscosity, reduces API gravity, increases asphaltene content and increases concentration of certain metals and sulfur.

A polymer produced by a strain of bacteria. The most common type, used in drilling and completion operations, is a polysaccharide biopolymer known as XC polymer.

The application of plant and animal fossils to date and correlatestrata in order to elucidate Earth history, combining the principles of paleontology and stratigraphy. In the petroleum industry, biostratigraphy often denotes the use of terrestrial (pollen and spores) and marine (diatoms, foraminifera, nannofossils) microfossils to determine the absolute or relative age and depositional environment of a particular formation, source rock or reservoir of interest.

Referring to the flow of two immiscible fluids, oil and water, oil and gas, or gas and water.

A device containing a magnetometer and possibly other instruments that can be towed by an aircraft during aeromagnetic surveying or in a marine seismic streamer to provide dynamic information about the streamer position.

The splitting of an incident wave into two waves of different velocities and orthogonal polarizations. Birefringence occurs in optical mineralogy (see petrography) when plane-polarized light passes through an anisotropicmineral and emerges as two rays traveling at different speeds, the difference between which is characteristic of a mineral. In seismology, incident S-waves can exhibit birefringence as they split into a quasi-shear and a pure-shear wave. Although birefringence was first described by Danish physician Erasmus Bartholin (1625 to 1698) in crystals in 1669, the phenomenon was not fully understood until French physicist Etienne-Louis Malus (1775 to 1812) described polarized light in 1808.

The tool used to crush or cut rock. Everything on a drilling rig directly or indirectly assists the bit in crushing or cutting the rock. The bit is on the bottom of the drillstring and must be changed when it becomes excessively dull or stops making progress. Most bits work by scraping or crushing the rock, or both, usually as part of a rotational motion. Some bits, known as hammer bits, pound the rock vertically in much the same fashion as a construction site air hammer.

A container, usually made of steel and fitted with a sturdy lock, to store drill bits, especially higher cost PDC and diamond bits. These bits are extremely costly but often small in size, so they are prone to theft.

A special tool used by the rig crew to prevent the drill bit from turning while the bit sub on top of it is tightened or loosened. Bits have noncylindrical shapes, so the conventional wrenches used by the rig crew to tighten cylindrical shapes like pipes do not fit the bits properly. In addition, some bits, such as PDC bits, have a wide range of unusual and asymmetric shapes or profiles. The bit breaker must match the bit profile or the bit may be ruined before ever being used.

The part of the bit that includes a hole or opening for drilling fluid to exit. The hole is usually small (around 0.25 in. in diameter) and the pressure of the fluid inside the bit is usually high, leading to a high exit velocity through the nozzles that creates a high-velocity jet below the nozzles. This high-velocity jet of fluid cleans both the bit teeth and the bottom of the hole. The sizes of the nozzles are usually measured in 1/32-in. increments (although some are recorded in millimeters), are always reported in "thirty-seconds" of size (i.e., fractional denominators are not reduced), and usually range from 6/32 to 32/32.

A historical record of how a bit performed in a particular wellbore. The bit record includes such data as the depth the bit was put into the well, the distance the bit drilled, the hours the bit was being used "on bottom" or "rotating", the mud type and weight, the nozzle sizes, the weight placed on the bit, the rotating speed and hydraulic flow information. The data are usually updated daily. When the bit is pulled at the end of its use, the condition of the bit and the reason it was pulled out of the hole are also recorded. Bit records are often shared among operators and bit companies and are one of many valuable sources of data from offset wells for well design engineers.

The resistivity measured at the drill bit by a measurements-while-drilling (MWD) tool. The bit resistivity measurement responds to resistivity changes as the bit penetrates the formation, or when the time after bit is zero. It is thus an early indication of formation change.The measurement is similar to a wireline electrode device except that toroids are used instead of electrodes. A transmitter toroid induces a low-frequency current in the drillstring, which flows out of the bit and returns farther up the string. The magnitude of the current depends on the resistivity near the bit, and is measured by another toroid. The vertical resolution and depth of investigation depend on the distances between the toroids and the bit, which, in turn, depend on the type of bottomhole assembly (BHA) used. The depth of investigation is sufficient that the effect of the borehole is normally small.The measurement is unfocused and usually not borehole-corrected. Since both bit and drillstring are in physical contact with the formation, it is possible to make the measurement in oil-base muds.

The process of pulling the drillstring out of the wellbore for the purpose of changing a worn or underperforming drill bit. Upon reaching the surface, the bit is usually inspected and graded on the basis of how worn the teeth are, whether it is still in gauge and whether its components are still intact. On drilling reports, this trip may be abbreviated as TFNB (trip for new bit).

The fraction of naturally occurring, inflammable organic matter that is extractable from rock using organic solvents. Many petroleum precursors are composed of bitumen, but most are formed from kerogen in the process of petroleum generation. Bitumen includes hydrocarbons such as asphalt and mineral wax. Typically solid or nearly so, brown or black, bitumen has a distinctive petroliferous odor. Laboratory dissolution with organic solvents allows determination of the amount of bitumen in samples, an assessment of source rock richness. Burial and heating of kerogen yield bitumen, then liquid hydrocarbons, and then hydrocarbon gas. Understanding organic content is especially important in shale reservoirs because the shale is both the source rock and the reservoir rock in the petroleum system.

Analysis of two data sets that determines whether or not the data are related and describes the best relationship between them. Crossplots are often used to visualize potential bivariate relationships. Regression methods frequently help determine the best equation to fit to the data and the goodness of the fit.

A coring fluid formulated with components that are not likely to alter the wettability in the pores of the rock sample and that has low dynamic filtration characteristics. These qualities help retain the core's native properties and can retain some (or all) of the reservoir's fluids [water, oil and gas (gas only if kept under pressure)]. Bland water-base fluid is formulated to make the filtrate resemble the connate water in the reservoir. Keeping ionic composition and especially the pH matched to the reservoir water is most important. Thus, strong alkaline agents and clay deflocculants are avoided when designing bland coring fluids. Bland oil-base fluids should contain no water phase, and the base oil should resemble the reservoir oil. (Reservoir crude is used in some cases.) Amine, amide, phosphonated and sulfonated emulsifiers and the powerful oil-wetting agents are also avoided. Fatty acid soaps are chosen to emulsify the trace of water that is likely to be encountered. Additives that minimize dynamic filtration rate must be chosen. Setting mud density and bit hydraulics to give equivalent circulating density close to the reservoir pressure helps avoid filtrate invasion into the core. Designing core bits to core as fast as possible also limits filtrate invasion ahead of the bit.

A short section of plain tubing used to separate or space-out specialized components in a completion assembly. Blank pipe is commonly used in sand control completions where intervals of screen are separated by short sections of blank pipe. The term is also used to describe unperforated sections of casing or liner.

A gas phase maintained above a liquid in a vessel to protect the liquid against air contamination, to reduce the hazard of detonation or to pressurize the liquid. The gas source is located outside the vessel.

A section of heavy walled tubing that is placed across any perforated interval through which the production tubing must pass, such as may be required in multiple zone completions. In addition to being heavier than normal completion components, the wall of a blast joint is often treated to resist the jetting action that may result in the proximity of the perforations.

To equalize or relieve pressure from a vessel or system. At the conclusion of high-pressure tests or treatments, the pressure within the treatment lines and associated systems must be bled off safely to enable subsequent phases of the operation to continue. The bleedoff process must be conducted with a high degree of control to avoid the effect of sudden depressurization, which may create shock forces and fluid-disposal hazards.

A section of manifold containing the valves and piping necessary to bleed off pressure from a vessel or system. Bleedoff lines may be exposed to widely fluctuating pressures. They must be adequately secured, and consideration must be given to safe handling or disposal of the resulting fluids.

A mixture of crude oils, blended in the pipeline to create a crude with specific physical properties. Because heavy and extra-heavy crudes or bitumens cannot flow from the field to the refinery in their original state and at normal surface temperatures, they are blended with lighter crude oils primarily to reduce viscosity, thereby enabling transportation to a refinery. A secondary objective may be to provide a blended crude oil that has significantly higher value than the raw heavy crude. The blend is usually constructed so that the value of the overall blended volume is greater than the summed value of the initial volumes of individual heavy and light crudes.

The equipment used to prepare the slurries and gels commonly used in stimulation treatments. The blender should be capable of providing a supply of adequately mixed ingredients at the desired treatment rate. Modern blenders are computer controlled, enabling the flow of chemicals and ingredients to be efficiently metered and requiring a relatively small residence volume to achieve good control over the blend quality and delivery rate.

A simple slickline tool used to dislodge or push tools or equipment down the wellbore. The blind box is generally of heavy construction and is hardened to reduce damage when jarring is required.

A thick, heavy steel component of a conventional ram blowout preventer. In a normal pipe ram, the two blocks of steel that meet in the center of the wellbore to seal the well have a hole (one-half of the hole on each piece) through which the pipe fits. The blind ram has no space for pipe and is instead blanked off in order to be able to close over a well that does not contain a drillstring. It may be loosely thought of as the sliding gate on a gate valve.

A shadow zone, or a zone through which waves do not pass, or cannot be recorded, or in which reflections do not occur.

A set of pulleys used to gain mechanical advantage in lifting or dragging heavy objects. There are two large blocks on a drilling rig, the crown block and the traveling block. Each has several sheaves that are rigged with steel drilling cable or line such that the traveling block may be raised (or lowered) by reeling in (or out) a spool of drilling line on the drawworks.

An obstruction in the pipeline, composed of asphaltenes, hydrates, waxes, scale and sand deposited on the internal wall of the pipeline forming a barrier to the normal flow of fluids. The conditions for blockage formation are mainly encountered in deepwater operations (low temperature and high pressure).

To vent gas from a well or production system. Wells that have been shut in for a period frequently develop a gas cap caused by gas percolating through the fluid column in the wellbore. It is often desirable to remove or vent the free gas before starting well intervention work.

An uncontrolled flow of reservoir fluids into the wellbore, and sometimes catastrophically to the surface. A blowout may consist of salt water, oil, gas or a mixture of these. Blowouts occur in all types of exploration and production operations, not just during drilling operations. If reservoir fluids flow into another formation and do not flow to the surface, the result is called an underground blowout. If the well experiencing a blowout has significant openhole intervals, it is possible that the well will bridge over (or seal itself with rock fragments from collapsing formations) downhole and intervention efforts will be averted.

A large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. By closing this valve (usually operated remotely via hydraulic actuators), the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to open the BOP and retain pressure control of the formation. BOPs come in a variety of styles, sizes and pressure ratings. Some can effectively close over an open wellbore, some are designed to seal around tubular components in the well (drillpipe, casing or tubing) and others are fitted with hardened steel shearing surfaces that can actually cut through drillpipe. Since BOPs are critically important to the safety of the crew, the rig and the wellbore itself, BOPs are inspected, tested and refurbished at regular intervals determined by a combination of risk assessment, local practice, well type and legal requirements. BOP tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems.

To vent gas from a well or production system. Wells that have been shut in for a period frequently develop a gas cap caused by gas percolating through the fluid column in the wellbore. It is often desirable to remove or vent the free gas before starting well intervention work.

A phenomenon in which free gas leaves with the liquid phase at the bottom of the separator. Blowdy can indicate a low liquid level or improper level control inside the separator.

Opening the valve on a drip to allow natural gas to blow or clear the pipe of all liquids.

An uncontrolled flow of reservoir fluids into the wellbore, and sometimes catastrophically to the surface. A blowout may consist of salt water, oil, gas or a mixture of these. Blowouts occur in all types of exploration and production operations, not just during drilling operations. If reservoir fluids flow into another formation and do not flow to the surface, the result is called an underground blowout. If the well experiencing a blowout has significant openhole intervals, it is possible that the well will bridge over (or seal itself with rock fragments from collapsing formations) downhole and intervention efforts will be averted.

A large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. By closing this valve (usually operated remotely via hydraulic actuators), the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to open the BOP and retain pressure control of the formation. BOPs come in a variety of styles, sizes and pressure ratings. Some can effectively close over an open wellbore, some are designed to seal around tubular components in the well (drillpipe, casing or tubing) and others are fitted with hardened steel shearing surfaces that can actually cut through drillpipe. Since BOPs are critically important to the safety of the crew, the rig and the wellbore itself, BOPs are inspected, tested and refurbished at regular intervals determined by a combination of risk assessment, local practice, well type and legal requirements. BOP tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems.

A wave that propagates through a medium rather than along an interface. P-waves and S-waves are examples of body waves.

Slang term for a type of pressure vessel.

(noun) A cement evaluation log, typically acquired using a cement bond log (CBL) tool, that measures the acoustic amplitude and transit time of sound travelling through casing, cement sheath, and formation to assess the quality of the cement bond between casing and the wellbore wall.

A monetary incentive given by the lessee (either an individual or company) to the lessor (mineral owner) for executing or ratifying an oil, gas and mineral lease.

A small metal tube containing secondary high explosive that is crimped onto the end of the detonating cord. This explosive component is designed to provide reliable detonation transfer between perforating guns or other explosive devices, and often serves as an auxiliary explosive charge to ensure detonation.

The wellbore itself, including the openhole or uncased portion of the well. Borehole may refer to the inside diameter of the wellbore wall, the rock face that bounds the drilled hole.

An upgoing and downgoing arrangement of transducers in a logging tool, largely to offset spurious changes in reading caused by variations in borehole size or sonde tilt. The technique is used for measurements that rely on the propagation of a wave, such as sonic, propagation resistivity and electromagnetic propagation measurement.Propagation logs rely on measuring the difference in properties of a wave at two receivers. The borehole influences this difference if the tool is tilted or if there is a cave opposite one of the receivers. The effect can be compensated for by using two transmitters that radiate sequentially in opposite directions. In ideal conditions, the effect of a tilt or a cave is exactly opposite for the two transmitters, so that an average gives the correct result. Borehole compensation is different from borehole correction.

The amount by which a log measurement must be adjusted in order to remove the contribution of the borehole. Although most log measurements are designed to pick up a minimum of signal from the borehole, some contribution usually remains. This contribution may be removed by software or by manual entry into correction charts. In resistivitylogging, the correction replaces the borehole with a resistivity equal to that of the formation. In nuclear logging, the correction adjusts the reading to that which would be found in a standard condition, such as an 8-in. [20-cm] borehole filled with fresh water.

Pertaining to the detection of the Earth's gravitational field within a wellbore. Subtle vertical variations of the Earth's gravity field may be detected over the length of a borehole. These depend on the variations in the formation density not only above and below the sensor, but also laterally away from the borehole. Thus, borehole gravity measurements may be used to detect the following phenomena:- overburdenpressure- lateral formation density changes arising from porosity changes away from the borehole (fracture fields, vugs)- lateral proximity to lithology changes, such as major faulting or salt intrusions- time-lapse density measurements to monitor fluid saturation changes during the life of a reservoir.In borehole gravity measurements, highly accurate formation density measurements, averaged over a large volume, may be made by comparing changes of gravity between measurement stations.

A logging instrument capable of making relative gravity measurements at stations along the borehole with a sensitivity and repeatability in the microGal range (about 1 part in 10-9 of the Earth's gravity field)The only commercial measurement device capable of this precision is the LaCoste & Romberg borehole gravimeter, although several research projects have been proposed to replace this classic technology.

Seismic data measured with receivers, sources or both in a well, such as a check-shot survey, vertical seismic profile (VSP), crosswell seismic data or single-well imaging. By directly measuring the acoustic velocity of each formation encountered in a well, the well logs and borehole seismic data can be correlated to surface seismic data more easily. Borehole seismic data, including both S- and P-waves, can be gathered in a cased or openhole. This term is commonly used to distinguish between borehole sonic data (with frequencies typically greater than 1000 Hz) and borehole seismic data (with frequencies typically less than 1000 Hz).

An ultrasonic logging device with a radially mounted rotating transducer that is used to scan the borehole wall. The transducer (in transmit mode) emits a high-frequency pulse that is reflected by the borehole wall back to the transducer (in receive mode). In openhole applications, it can be used to measure the borehole diameter (by measuring the acoustictransit time between transducer and borehole wall) and the amplitude of acoustic signals reflected by the borehole wall. The transducer is rotated to produce a cross section of the borehole size and images of the borehole wall. These are used to identify fractures, breakouts and other borehole features. In cased hole, they are used to identify internal corrosion.

A procedure in which different chemicals are added to bottle samples of an emulsion to determine which chemical is the most effective at breaking, or separating, the emulsion into oil and water. Once an effective chemical is determined, varying amounts of it are added to bottle samples of the emulsion to determine the minimum amount required to break the emulsion effectively.

The bottom of the interval recorded on the log, or the deepest point at which the log readings are valid. At the bottom of the well, each log will have a valid first reading at a different depth. The bottom log interval is then either the lowermost first reading or the first reading of the most important log.

A specimen obtained from the bottom part of the tank or lower point in a pipeline.

The lower portion of the drillstring, consisting of (from the bottom up in a vertical well) the bit, bit sub, a mud motor (in certain cases), stabilizers, drill collar, heavy-weight drillpipe, jarring devices ("jars") and crossovers for various threadforms. The bottomhole assembly must provide force for the bit to break the rock (weight on bit), survive a hostile mechanical environment and provide the driller with directional control of the well. Oftentimes the assembly includes a mud motor, directional drilling and measuring equipment, measurements-while-drilling tools, logging-while-drilling tools and other specialized devices. A simple BHA consisting of a bit, various crossovers, and drill collars may be relatively inexpensive (less than $100,000 US in 1999), while a complex one may cost ten or more times that amount.

A downhole device used to control fluid flow under downhole conditions. Downhole chokes are generally removable with slickline intervention and are located in a landing nipple in the tubing string.

The temperature at the bottom of a well while fluid is being circulated, abbreviated BHCT. This is the temperature used for most tests of cementslurry in a liquid state (such as thickening time and fluid loss). In most cases, the BHCT is lower than the bottomhole static temperature (BHST), but in some cases, such as in deep water or in the arctic, the BHCT may be higher than the BHST.

(noun) A downhole device installed below or as part of the artificial lift system that separates free gas from the produced liquid before it enters the pump intake, reducing gas interference and improving pump efficiency in wells with high gas-liquid ratios.

A device installed at the bottom of a well to increase the temperature of the fluid coming from the reservoir. Bottomhole heaters are used in low API gravity crude oils to reduce the fluid viscosity, thus reducing the high friction forces normally associated with these types of fluids

The downhole pressure at which a treatment fluid can be injected into a zone of interest. The bottomhole injection pressure is typically calculated by adding the hydrostatic pressure of the fluid column to the surface pump pressure measured during an injection test.

The downhole pressure, measured or calculated at a point of interest, generally the top of the perforated interval.

A tool or assembly used to retrieve samples of fluids or fill material from the wellbore. Used as a treatment design aid, the retrieved samples can be checked for compatibility with the selected treatment fluid to verify performance or identify any undesirable reactions.

A well shut in slightly above the producing formation by use of special downhole tools containing a valve that can be preprogrammed or controlled from the surface. This practice is commonly associated with drillstem tests. Technology exists to employ bottomhole shut-in in suitably equipped completed wells.

A well shut in slightly above the producing formation by use of special downhole tools containing a valve that can be preprogrammed or controlled from the surface. This practice is commonly associated with drillstem tests. Technology exists to employ bottomhole shut-in in suitably equipped completed wells.

The undisturbed temperature at the bottom of a well, abbreviated as BHST. After circulation and after the well is shut in, the temperature approaches the BHST after about 24 to 36 hours, depending on the well conditions. The BHST is the temperature used in most tests in which the cementslurry is required to set or is set.

The downhole temperature measured or calculated at a point of interest. The BHT, without reference to circulating or static conditions, is typically associated with producing conditions.

Pertaining to the mud and cuttings that are calculated or measured to come from the bottom of the hole since the start of circulation. Circulation may be initiated after a static period, such as a trip, or from a given depth while drilling. This latter type is particularly useful to mud loggers and others trying to discern the lithology being drilled, so mud loggers or mud engineers often retrieve what is referred to as a "bottoms-up sample" of the cuttings or the drilling fluid.

A sample of mud from the deepest or current drilling depth of a well. The term refers particularly to a mud sample that has experienced stagnant conditions at the bottom of the hole, including the temperature, pressure and other conditions at that depth. A bottoms-up sample is commonly collected after a trip out of the hole or if an influx of formation fluid is suspected

Pertaining to the mud and cuttings that are calculated or measured to come from the bottom of the hole since the start of circulation. Circulation may be initiated after a static period, such as a trip, or from a given depth while drilling. This latter type is particularly useful to mud loggers and others trying to discern the lithology being drilled, so mud loggers or mud engineers often retrieve what is referred to as a "bottoms-up sample" of the cuttings or the drilling fluid.

A sample of mud from the deepest or current drilling depth of a well. The term refers particularly to a mud sample that has experienced stagnant conditions at the bottom of the hole, including the temperature, pressure and other conditions at that depth. A bottoms-up sample is commonly collected after a trip out of the hole or if an influx of formation fluid is suspected.

Fluid in the pore space that does not flow under normal reservoir conditions. This fluid may include water, oil or gas, but most often refers just to bound water. Bound fluid does not flow on primary or secondary production, injection or invasion unless the rock wettability is altered.When used in connection with a nuclear magnetic resonance measurement, the term refers to the signal that occurs below a certain cutoff, typically 33 ms in sandstones and 100 ms in carbonates. The source of this signal is bound water, but may also include oil with a viscosity above about 60 cp in sandstones or 30 cp in carbonates. Note that, contrary to the sense of "bound," this oil may or may not be moveable under normal reservoir conditions.

Water in the pore space that does not flow under normal reservoir conditions. Bound water does not flow on primary or secondary production, injection or invasion unless the rock wettability is altered.When used in connection with a nuclear magnetic resonance measurement, the term refers to all the water that is not free to move. This includes capillary-bound water and clay-bound water. However, water in mineral hydrates is not included as it relaxes too fast to be measured by nuclear magnetic resonance (NMR). In practice, bound water is defined as the water signal below a certain cutoff, typically 33 ms in sandstones and 100 ms in carbonates.When used in connection with the dual water model, the term refers to the clay-bound water only. In the Hill-Shirley-Klein model, the term is known as the hydration water.

A type of nuclear magnetic resonance (NMR) log that is designed to record properly only the bound fluid. Bound fluid is characterized by a fast relaxation time, typically less than 33 ms in sandstones and 100 ms in carbonate rocks. Therefore, the wait time for a bound fluid log can be much shorter than for standard NMR logs, with the result that logging speeds are much faster.

The flux (flow rate) or pressure states assigned to the theoretical boundaries used in developing and solving the differential equations that apply to well testing and in specifying a model to match to pressure-transient data.

Reservoirs with sealed or apparent outer boundaries that result in pressure depletion. Mathematical treatments differ between bounded and infinite reservoirs.

A concave-upward event in seismic data produced by a buried focus and corrected by proper migration of seismic data. The focusing of the seismic wave produces three reflection points on the event per surface location. The name was coined for the appearance of the event in unmigrated seismic data. Synclines, or sags, commonly generate bow ties.

A metal strip shaped like a hunting bow and attached to a tool or to the outside of casing. Bow-spring centralizers are used to keep casing in the center of a wellbore or casing ("centralized") prior to and during a cement job.

Relating to the female threadform, as in "box end of the pipe."

A grid pattern laid over a representation of fractures. The number of boxes that contain a fracture is counted and plotted against the box size on logarithmic scales. The slope of the line is equal to minus the fractal dimension. This is sometimes referred to as the box "dimension."

A type of multistrand wireline used for slickline applications in which higher tension or weight-carrying ability is required. The most common size of braided line is 3/16-in. diameter, although special heavy applications use 1/4-in. and 5/16-in. sizes. When larger sizes are used, it may be necessary to kill the well due to the effect of wellheadpressure on the relatively large cross-sectional area of the line entering the wellbore.

To apply the brake to slow the motion of the drawworks, and hence the drilling line and the drillstring.

To establish circulation of drilling fluids after a period of static conditions. Circulation may resume after a short break, such as taking a survey or making a mousehole connection, or after a prolonged interruption, such as after a round trip. The operation is of more concern to drillers and well planners with longer static intervals, since immobile drilling fluid tends to become less fluid and more gelatinous or semisolid with time.

To unscrew drillstring components, which are coupled by various threadforms known as connections, including tool joints and other threaded connections.

The pressure at which the rockmatrix of an exposed formation fractures and allows fluid to be injected. The breakdown pressure is established before determining reservoir treatment parameters. Hydraulic fracturing operations are conducted above the breakdown pressure, while matrix stimulation treatments are performed with the treatment pressure safely below the breakdown pressure.

A chemical used to reduce the viscosity of specialized treatment fluids such as gels and foams. Breaking down the fluid viscosity may be desirable either as part of a treatment, such as allowing flow back of the spent treatment fluid, or following a treatment as part of the fluid-disposal process. Depending on the application, a breaker of predictable performance may be incorporated into the treatment fluid for downhole activation, or be added directly to the returned fluid for immediate effect at surface.

To unscrew drillstring components, which are coupled by various threadforms known as connections, including tool joints and other threaded connections.

A clutching mechanism that permits the driller to apply high torque to a connection using the power of the drawworks motor.

Large capacity self-locking wrenches used to grip drillstring components and apply torque. The breakout tongs are the active tongs during breakout operations. A similar set of tongs is tied off to a deadline anchor during breakout operations to provide backup to the connection, not unlike the way a plumber uses two pipe wrenches in an opposing manner to tighten or loosen water pipes, except that breakout tongs are much larger.

A description of reservoir conditions under which a fluid, previously isolated or separated from production, gains access to a producing wellbore. The term is most commonly applied to water or gas breakthrough, where the water or gas injected to maintain reservoir pressure via injection wells breaks through to one or more of the producing wells.

A wellbore obstruction caused by a buildup of material such as scale, wellbore fill or cuttings that can restrict wellbore access or, in severe cases, eventually close the wellbore.

The accumulation or buildup of material, such as sand, fill or scale, within a wellbore, to the extent that the flow of fluids or passage of tools or downhole equipment is severely obstructed. In extreme cases, the wellbore can become completely plugged or bridged-off, requiring some remedial action before normalcirculation or production can be resumed.

A downhole tool that is located and set to isolate the lower part of the wellbore. Bridge plugs may be permanent or retrievable, enabling the lower wellbore to be permanently sealed from production or temporarily isolated from a treatment conducted on an upper zone.

The accumulation or buildup of material, such as sand, fill or scale, within a wellbore, to the extent that the flow of fluids or passage of tools or downhole equipment is severely obstructed. In extreme cases, the wellbore can become completely plugged or bridged-off, requiring some remedial action before normal circulation or production can be resumed.

Material of a coarse, fibrous or flaky composition used to form an impermeable barrier across a formation interface or perforation. Bridging materials are most commonly used when lost circulation occurs during drilling. They are also used in workover operations in preparation for killing a well when the kill fluid is likely to be lost to the perforations. The selection of an appropriate bridging material is critical during workover operations since the barrier should be completely removed in preparation for placing the well back on production.

A special section of cable that is placed between the logging cable and the head of the logging tool. Unlike the logging cable, the steel load-bearing element is in the center, surrounded by the conductors that are held in an insulating jacket. The bridle is needed for most conventional electrical logs and laterologs in which the cable armor is used as a current return. To be effective, this return must be at some distance from the logging tool and insulated from it. Typical bridles are 80 ft [24 m] long. Electrodes may be wound on the outside of the bridle and connected to the logging tool for use as measurement references or for spontaneous potential measurements.

A seismicamplitude anomaly or high amplitude that can indicate the presence of hydrocarbons. Bright spots result from large changes in acoustic impedance and tuning effect, such as when a gas sand underlies a shale, but can also be caused by phenomena other than the presence of hydrocarbons, such as a change in lithology. The term is often used synonymously with hydrocarbon indicator.

Water containing salts in solution, such as sodium, calcium or bromides. Brine is commonly produced along with oil. The disposal of oilfield brine is usually accomplished by underground injection into salt-water saturated formations or by evaporation in surface pits.

To prepare a well for production by initiating flow from the reservoir. This is the final phase of a completion or workover process.

A downhole tool used to repair the internal diameter of the production tubing where a slight collapse or a dent has occurred. Cutting profiles on a broach removes the tubing-wall material to allow subsequent passage of tools and equipment of a prescribed diameter.

A particular arrangement of transmitters and receivers used in the electromagnetic propagation measurement in which the dipoles used as sensors are oriented perpendicular to the axis of the tool. The orientation is combined with relatively short spacings to give a significant signal even in the most attenuative environments, such as salty muds.

An aqueous solution of sodium, calcium or zinc bromide salt or mixtures of these salts. These dense aqueous solutions are used for well completion and workover purposes.

An indicator used in place of methyl orange in alkalinity tests. It is green at pH values over 4.3, but yellow when pH is less than 4.3.

An oil or gas accumulation that has matured to a production plateau or even progressed to a stage of declining production. Operating companies seek to extend the economic producing life of the field using cost-effective, low-risk technologies. Stimulation or refracturing operations, completing additional zones, and installing artificial lift equipment are a few technologies commonly applied in brownfields before any drilling options are attempted.

A processed seismic record that contains traces from a common midpoint that have been added together but has undergone only cursory velocity analysis, so the normal-moveout correction is a first attempt. Typically, no static corrections are made before the brute stack.

The frequency with which a local probe detects a change from one type of fluid to another. For example, if water is the continuous phase, the probe will respond digitally each time a bubble of oil or gas passes it. The average frequency of change is the bubble count rate, or bubble count. In this example, an increasing bubble count means an increasing oil or gas velocity. Bubble velocity can be calculated from bubble count and bubble size, the latter being estimated from an empiricalcorrelation with water holdup. The depth at which the first bubbles are counted is a sensitive indicator of the lowest hydrocarbon entry.Since the bubble count is based on local probe measurements, both bubble count and bubble velocity can be presented as images, similar to the holdup image.

Bubble pulses or bubble noise that affect data quality. In marine seismic acquisition, the gas bubble produced by an air gun oscillates and generates subsequent pulses that cause source-generated noise. Careful use of multiple air guns can cause destructive interference of bubble pulses and alleviate the bubble effect. A cage, or a steel enclosure surrounding a seismic source, can be used to dissipate energy and reduce the bubble effect.

A multiphase flow regime in pipes in which one fluid moves as small dispersed bubbles through a continuous fluid. The relative velocity of the bubbles depends mainly on the difference in density between the two fluids. Bubble flow normally occurs at low flow rate and low holdup of the bubbly fluid. As the velocity of the continuous fluid increases, the bubbles are dispersed into smaller, more widely separated bubbles. This is known as a dispersed or finely dispersed bubble flow, or sometimes dispersed flow.

The pressure and temperature conditions at which the first bubble of gas comes out of solution in oil. At discovery, all petroleumreservoir oils contain some natural gas in solution. Often the oil is saturated with gas when discovered, meaning that the oil is holding all the gas it can at the reservoir temperature and pressure, and that it is at its bubblepoint. Occasionally, the oil will be undersaturated. In this case, as the pressure is lowered, the pressure at which the first gas begins to evolve from the oil is defined as the bubblepoint.

The pressure and temperature conditions at which the first bubble of gas comes out of solution in oil. At discovery, all petroleumreservoir oils contain some natural gas in solution. Often the oil is saturated with gas when discovered, meaning that the oil is holding all the gas it can at the reservoir temperature and pressure, and that it is at its bubblepoint. Occasionally, the oil will be undersaturated. In this case, as the pressure is lowered, the pressure at which the first gas begins to evolve from the oil is defined as the bubblepoint.

A coil in an inductionlogging tool designed to buck out, or reduce, the direct coupling between transmitter and receiver coils. The direct coupling signal is far larger than the formation signal. The bucking coil is wound with the opposite polarity to the main receiver coil, and placed in series with it at a location that minimizes the direct coupling. The combination of transmitter, main receiver and bucking coils is known as a mutually balanced array.

On a laterolog device, the current sent through a guard electrode (A1) with the purpose of focusing the current sent by the central current emitting electrode (A0). The bucking current maintains A1 and A0 at the same potential, thereby forcing the current from A0 to run approximately perpendicular to the sonde into the formation.

A chemical used to adjust and control the pH of stimulation fluids. Gels and complex polymer fluids are sensitive to pH changes, especially during the mixing phase when the dispersion and hydration of some polymers require specific pH conditions. In addition, the performance of crosslinked fluids is optimized over a relatively narrow pH range. Buffers, added to the aqueous phase before mixing, adjust the base-fluid pH to achieve a stable treatment fluid with the desired characteristics and predictable performance.

Any aqueous solution that contains a buffer mixture (weak acid or weak base and salt of the weak acid or base) to maintain constant or almost constant pH of the system.

A type of mud that contains the three components that form a chemical buffer, whether by design or by coincidence. Buffering results from components that react with the added OH- ions (or added H+ ions) forming slightly soluble or slightly ionized compounds. Water is one component of a buffer and various ions are the other components, such as bicarbonates, carbonates, lignite, lignosulfonate, silicate and sulfide. Clay solids are buffers because of their ability to accept or donate H+ ions on their surface. The pH of a buffered mud will not increase as fast as expected after addition of caustic soda, for example.

A solution used in analyses to hold pH at or above or below a certain value, as in the titration for magnesium versus calcium ions.

A vibrator truck equipped with wide tires to allow access to rugged or soggy terrain while causing less damage to the environment.

The measurement and analysis of (usually) bottomhole pressure data acquired after a producing well is shut in. Buildup tests are the preferred means to determine well flow capacity, permeability thickness, skin effect and other information. Soon after a well is shut in, the fluid in the wellbore usually reaches a somewhat quiescent state in which bottomhole pressure rises smoothly and is easily measured. This allows interpretable test results.

The ratio of stress to strain, abbreviated as k. The bulk modulus is an elastic constant equal to the applied stress divided by the ratio of the change in volume to the original volume of a body.

In a nuclear magnetic resonance measurement, the loss of coherent energy by hydrogen atoms as they interact with each other in bulk fluids. Bulk relaxation in fluids is caused primarily by fluctuating local magnetic fields arising from the random tumbling motion of neighboring molecules. Local field fluctuations may be high, but the fast movement of molecules tends to average these out. Thus the bulk relaxation depends strongly on the rate of movement and is affected by temperature and viscosity.In water-wet rocks, hydrocarbons do not touch the pore walls and are not affected by surface relaxation. Thus the T1 and T2 of hydrocarbons are the result only of bulk and diffusion relaxation. This is an important feature of NMR logging. Based on this feature, direct hydrocarbon-typing techniques have been developed for the detection and characterization of hydrocarbons.

The volume per unit mass of a dry material plus the volume of the air between its particles.

A solid plug used as an isolation device in piping systems, conduits or wellbore tubulars.

An early perforating method that used a hardened steel bullet or projectile, propelled by an explosive charge, to create a perforation tunnel. This method creates a low-permeabilitycrushed zone and leaves the bullet and associated debris jammed at the end of the tunnel. Jet perforating is now the preferred method.

To forcibly pump fluids into a formation, usually formation fluids that have entered the wellbore during a well control event. Though bullheading is intrinsically risky, it is performed if the formation fluids are suspected to contain hydrogen sulfide gas to prevent the toxic gas from reaching the surface. Bullheading is also performed if normal circulation cannot occur, such as after a borehole collapse. The primary risk in bullheading is that the drilling crew has no control over where the fluid goes and the fluid being pumped downhole usually enters the weakest formation. In addition, if only shallow casing is cemented in the well, the bullheading operation can cause wellbore fluids to broach around the casing shoe and reach the surface. This broaching to the surface has the effect of fluidizing and destabilizing the soil (or the subsea floor), and can lead to the formation of a crater and loss of equipment and life.

To observe the increase in pump pressure indicating that the top cement plug has been placed on the bottom plug or landing collar. Bumping the plug concludes the cementing operation.

Several pipes (production or injection, gas lift) that are jointly insulated to keep together production lines. The bundle minimizes heat transfer and avoids hydrate or wax deposition that could plug the pipelines. Bundles are common in deepwater field developments.

The upward force acting on an object placed in a fluid. The buoyancy force is equal to the weight of fluid displaced by the object. Buoyancy can have significant effects over a wide range of completion and workover activities, especially in cases in which the wellbore and tubing string contain liquid and gas. Any change in the relative volumes or fluid levels will change the buoyancy forces.

A technique for measuring the bulk volume of a core sample by submerging it in a bath of mercury and observing the increase in weight of the bath, following Archimedes principle. The bulk volume is calculated from the increase in weight divided by the density of mercury at the temperature of the bath. The sample must not touch the side of the bath and be only a few millimeters below the surface. Mercury is used because it is so strongly nonwetting and therefore does not enter the pore space.Other, less toxic, liquids may be used in the bath, such as brine, refined oil or toluene. In this case, the sample must be fully saturated with the liquid before immersion. In an alternative method, the saturated sample is weighed in air and then again once immersed. The bulk volume is then the difference in weight divided by the density of the liquid used.

The use of a mill or burn shoe to remove the outside area of a permanent downhole tool or fish. Burning over the obstruction provides a profile on which fishing or retrieval tools can be engaged to pull the obstruction from the wellbore.

The use of a mill or burn shoe to remove the outside area of a permanent downhole tool or fish. Burning over the obstruction provides a profile on which fishing or retrieval tools can be engaged to pull the obstruction from the wellbore.

A welding technique used to join two tubes in which the squared and prepared ends are butted together in preparation for welding. The resulting circumferential weld has relatively good strength characteristics but has limitations where the tube is to be plastically deformed or bent, such as occurs on a coiled tubing string. Consequently, butt welds performed on a coiled tubing string should be checked carefully using hardness and radiographic testing methods and their locations detailed in the string record. The anticipated fatigue life in the butt-weld area must also be reduced to compensate for the weakness of the weld.

A plot representing the effect of invasion on resistivity measurements that have different depths of investigation. The plot assumes a step profilemodel of invasion and determines true resistivity, flushed zone resistivity and diameter of invasion from ratios of deep-, medium- and shallow-resistivity measurements. Strictly speaking, when both resistive and conductive invasion are plotted, the chart is called a butterfly chart. When only one is plotted it is known as a tornado chart.

The resistivity measured by the buttons of a measurements-while-drilling (MWD) toroid device. Typically three buttons, each with a different depth of investigation, are mounted on a sleeve attached to the drillstring, and by their nature are azimuthally focused. The measurement is similar to a wirelinemicroresistivity log, except that toroids are used instead of electrodes for transmitting and monitoring. The button resistivities are focused measurements with vertical resolutions and depths of investigation of a few inches. With three button measurements, it is possible to correct for the presence of invasion, assuming a step profile.

A thread profile used on casing or linertubulars. Buttress threads are square-cut and create a hydraulic seal through the interference fit of the mating threads.

Describing the amount (in percent) of a material added to cement when the material is added based on the total amount of a specific blend, often abbreviated as BWOB.

Describing the amount (in percent) of a material added to cement, and is often abbreviated as BWOC. BWOC is the method used to describe the amount of most additives in the dry form.

Describing the amount (in percent) of a material added to a cementslurry based on the weight of water used to mix the slurry. Commonly abbreviated as BWOW, this convention normally is used only for salt [NaCl].

The act of passing the mud around a piece of equipment, such as passing mud returns around the shale shaker screens or going around a hydrocyclone device. From a mud-engineering viewpoint, this can be a bad practice because it can allow drill solids to degrade and accumulate as fines to the degree that they might cause mud problems.

In a spinner flowmeter, the theoretical minimum fluid velocity required to initiate spinner rotation, assuming the spinner response is linear. In this sense, it is synonymous with threshold velocity. However, it is sometimes taken to mean the fluid velocity at which a significant amount of flow begins to leak past a basket flowmeter, sufficient to cause the response to be nonlinear.

Mud that is left somewhere in the wellbore when some other fluid is pumped into the well. This can occur when pumping an oil mud into a well to displace a water mud. The bypassed water mud becomes a contaminant in the oil mud when it gets mixed into the circulating system. Drilling mud may be bypassed behind a casing or a liner when pumping cement into the casing or wellbore annular region. This mud-contaminated cement might not set up and might not isolate zones satisfactorily.