Oil and Gas Terms Beginning with “T”

In a nuclear magnetic resonance measurement, the characteristic time for longitudinal relaxation. In rocks, longitudinal relaxation is the inverse sum of the surface relaxation and bulk relaxation. T1 is not normally measured in NMRlogging, but is an important parameter in deciding the polarization time and hence the logging speed. T1 is closely related to the transverse relaxation time, T2. The ratio T1/T2 in water-filled rocks is typically between 1.5 and 2.5. In light hydrocarbons and gas, the ratio increases up to 10 and more as the viscosity decreases.

In nuclear magnetic resonance (NMR) logging, the characteristic time for transverse relaxation. In rocks, there are three components of the transverse relaxation?surface, Ts; bulk, Tb; and diffusion relaxation, Td. T2 is the inverse sum of each component for each fluid, as follows: 1/T2 = 1/Ts + 1/Tb + 1/Td.Because of the reciprocal sum, the smallest of the three types of relaxations is the most important in determining the final T2 for each fluid. There is not one single value of T2 for a rock but a wide distribution of values lying anywhere between fractions of a millisecond and several seconds. The distribution of T2 values is the principal output of an NMR log.

A term describing the application of a cloud pointglycol or polyglycol as a shaleinhibitor. The purported mechanism is that the glycol clouds out at the higher downhole temperatures, coating onto the surface of clays and preventing hydration

Abbreviation for Trans-Alaska Pipeline System

Steps in seismicprocessing to compensate for attenuation, spherical divergence and other effects by adjusting the amplitude of the data. The goal of TAR is to get the data to a state where the reflector amplitudes relate directly to the change in rock properties giving rise to them.

The use of tubing, drillpipe or coiled tubing to convey perforating guns to the required depth. Initially, the technique was developed as a means for conveying the gun string on the production tubing, with the guns remaining in the well until they are removed during the first workover. The subsequent popularity of highly deviated and horizontal wells increased the requirement for tubing-conveyed perforating as the only means of gaining access to the perforating depth. The term is often abbreviated as TCP.

The planned end of the well, measured by the length of pipe required to reach the bottom.

A mode of the electromagnetic field that involves only one component of the electric field and the two components of the magnetic field perpendicular to it; e.g., the x-component of the electric field and y- and z-components of the magnetic field. The TE mode is useful in describing 2D models in which the electric field is perpendicular to the 2D plane of the model. For this case, Maxwell's equations can be reduced to a single scalar equation for the electric field component, which simplifies calculations tremendously. There is an analogous mode for the magnetic field called the TM mode. A general EM field in a region without sources can be expressed as a sum of TE and TM modes.

Abbreviaton for technical evaluation agreement.

A variation of the electromagnetic method in which electric and magnetic fields are induced by transient pulses of electric current in coils or antennas instead of by continuous (sinusoidal) current. In the last two decades,TEM surveys have become the most popular surface EM technique used in exploration for minerals and groundwater and for environmental mapping.

(noun) Abbreviation for Thermally Enhanced Oil Recovery. A category of enhanced oil recovery methods that use heat to reduce crude oil viscosity and improve flow characteristics within the reservoir. TEOR techniques include steam flooding, cyclic steam stimulation (huff and puff), steam-assisted gravity drainage (SAGD), and in-situ combustion.

An abbreviation on drilling reports or mud logs signifying trip for new bit.

Gas entrained in the drilling fluid during a pipe trip, which typically results in a significant increase in gas that is circulated to surface. This increase arises from a combination of two factors: lack of circulation when the mud pumps are turned off, and swabbing effects caused by pulling the drillstring to surface. These effects may be seen following a short trip into casing or a full trip to surface.

Abbreviation for toe to heel air injection.

A mode of the electromagnetic field that involves only one component of the magnetic field and the two components of the electric field perpendicular to it; e.g., the x-component of the magnetic field and y- and z-components of the electric field. The TM mode is useful in describing 2D models in which the magnetic field is perpendicular to the 2D plane of the model. For this case, Maxwell's equations can be reduced to a single scalar equation for the magnetic field component, which simplifies calculations tremendously.

The concentration of organic material in source rocks as represented by the weight percent of organic carbon. A value of approximately 0.5% total organic carbon by weight percent is considered the minimum for an effective source rock, although values of 2% are considered the minimum for shale gas reservoirs; values exceeding 10% exist, although some geoscientists assert that high total organic carbon values indicate the possibility of kerogen filling pore space rather than other forms of hydrocarbons. Total organic carbon is measured from 1-g samples of pulverized rock that are combusted and converted to CO or CO2. If a sample appears to contain sufficient total organic carbon to generate hydrocarbons, it may be subjected to pyrolysis.

The vertical distance from a point in the well (usually the current or final depth) to a point at the surface, usually the elevation of the rotary kelly bushing (RKB). This is one of two primary depth measurements used by the drillers, the other being measured depth. TVD is important in determining bottomhole pressures, which are caused in part by the hydrostatic head of fluid in the wellbore. For this calculation, measured depth is irrelevant and TVD must be used. For most other operations, the driller is interested in the length of the hole or how much pipe will fit into the hole. For those measurements, measured depth, not TVD, is used. While the drilling crew should be careful to designate which measurement they are referring to, if no designation is used, they are usually referring to measured depth. Note that measured depth, due to intentional or unintentional curves in the wellbore, is always longer than true vertical depth.

The elapsed time for a seismicwave to travel from its source to a given reflector and return to a receiver at the Earth's surface. Minimum two-way traveltime is that of a normal-incidence wave with zero offset

Referring to the description of different regimes for the simultaneous flow of gas and liquid in vertical pipes introduced by Y. Taitel and A. Dukler in 1980. The results are shown in the form a crossplot or map with the superficial gas velocity, vgs, on the x-axis and the superficial liquid velocity, vls, on the y-axis. Different maps are constructed for different pipe sizes and fluid properties. The Taitel-Dukler map defines the transition between different flow regimes more closely than other models. Taitel and Dukler also described flow transitions in horizontal pipes.Reference:Taitel Y, Barnea D and Dukler AE: Modelling Flow Pattern Transitions for Steady Upward Gas-Liquid Flow in Vertical Tubes, AIChE Journal 26, no. 6 (May 1980): 345-354.

In multiphase flow, large bubbles of the lighter phase that form by coalescence of small bubbles under certain conditions of fluid flow. The large bubbles occur during slug flow and plug flow. The term is named after G.I. Taylor.Reference:Davies RM and Taylor G: The Mechanics of Large Bubbles Rising Through Liquids and Through Liquids in Tubes, Proceedings of the Royal Society of London, Series A. 200 (February 22, 1950): 375-390.

A portable mast that can be erected as a unit, with the upper section nested inside the lower section and raised by wireline or hydraulic system.

On an offshore jackup drilling rig, the deck below the rotary table and rig floor where workers can access the BOP stack. This platform surrounds the base of the BOP stack and is suspended from the cantilever (where the rig floor is located) by adjustable cables. It is accessed from the main deck of the jackup barge by a semipermanent stairwell. The Texas deck is used primarily for installing the wellhead and nippling the BOP stack up and down.

A device similar to a power swivel used in place of the rotary table to turn the drill string.

A legal document recorded each shift that includes employees' time and records different drilling information required by the oil company and regulatory bodies.

An 800-mile [1287-km], 48-in. [122-cm] pipeline that transports more than 1 million barrels of oil from Deadhorse (near Prudhoe Bay) to Valdez, Alaska, USA. The Trans-Alaska Pipeline System was completed in 1977 and it is often abbreviated as TAPS.

An assembly of sheaves mounted in a framework that moves up and down by use of the drilling line reeved over the crown block sheaves.

Any kind of pipe used in oilfield operations including tubing, casing, drill pipe, drill collars, and heavy-weight drill pipe.

A winching machine that hoists or pulls when a cable winds around a revolving drum. Also called a winch.

To contact, or tag, a known reference point or obstruction in the wellbore with the tubing string, wireline or other intervention equipment.

The last page or pages on a log print, which may contain data about the well, the recording parameters and the calibration of the measurements.

A floating device used in marineseismic acquisition to identify the end of a streamer. Tail buoys allow the seismic acquisition crew to monitor the location and direction of streamers. They are commonly brightly colored, reflect radar signals, and are fitted with Global Positioning System (GPS) receivers.

The last cement system pumped during primary cementing. The tail cement covers the lower sections of the well, especially planned completion intervals, and is typically more dense than the lead slurry that precedes it.

A cutoff in time, offset or both that has the effect of eliminating some types of noise from seismic data. A tail mute can be used to exclude slow surface waves such as ground roll.

The tubulars and completion components run below a production packer. The tail pipe may be included in a completion design for several reasons. It can provide a facility for plugs and other temporary flow-control devices, improve downhole hydraulic characteristics, and provide a suspension point for downhole gauges and monitoring equipment.

A list containing details of tubulars that have been prepared for running, or that have been retrieved from the wellbore. Each tubing joint is numbered and the corresponding length and other pertinent details noted alongside.

(noun) A graphical method used in directional drilling to plot the wellbore trajectory by assuming a straight-line path between successive survey stations at the inclination and azimuth measured at the lower station. While simple, the tangential method can accumulate positional errors in wells with rapidly changing direction.

A metal or plastic vessel used to store or measure a liquid. The three types of tanks in an oil field are drilling, production and storage tanks.

A group of tanks that are connected to receive crude oilproduction from a well or a producing lease. A tankbattery is also called a battery.In the tank battery, the oil volume is measured and tested before pumping the oil into the pipeline system.

The settlings -- sediment, dirt, oil emulsified with water and free water -- that accumulate in the bottom of storage tanks. The tank bottoms are periodically cleaned up and settlings can be disposed of or treated by chemicals to recover additional hydrocarbons. Tank bottoms are also called tank settlings or tank sludge.

(noun) The process of determining the relationship between liquid level and contained volume in a storage tank through physical measurement (strapping), optical methods, or liquid calibration techniques. Tank calibration tables are essential for accurate custody transfer and inventory management of crude oil and petroleum products.

A structure constructed around an oil tank to contain the oil in case the tank collapses. The volume or space inside the tank dike should be greater than the volume of the tank. A tank dike is also called a fire wall.

A table that shows the tank capacity in barrels as a function of the liquid level inside the tank. A tank table is also called a tank capacity table or gauge table.

The capacity of all the tanks in a field

A ship designed to transport crude oil, liquefied petroleum gas (LPG), liquefied natural gas (LNG), synthetic natural gas (SNG) or refined products. Tankers with 100,000 deadweight tons of capacity or more are called supertankers (very large crude carriers or ultralarge crude carriers). A tanker is also called a tank ship.

The acids found in tannin. Quebracho contains tannic acid.

Chemical extracted from the bark of trees and used as clay deflocculant in water muds. Tannins are moderate molecular weight, anionic polymers with complex structures. Quebracho is a tannin.

A fishing tool used to engage on the internal diameter of a hollow fish, such as drillpipe or drill collar. By rotating the taper tap when it is in contact with the fish, a threaded profile is cut, enabling the taper tap to securely engage the fish before retrieval.

In a nuclear magnetic resonance measurement, the use of a gradual rather than a sharp cutoff to distinguish between bound water and free water. A sharp cutoff at, for example T2 = 33 ms in sandstones, is normally used to distinguish free water (all T2s above 33 ms) from bound water (all T2s below 33ms). In a water-filled rock, in the fast diffusion limit, T2 is directly related to pore size. The distinction between bound and free water is based on the assumption that all free water resides in large pores, and all bound water in small pores. However, in rocks with large pores, a significant volume of bound water exists on the surface of the grains around a large pore. Being part of a large pore, it gives a long T2 and will be incorrectly counted as free water. One solution is the tapered cutoff, in which the bound water is the sum of all the T2 below a minimum, for example 5 ms, and is then a progressively smaller fraction of the volume at T2s up to a maximum, for example 500 ms. All signal above 500 ms represents free water. The form of the taper is usually empirical, but is based on some model of pore shape, such as a bundle of tubes.See Kleinberg RL and Boyd A: 'Tapered Cutoffs for Magnetic Resonance Bound Water Volume' paper SPE 38737, presented at the SPE Annual Technical Conference and Exhibition, San Antonio, Texas, USA, October 5-8, 1997.

A tubing string or work string that is made up from tubulars of different outside diameters (OD). In production applications, this may be used to improve the flow and production characteristics of a well. In drilling applications, a tapered string may be used to enable a small hole section to be drilled without changing the entire string. In coiled tubing operations, tapered strings are configured with a constant OD but with varying wall thickness.

A sand body that contains heavy hydrocarbon residues such as tar or asphalt, or degraded oil that has lost its volatile components. Hydrocarbons can be liberated from tar sands by heating and other processes, but tar sands, such as the Athabasca tar sands of Canada, are not commonly commercial because of high costs of production.Among some workers in the field of heavy oil, this term is falling out of use, in favor of the term "oil sand."

An agreement between a host country and operator to allow the operator to evaluate geological, geophysical, engineering and transportation issues involving a concession. Also known as a TEA.

Location relative to the boundary of a tectonic plate, particularly a boundary along which plate tectonic activity is occurring or has occurred.

(noun) The large-scale deformation of the Earth's crust driven by plate tectonic forces, including folding, faulting, uplift, and subsidence. Tectonism creates the structural traps, migration pathways, and basin geometries that control the distribution and accumulation of hydrocarbons.

A system for converting the measurements recorded by a wireline or measurements-while-drilling (MWD) tool into a suitable form for transmission to the surface. In the case of wireline logging, the measurements are converted into electronic pulses or analog signals that are sent up the cable. In the case of MWD, they are usually converted into an amplitude or frequency-modulated pattern of mud pulses. Some MWD tools use wirelines run inside the drillpipe. Others use wireless telemetry, in which signals are sent as electromagnetic waves through the Earth. Wireless telemetry is also used downhole to send signals from one part of an MWD tool to another.

A device used to indicate the position or function of mechanical components that cannot be easily observed, such as to indicate the launch of a cementing plug or dart.

A low-frequency electrical current that occurs naturally over large areas at or near the surface of the Earth. Telluric currents are induced by changes in Earth's magnetic field which are usually caused by interactions between the solar wind and the ionosphere (part of the upper atmosphere).

An electromagnetic method in which naturally occurring, low-frequency electric currents (telluric currents), are measured at a base station and compared with values measured at other stations. The normalized measurements of telluric current provide information about the direction of current flow and the conductance (conductivity times thickness) of sediments in the surveyed area. Extremely low-frequency telluric currents (with periods of days or months) provide information about conductivity in the deep interior of the Earth.

A record of the temperature gradient in a well. The temperature log is interpreted by looking for anomalies, or departures, from the reference gradient. This reference might be the geothermal gradient, a log recorded before production started or a log recorded with the well shut-in. Most anomalies are related to the entry of fluids into the borehole or fluid exit into the formation. Since the temperature is affected by material outside the casing, a temperature log is sensitive to not only the borehole but also the formation and the casing-formation annulus.Temperature logs have many applications, with the most common being to identify zones producing or taking fluid, to evaluate a cement or hydraulic fracture treatment, and to locate lost circulation zones and casing leaks. Since temperature takes time to dissipate, a temperature log tends to reflect the behavior of a well over a longer time period than other measurements.

The characteristic of a drilling fluid or a mud product pertaining to its response to prolonged heating, usually in a controlled mud composition in a rolling- or static-aging test.

A temperature data set taken at various depths in the wellbore. Temperature surveys are used to determine the top of cement behind the casing, fluid contacts and water influx. It is also useful to check for valve and casing leaks after the well has been temporarily shut down.

The force per unit cross-sectional area required to pull a substance apart.

A type of packer that is set by applying tension to the running string. These packers are less common than compression-set packers due to the potential difficulties associated with retrieval. However, in applications where there is insufficient string weight to set a compression packer, a tension packer is a useful option.

A mathematical entity with components that change in a particular way in a transformation from one coordinate system to another. Tensor methods are used in "upscaling" reservoir parameters for use in reservoir simulation studies.

An oil and gas lease that expires after a specified period of time, regardless of whether oil, gas and/or other minerals are being produced.

A graphical representation of concentrations in a system with three components. Since the sum of the component percentages is unity, any composition can be uniquely mapped to a single point within a triangular space. In many cases, a mixture of fluids with more than three components is divided into three pseudocomponents, such as light, intermediate and heavy components of a hydrocarbon phase. These diagrams are used to illustrate the phase behavior of a fluid.

The positive gravity correction that accounts for the deviation of the topography from the horizontal slab of infinite extent assumed in the Bouguer correction. Local topographic features always decrease the gravity measurement because the attractive force of the topography above the station is away from the Earth, and the effect of topography below the station is negative because of the absence of attractive material.

Pertaining to sediments or depositional environments on land or above the level of high tide.

Traditionally, the third stage of hydrocarbonproduction, comprising recovery methods that follow waterflooding or pressure maintenance. The principal tertiary recovery techniques used are thermal methods, gas injection and chemical flooding. The term is sometimes used as a synonym for enhanced oil recovery (EOR), but because EOR methods today may be applied at any stage of reservoirdevelopment, the term tertiary recovery is less commonly used than in the past.

A vessel used to separate and meter relatively small quantities of oil and gas. Test separators can be two-phase or three-phase, or horizontal, vertical or spherical. They can also be permanent or portable.Test separators sometimes are equipped with different meters to determine oil, water and gas rates, which are important to diagnose well problems, evaluate production performance of individual wells and manage reserves properly.Test separators can also be called well testers or a well checkers.

Pertaining to analysis based on equations or formulae derived from a theoretical basis in science. The majority of equations used in reservoir characterization and reservoir engineering are empirical, but many have been derived from scientific theory.

A parameter used to characterize thermal neutron interactions in bulk material. Thermal diffusion length (Ld) is the characteristic distance between the point at which a neutron becomes thermal and the point of its final capture. It is related to the quantity of thermal absorbers in the formation, and therefore is an important factor in the thermal neutron porosity measurement. Thermal neutrons have about the same energy as the surrounding matter, typically less than 0.4 eV (0.025 eV at room temperature).

The rate of increase in temperature per unit depth in the Earth. Although the thermal gradient varies from place to place, it averages 25 to 30 oC/km [15 oF/1000 ft].

The degree of heating of a source rock in the process of transforming kerogen into hydrocarbon. Thermal maturity is commonly evaluated by measuring vitrinite reflectance or by pyrolysis.

An element, or mineral, that is particularly effective in absorbing thermal neutrons (neutrons with about the same energy as the surrounding matter, typically less than 0.4 eV). The elements gadolinium, boron, chlorine, hydrogen and iron are thermal absorbers (in decreasing order of effectiveness). The effect of chlorine is used in a pulsed neutron capture log to distinguish salty water from hydrocarbons. In a thermal neutron porosity measurement, the effect of hydrogen is important, while boron and iron affect the response in shales.

A measurement of the slowing down and capture of neutrons between a source and one or more thermal neutron detectors. The neutron source emits high-energy neutrons that are slowed mainly by elastic scattering to near thermal levels. Thermal neutrons have about the same energy as the surrounding matter, typically less than 0.4 eV. The slowing-down process is dominated by hydrogen. At thermal levels, the neutrons diffuse through the material until they undergo thermal capture. Capture is dominated by chlorine, hydrogen and other thermal neutron absorbers.Typical thermal neutron measurements use a chemical neutron source and two thermal neutron detectors. An accelerator source (neutron generator) is sometimes used. Some, mainly earlier, devices measure the gamma rays emitted by thermal capture, rather than thermal neutrons.

A general term for injection processes that introduce heat into a reservoir. Thermal recovery is used to produce viscous, thick oils with API gravities less than 20. These oils cannot flow unless they are heated and their viscosity is reduced enough to allow flow toward producing wells.During thermal recovery, crude oil undergoes physical and chemical changes because of the effects of the heat supplied. Physical properties such as viscosity, specific gravity and interfacial tension are altered. The chemical changes involve different reactions such as cracking, which is the destruction of carbon-carbon bonds to generate lower molecular weight compounds, and dehydrogenation, which is the rupture of carbon-hydrogen bonds.Thermal recovery is a major branch of enhanced oil recovery processes and can be subdivided in two types: hot fluid injection such as steam injection (steamflood or cyclic steam injection) and hot waterflooding and in-situ combustion processes.

The finite-difference or finite-element reservoir simulation that includes energy equations and calculations used to describe heat conduction, heat and fluid convection, and latent heat exchanges occurring in the reservoir rock and fluids during a thermal recovery process such as steamflooding, steam assisted gravity drainage, or in-situ combustion. Combustion thermal simulation also requires equations for modeling combustion reaction kinetics.

A term describing the application of a cloud point glycol or polyglycol as a shaleinhibitor. The purported mechanism is that the glycol clouds out at the higher downhole temperatures, coating onto the surface of clays and preventing hydration.

A measurement of the time during which a cementslurry remains in a fluid state and is capable of being pumped. Thickening time is assessed under simulated downhole conditions using a consistometer that plots the consistency of a slurry over time at the anticipated temperature and pressure conditions. The end of the thickening time is considered to be 50 or 70 Bc for most applications.

A device that can be lowered into a tank to obtain samples (liquid or sediments) at different depths. The samples are analyzed to determine the gravity and BS&W content of the fluid into the tank.

An opening in the top of the stock tank. The thiefhatch allows tank access for a thief or other level measuring devices.

A formation encountered during drilling into which circulating fluids can be lost.

Pertaining to the ability of a fluid, such as cement or drilling mud, to develop gel strength over time when not subject to shearing, and then to liquefy when agitated.

The characteristic of a fluid, such as a drilling mud, to form a gelled structure over time when not subject to shearing and then to liquefy when agitated. The viscosity of a thixotropic fluid changes with time under constant shear rate until reaching equilibrium. Most drilling muds exhibit thixotropy, which is necessary for fast drilling, efficient cuttings lifting and to support weighting material when mud flow stops. Gel strength measured at various time intervals indicates the relative thixotropy of a mud.Thixotropy is sometimes desirable to provide resistance to flowing, such as to avoid or reduce losses or flow into a weak formation.

An element with an atomic number of 90. The 232Th isotope is radioactive and decays with a half-life of 1.4 * 1010 years through a series of intermediate isotopes to a stable isotope of lead. The intermediate isotopes emit a wide range of gamma rays, the most prominent being that of thallium, 208Tl. It is assumed that formations are in secular equilibrium; that is, the relative proportions of parent and daughter isotopes remain constant, and the measured spectrum is directly related to the amount of 232Th. The concentration in the Earth's crust is about 12 parts per million, ppm, by weight.Thorium-bearing minerals are rare. Thorium is a trace element associated with clays and heavy minerals. It is very immobile so that quantity measured today probably was present at the time of deposition. A log of thorium is presented in parts per million. It is often a good measure of clay content.

A common measure for volume of gas. Standard conditions are normally set at 60oF and 14.7 psia, abbreviated Mscf/d.

A protective sleeve or cap generally made up on the threads of tubular goods during transport and storage. Thread protectors are available in metal, plastic, or a combination of both.

A pocket-size thread gauge used in field operations to correctly identify or confirm the thread type and size of tubular goods.

A particular style or type of threaded connection, especially as used for rotary shouldered connections. Threadforms come in a variety of sizes, pitches, tapers, threads per in., and individual thread profiles. Fortunately, each of these varieties has a published standard, either considered public and maintained by the American Petroleum Institute (API) or maintained by operating or service companies as proprietary information.

A type of multicomponent seismic data acquired in a land, marine, or borehole environment by using three orthogonally oriented geophones or accelerometers. 3C is particularly appropriate when the addition of a hydrophone (the basis for 4C seismic data) adds no value to the measurement, as for example, on land. This technique allows determination of both the type of wave and its direction of propagation.

A set of numerous closely-spaced seismic lines that provide a high spatially sampled measure of subsurface reflectivity. Typical receiver line spacing can range from 300 m [1000 ft] to over 600 m [2000 ft], and typical distances between shotpoints and receiver groups is 25 m [82 ft] (offshore and internationally) and 110 ft or 220 ft [34 to 67 m] (onshore USA, using values that are even factors of the 5280 feet in a mile). Bin sizes are commonly 25 m, 110 ft or 220 ft. The resultant data set can be "cut" in any direction but still display a well sampled seismic section. The original seismic lines are called in-lines. Lines displayed perpendicular to in-lines are called crosslines. In a properly migrated 3D seismic data set, events are placed in their proper vertical and horizontal positions, providing more accurate subsurface maps than can be constructed on the basis of more widely spaced 2D seismic lines, between which significant interpolation might be necessary. In particular, 3D seismic data provide detailed information about fault distribution and subsurface structures. Computer-based interpretation and display of 3D seismic data allow for more thorough analysis than 2D seismic data.

The acquisition of seismic data as closely spaced receiver and shot lines such that there typically are no significant gaps in the subsurface coverage. A 2D survey commonly contains numerous widely spaced lines acquired orthogonally to the strike of geological structures and a minimum of lines acquired parallel to geological structures to allow line-to-line correlation of the seismic data and interpretation and mapping of structures.

The simultaneous flow of oil, free gas and water into a wellbore. Stratified flow is the rule rather than the exception.

A vessel that separates the well fluids into gas and two types of liquids: oil and water. A three-phaseseparator can be horizontal, vertical or spherical. This type of separator is commonly called a free-water knockout separator because its main use is to remove any free water that can cause problems such as corrosion and formation of hydrates or tight emulsions, which are difficult to break.The liquids (oil, water) leave the vessel at the bottom through different valves, and the gas leaves the vessel at the top, passing through a mist extractor to remove the small liquid droplets in the gas.

In a spinner flowmeter, the theoretical minimum fluid velocity required to initiate spinner rotation, assuming the spinner response is linear. The actual fluid velocity required to start spinner rotation is slightly higher because of additional viscous and mechanical effects. The threshold velocity is determined by extrapolating the spinner response at higher fluid velocities, where it is known to be nearly linear, back to the value that exists when spinner rotation is zero.

Pertaining to treatments performed on subsea wells where the fluids and associated pump-down equipment, such as plugs or darts, are pumped through the flowline normally used for production fluids.

Pertaining to a range of products, services and techniques designed to be run through, or conducted within, the production tubing of an oil or gas well. The term implies an ability to operate within restricted-diameter tubulars and is often associated with live-well intervention since the tubing is in place.

A perforating gun assembly designed to run through the restricted clearance of production tubing, then operate effectively within the larger diameter of the casing or liner below. A range of small-diameter guns has been developed for this purpose, although small-diameter casing guns also may be used when larger production tubing sizes permit.

A type of reverse fault in which the fault plane has a very shallow dip, typically much less than 45o. The hanging wall fault block moves up the fault surface relative to the footwall. In cases of considerable lateral movement, the fault is described as an overthrust fault. Thrust faults can occur in areas of compression of the Earth's crust.

In logging while drilling, a mark associated with each measurement indicating when a sample was taken. It is usually presented as a short bar in the depth track. Widely spaced tick marks indicate a low sampling rate. In wireline logging, a tick mark indicates the cumulative volume of some quantity, such as hole volume or traveltime. The term is sometimes spelled tic mark.

To correlate data in order to formulate or verify an interpretation or to demonstrate the relationship between data sets. Long, regional-scale 2D seismic lines are commonly tied to 3D surveys that cover a limited area, and 3D surveys of different vintages are tied to each other. Well logs are tied into seismic data routinely to determine the relationship between lithologic boundaries in the logs and seismic reflections. Properly tying all available data, including seismic data, well logs, check-shot surveys, synthetic seismograms and vertical seismic profiles, can reduce or, if there are sufficient data, eliminate ambiguity in interpretations.

In a ternary diagram, a graphical representation of two fluids being mixed. The ends of the tie line indicate the compositional concentrations of the two mixed fluids. The composition of the mixture lies on the line, with its position dependent on the concentration ratio of the two end-point fluids.

A section of liner that is run from a liner hanger back to the wellhead after the initial liner and hanger system have been installed and cemented. A tie-back liner may be required to provide the necessary pressure capacity during a flow-test period or for special treatments, and is typically not cemented in place. In some cases, a tie-back liner will be installed as a remedial treatment when the integrity of the intermediate casing string is in doubt.

A specially designed packer assembly used in conjunction with a tie-back liner. The tie-back packer can be integral to the original liner hanger, or if the tie-back is a remedial treatment, it can be a separate component set above the liner hanger.

(noun) A section of casing or liner run from the top of a previously hung liner back up to the wellhead, creating a continuous casing string from surface to the liner setting depth. Tie-back strings are used to provide additional casing integrity, isolate problematic zones, or convert a liner completion to a full casing string.

Secrecy or confidentiality of information. Operators typically try to prevent disclosure of results from exploration wells and will hold any such information "tight". A tight hole is a well whose status and data are not widely disseminated by the operator.

An emulsion with small and closely distributed droplets. A tight emulsion can be difficult to break.

Gas produced from a relatively impermeablereservoirrock. Hydrocarbonproduction from tight reservoirs can be difficult without stimulation operations. Stimulation of tight formations can result in increased production from formations that previously might have been abandoned or been produced uneconomically. The term is generally used for reservoirs other than shales.

A well that the operator requires be kept as secret as possible, especially the geologic information. Exploration wells, especially rank wildcats, are often designated as tight. Unfortunately, this designation is of questionable benefit in keeping the data secret.

The time that has elapsed between the bit first penetrating a formation and a log being recorded opposite it. In logging while drilling, this time is different for each log, since it depends on the drilling rate and the distance between the bit and the particular logging sensor.

The use of a function of time rather than frequency to express an independent variable or measurement. In contrast, in the frequency domain, variables are expressed as a function of frequency instead of time.

A migration technique for processing seismic data in areas where lateral velocity changes are not too severe, but structures are complex. Time migration has the effect of moving dipping events on a surface seismic line from apparent locations to their true locations in time. The resulting image is shown in terms of traveltime rather than depth, and must then be converted to depth with an accurate velocity model to be compared to well logs.

A horizontal display or map view of 3D seismic data having a certain arrival time, as opposed to a horizon slice that shows a particular reflection. A time slice is a quick, convenient way to evaluate changes in amplitude of seismic data.

Pertaining to techniques in which the same quantity is measured at different times in the life of a reservoir. Normally the only change in a time-lapse measurement or survey will be due to changes in water or gas saturation. Thus, a comparison of two logs run at different times, such as a year apart, should simply reflect the change in fluid saturations in the pore space. The most common time-lapse logs are made with pulsed neutron capture, pulsed neutron spectroscopy and boreholegravity measurements.

Seismic data from the surface or a borehole acquired at different times over the same area to assess changes in the subsurface with time, such as fluid movement or effects of secondary recovery. The data are examined for changes in attributes related to expressions of fluid content. Time-lapse seismic data can repeat 2D, 3D (which is known as 4D seismic data), crosswell and VSP data.

A technique for determining the velocity of fluid flow in an injection well based on measuring the time a slug of radioactive tracer takes to move down the well. The analysis is usually performed as part of a tracer-loss measurement. The depth of the slug is measured by running repeated gamma ray logs at well-defined time intervals. From the differences in depth and time, the velocity can be determined.

In chemical analysis, a procedure to determine the amount of a constituent in a sample by adding a measured volume of reagent until the reaction between the constituent of interest and the reagent is completed, as shown by an appropriate endpoint indicator. For mud and mud filtrate analyses, titration is a common procedure for determining alkalinity, chloride, total hardness, methylene blue capacity and formaldehyde.

An in-situ combustion method for producing heavy oil. In this technique, the fireflooding starts from a vertical well, while the oil is produced from a horizontal well having its toe in close proximity to the vertical air-injection well. This production method is a modification of conventional fire flooding techniques in which the flame front from a vertical well pushes the oil to be produced from another vertical well.

A technique to measure and display the three-dimensional distribution of velocity or reflectivity of a volume of the Earth by using numerous sources and receivers. There are several types of tomography used by geophysicists, including transmission tomography (which uses measurements between boreholes, surface-to-surface, or between a borehole and the surface), reflection or seismic tomography (based on standard reflection seismology), and diffraction tomography (using Fermat's principle for computations instead of Snell's law). Variations in velocity can be attributed to changes in density and elastic properties of rocks, which in turn are affected by the increasing temperature with depth in the Earth. Tomographic techniques have been used to construct maps of the Earth's interior, deep in the mantle, as well as for mapping the shallow subsurface by borehole tomography.

Large-capacity, self-locking wrenches used to grip drillstring components and apply torque. As with opposing pipe wrenches for a plumber, the tongs must be used in opposing pairs. As a matter of efficiency, one set of tongs is essentially tied off with a cable or chain to the derrick, and the other is actively pulled with mechanical catheads. The breakout tongs are the active tongs during breakout (or loosening) operations. The makeup tongs are active during makeup (or tightening) operations.

The enlarged and threaded ends of joints of drillpipe. These components are fabricated separately from the pipe body and welded onto the pipe at a manufacturing facility. The tool joints provide high-strength, high-pressure threaded connections that are sufficiently robust to survive the rigors of drilling and numerous cycles of tightening and loosening at threads. Tool joints are usually made of steel that has been heat treated to a higher strength than the steel of the tube body. The large-diameter section of the tool joints provides a low stress area where pipe tongs are used to grip the pipe. Hence, relatively small cuts caused by the pipe tongs do not significantly impair the strength or life of the joint of drillpipe.

(noun) An assembly of multiple downhole tools connected end-to-end and run into the wellbore on wireline, coiled tubing, or drillpipe to perform a specific operation such as production logging, perforating, or fishing. The configuration and sequence of tools in the string are designed to accomplish the objectives of the intervention.

The location supervisor for the drilling contractor. The toolpusher is usually a senior, experienced individual who has worked his way up through the ranks of the drilling crew positions. His job is largely administrative, including ensuring that the rig has sufficient materials, spare parts and skilled personnel to continue efficient operations. The toolpusher also serves as a trusted advisor to many personnel on the rigsite, including the operator's representative, the company man.

An oil and gas lease wherein the bonus consideration is paid at the signing of the lease. However, this lease becomes effective only after the expiration or termination of an existing lease on the tract of land.

The top of the interval recorded on the log, or the shallowest point at which the log readings are valid. If the top of the log is at the casing shoe, the last valid reading of many logs will be a short distance below. However, it is common to give the depth of the casing shoe as the top log interval.

A device that turns the drillstring. It consists of one or more motors (electric or hydraulic) connected with appropriate gearing to a short section of pipe called a quill, that in turn may be screwed into a saver sub or the drillstring itself. The topdrive is suspended from the hook, so the rotary mechanism is free to travel up and down the derrick. This is radically different from the more conventional rotary table and kelly method of turning the drillstring because it enables drilling to be done with three joint stands instead of single joints of pipe. It also enables the driller to quickly engage the pumps or the rotary while tripping pipe, which cannot be done easily with the kelly system. While not a panacea, modern topdrives are a major improvement to drilling rig technology and are a large contributor to the ability to drill more difficult extended-reach wellbores. In addition, the topdrive enables drillers to minimize both frequency and cost per incident of stuck pipe.

A contour map that displays the elevation of the Earth's surface. A topographic map is commonly used as the base map for surface geological mapping.

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 invasion 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 connection between the wirelineloggingcable and the bridle. The torpedo consists of an outer mechanical connection enclosing electrical connections between the conductors.

A device for measuring in situ the velocity of fluid flow in a production or injection well based on the torque, or force, produced by the fluid on a stationary impeller. This torque can be related to the effective velocity of flow across the impeller. The torque flowmeter is sometimes used as an alternative to the spinner flowmeter.

The bottom of a particular hole section, where drilling is stopped, logs are run and casing is cemented before starting the next, smaller diameter hole section.

A chemical analysis to measure the hardness ions in water-mud filtrates or in make-up water. Hardness is quantitatively determined by titration using standardized EDTA (versenate) reagent and ammonium hydroxide (weak) buffer, typically according to procedures of API. Results are reported as calcium ion in mg/L. The hardness ion Ca+2 can be analyzed alone by another EDTA titration method described by the API.

The concentration of organic material in source rocks as represented by the weight percent of organic carbon. A value of approximately 0.5% total organic carbon by weight percent is considered the minimum for an effective source rock, although values of 2% are considered the minimum for shale gas reservoirs; values exceeding 10% exist, although some geoscientists assert that high total organic carbon values indicate the possibility of kerogen filling pore space rather than other forms of hydrocarbons. Total organic carbon is measured from 1-g samples of pulverized rock that are combusted and converted to CO or CO2. If a sample appears to contain sufficient total organic carbon to generate hydrocarbons, it may be subjected to pyrolysis.

The total pore volume per unit volume of rock. It is measured in volume/volume, percent or porosity units.The total porosity is the total void space and as such includes isolated pores and the space occupied by clay-bound water. It is the porosity measured by core analysis techniques that involve disaggregating the sample. It is also the porosity measured by many log measurements, including density, neutron porosity and nuclear magnetic resonance logs.

A work shift of a drilling crew. Drilling operations usually occur around the clock because of the cost to rent a rig. As a result, there are usually two separate crews working twelve-hour tours to keep the operation going. Some companies prefer three eight-hour tours. The graveyard tour is the overnight shift or the shift that begins at midnight. (Pronounced "tower" in many areas.)

The presentation on hard copy of log data from a single measurement versus depth. The term originated with the early optical recorders in which log data were recorded on film using an optical trace. Now the term curve is more common.

A technique in which a tracer is injected into the flow stream of a production or injection well to determine fluid paths and velocities. Radioactive tracers have been used from the 1940s and are still common for determining flow profiles in injection wells. Tracers with high neutron-capture cross section, such as borax or high-salinity water, were introduced in the 1970s to record injection/pulsed neutron logs. In multiphase production wells, special tracers were introduced in the 1990s to move with only one phase, so as to give a phase-velocity log. Radioactive tracers with different energies are used to track the development of fractures, or other processes, in the multiple-isotope log.Tracer measurements are used qualitatively to determine the movement of fluids behind pipe, or quantitatively to determine fluid-flow velocity within the pipe.

(noun) A production logging technique in which a radioactive or chemical tracer is ejected from a tool into the wellbore fluid stream and detected by sensors positioned above or below the ejection point to determine the velocity, direction, and distribution of fluid flow across producing or injecting intervals.

A method of determining injection-flow profiles by monitoring the reduction in tracer material as it moves down the well. A slug of radioactive tracer is added to the injection fluid. As the slug moves down the well, several gamma ray logs are recorded at well-defined time intervals. The position of the slug is seen as a large gamma ray peak whose size is proportional to the flow rate. A reduction in the size of the peak indicates a loss of fluid into the formation. Fluid velocity can be calculated from the time interval and the distance the peak has moved using timed-slug analysis. Tracer-loss measurements produce a type of radioactive-tracer log, used mainly to give a general idea of fluid flow in low flow-rate wells.In very low flow-rate wells, an alternative technique has been used in which the gamma ray detector is held stationary at some depth until the slug has passed. The detector is then moved down to another depth to observe the slug again. With these data, it is possible to make quantitative estimates of fluid flow.

A vertical section of a log presentation over which one particular set of data is displayed. The track divides the presentation into different sections, each with a certain set of log curves or other data, such as depth numbers. The section is vertical in the sense that it is along the depth or time axis of the log. The curves are usually blanked off when they run outside their allotted track. Tracks are typically numbered from left to right across the page (when viewed with depth or time increasing towards the bottom of the page).

A particular type of strike-slip fault that is a boundary of an oceanic tectonic plate. The actual movement of a transform fault is opposite to its apparent displacement because of the interplay of spreading and faulting between tectonic plates.

The migration of shoreline out of a basin and onto land during retrogradation. A transgression can result in sediments characteristic of shallow water being overlain by deeper water sediments.

A marine flooding surface separating the underlying lowstand systems tract from the overlying transgressivesystems tract. Typically, this is the first major flooding surface following the lowstand systems tract.

(noun) The radial distance from a wellbore to which a pressure disturbance has propagated during a well test before reaching a reservoir boundary or achieving pseudo-steady-state conditions. The transient drainage radius increases with time as the pressure pulse moves outward through the formation.

A variation of the electromagnetic method in which electric and magnetic fields are induced by transient pulses of electric current in coils or antennas instead of by continuous (sinusoidal) current. In the last two decades,TEM surveys have become the most popular surface EM technique used in exploration for minerals and groundwater and for environmental mapping.

The change in pressure with time. In well testing, this refers to the pressure measured as a function of time after the test is initiated.

The pressure response resulting from changes in a well's production rate. This includes drawdown, in which the pressure falls in response to the production of fluids; buildups, in which the pressure rises after a well is shut in; and falloffs, in which the pressure falls after an injection well is shut in.

The pressure measurements recorded as a function of time, usually in the wellbore near the productive interval, after the flow rate of the well is changed. These form the basis for transient well-test analysis, and are primarily used for determining reservoir-rock properties and producing-formation limits.

The analysis of transient rate and pressure data taken while a well is flowing at variable rates. The analysis uses either deconvolution or convolution to correct for the flow-rate variations and can make drawdown data interpretable. It has also been applied to correct for afterflow during the buildup.

The duration of time for a P-wave to travel one foot, typically displayed on an acoustic log. The unit of microseconds per foot (or meter) is called the slowness, which is the inverse of velocity.

A multiphase-fluid flow regime characterized by a chaotic mixture of liquid and gas, with neither phase appearing to be continuous. Also known as churn flow, transition flow is an intermediate flow condition between slug flow and mist flow.

With reference to invasion, the volume between the flushed zone and the undisturbed zone in which the mudfiltrate has only partially displaced the moveable formation fluids. One common model of invasion assumes a smooth transition in resistivity and other formation properties from the flushed to the undisturbed zone. Based on this assumption, the inner and outer diameters of invasion can be determined from array resistivity logs. Another common invasion model, which does not assume a smooth transition, is the annulus.

A technique used in crosswell seismic and electromagnetic tomography for recording the direct signal from the source or transmitter in one well to the receiverarray in another well. This technique is used for mapping the distribution of acoustic velocity and attenuation or electromagnetic resistivity between wells.

The simultaneous occurrence of strike-slip faulting and compression, or convergence, of the Earth's crust. In areas of transpression, rocks can be faulted upward to form a positive flower structure. Areas of strike-slip faulting in rifting or diverging crust are experiencing transtension, in which rocks can drop down to form a negative flower structure.

The simultaneous occurrence of strike-slip faulting and extension, rifting, or divergence of the Earth's crust. In areas of transtension, rocks can be faulted downward to form a negative flower structure. Areas of strike-slip faulting in converging crust are experiencing transpression, in which rocks can be faulted upwards to form a positive flower structure.

A mode of the electromagnetic field that involves only one component of the electric field and the two components of the magnetic field perpendicular to it; e.g., the x-component of the electric field and y- and z-components of the magnetic field. The TE mode is useful in describing 2D models in which the electric field is perpendicular to the 2D plane of the model. For this case, Maxwell's equations can be reduced to a single scalar equation for the electric field component, which simplifies calculations tremendously. There is an analogous mode for the magnetic field called the TM mode. A general EM field in a region without sources can be expressed as a sum of TE and TM modes.

A mode of the electromagnetic field that involves only one component of the magnetic field and the two components of the electric field perpendicular to it; e.g., the x-component of the magnetic field and y- and z-components of the electric field. The TM mode is useful in describing 2D models in which the magnetic field is perpendicular to the 2D plane of the model. For this case, Maxwell's equations can be reduced to a single scalar equation for the magnetic field component, which simplifies calculations tremendously.

The loss of coherent energy by protons in a rock while precessing about a static magnetic field during a nuclear magnetic resonance measurement. The loss of coherent energy, or relaxation, due to the free induction decay is corrected by the CPMG pulse sequence. This leaves three mechanisms for relaxation: surface relaxation, bulk relaxation and diffusion relaxation, all of which depend on formation properties. Transverse relaxation is characterized by an exponential decay of time constant T2.

A configuration of rocks suitable for containing hydrocarbons and sealed by a relatively impermeable formation through which hydrocarbons will not migrate. Traps are described as structural traps (in deformed strata such as folds and faults) or stratigraphic traps (in areas where rock types change, such as unconformities, pinch-outs and reefs). A trap is an essential component of a petroleum system.

Oil in pore spaces that cannot be moved because of capillary forces. Typical trapped or residual oilsaturation is in the range of 10% to 50% of the pore space, and it is higher in tighter formations where the pore spaces are small. The amount of trapped oil is a function of the displacement method and conditions, making this oil a target for enhanced oil recovery (EOR) processes. EOR methods introduce fluids that reduce viscosity, interfacial tension or mobility ratio, and thus improve flow and sweep efficiency to release the residual oil.

(noun) A section of tubing with a polished bore receptacle or seal assembly that permits relative axial movement between the tubing string and a downhole packer, accommodating thermal expansion, contraction, and pressure-induced length changes in the completion string during production or injection operations.

The set of sheaves that move up and down in the derrick. The wire rope threaded through them is threaded (or "reeved") back to the stationary crown blocks located on the top of the derrick. This pulley system gives great mechanical advantage to the action of the wire rope drilling line, enabling heavy loads (drillstring, casing and liners) to be lifted out of or lowered into the wellbore.

In a subsurface sucker-rod pump, the valve that closes the barrel chamber allowing the trapped fluid to be lifted in the upstroke of the pump. This valve is similar in configuration to the standing valve.

The slip set on a snubbing unit that is located at the top of the jack assembly. Two sets of travelling slips are available, one set for heavy-pipe conditions and another for light-pipe conditions.

The travelling slip set on a snubbing unit that is used when operating under light-pipe conditions. Under these conditions, the wellheadpressure is sufficient to eject the tubing string from the wellbore. Therefore, the slips are oriented in a hold-down position to act against the upward force applied to the tubing string.

The duration of the passage of a signal from the source through the Earth and back to the receiver. A time seismic section typically shows the two-way traveltime of the wave.

A vessel used to treat oil-water emulsions so the oil can be accepted by the pipeline or transport. A treater can use several mechanisms. These include heat, gravity segregation, chemical additives and electric current to break emulsions.There are vertical and horizontal treaters. The main difference between them is the residence time, which is shorter in the vertical configuration compared with the horizontal one.A treater can be called a heater treater or an emulsion treater.

The temporary surface piping, valves and manifolds necessary to deliver a fluid treatment to the wellbore from the mixing and pumping equipment.

A fluid designed and prepared to resolve a specific wellbore or reservoir condition. Treatment fluids are typically prepared at the wellsite for a wide range of purposes, such as stimulation, isolation or control of reservoir gas or water. Every treatment fluid is intended for specific conditions and should be prepared and used as directed to ensure reliable and predictable performance.

Used synonymously with the term play to describe an area in which hydrocarbons occur, such as the Wilcox trend of the Gulf Coast.

Gas entrained in the drilling fluid during a pipe trip, which typically results in a significant increase in gas that is circulated to surface. This increase arises from a combination of two factors: lack of circulation when the mud pumps are turned off, and swabbing effects caused by pulling the drillstring to surface. These effects may be seen following a short trip into casing or a full trip to surface.

A positive-displacementreciprocating pump that is configured with three plungers. Triplex pumps are the most common configuration of pump used in both drilling and well service operations. Pumps used in well service activities generally are capable of handling a wide range of fluid types, including corrosive fluids, abrasive fluids and slurries containing relatively large particulates.

The act of pulling the drillstring out of the hole or replacing it in the hole. A pipe trip is usually done because the bit has dulled or has otherwise ceased to drill efficiently and must be replaced.

The minimum (negative) deflection of the seismic wavelet. Seismic interpreters commonly pick or track seismic data on paper sections along the trough of a wavelet rather than the solid-colored peak. With the advent of workstations, this is no longer necessary because of automatic picking techniques and the ability to reverse the polarity of the data in real time.

With reference to core analysis, the resistivity of a sample only partially filled with water. Called Rt, it is used in contrast to the resistivity of a sample completely filled with water, Ro. The water may be replaced by any nonconductive fluid, usually air or dead oil.

The thickness of a bed or rock body after correcting for the dip of the bed or body and the deviation of the well that penetrates it. The values of true stratigraphic thickness in an area can be plotted and contours drawn to create an isopach map.

The vertical distance from a point in the well (usually the current or final depth) to a point at the surface, usually the elevation of the rotary kelly bushing (RKB). This is one of two primary depth measurements used by the drillers, the other being measured depth. TVD is important in determining bottomhole pressures, which are caused in part by the hydrostatic head of fluid in the wellbore. For this calculation, measured depth is irrelevant and TVD must be used. For most other operations, the driller is interested in the length of the hole or how much pipe will fit into the hole. For those measurements, measured depth, not TVD, is used. While the drilling crew should be careful to designate which measurement they are referring to, if no designation is used, they are usually referring to measured depth. Note that measured depth, due to intentional or unintentional curves in the wellbore, is always longer than true vertical depth.

The thickness of a bed or rock body measured vertically at a point. The values of true vertical thickness in an area can be plotted and contours drawn to create an isochore map.

Steps in seismic processing to compensate for attenuation, spherical divergence and other effects by adjusting the amplitude of the data. The goal of TAR is to get the data to a state where the reflector amplitudes relate directly to the change in rock properties giving rise to them.

An interface wave that occurs in cased wellbores when a Rayleigh wave encounters a wellbore and perturbs the fluid in the wellbore. The tube wave travels down the wellbore along the interface between the fluid in the wellbore and the wall of the wellbore. A tube wave suffers little energy loss and typically retains a very high amplitude which interferes with reflected arrivals occurring later in time on vertical seismic profile (VSP) data. Because the tube wave is coupled to the formation through which it is traveling, it can perturb the formation across open fractures intersecting the borehole. This squeezing effect can generate secondary tube waves which travel both up and down from the fracture location. Such events can be diagnostic of the presence of open fractures and their amplitude related qualitatively to the length and width, e.g., volume of the fluid-filled fracture space. This effect is generally seen only in shallow formations where the overburdenpressure is lower.

A downhole tool used to repair damaged or collapsed tubing. The tubing broach incorporates a cutter profile that is forced inside the tubing by jarring or hydraulic force to re-form the tubing wall by removing tubing wall material and forcing the tubing wall into place.

A type of batch-treating technique used in corrosion control in which a batch of corrosion inhibitor is displaced through the tubing to the bottom of the well. The well is shut in for 2 to 15 hr and then put back on production.The tubing-displacement technique, also called a kiss squeeze, is used mainly in wells with packers and in gas-lift wells. The treatment could last from a week to several months depending on the specific corrosion inhibitor used.

A downhole tool frequently used in slickline or coiled tubing tool assemblies to confirm or correlate the tool position on depth-sensitive applications. With the end of the production tubing as a known reference point, any error in measurement that may occur in reaching the treatment depth will be significantly less than what may have resulted if measuring from surface.

A system of classifying the material specifications for steel alloys used in the manufacture of tubing.

A device attached to the topmost tubing joint in the wellhead to support the tubing string. The tubing hanger typically is located in the tubing head, with both components incorporating a sealing system to ensure that the tubing conduit and annulus are hydraulically isolated.

A wellhead component that supports the tubing hanger and provides a means of attaching the Christmas tree to the wellhead.

The process of removing and replacing the production tubing in an oil or gas well. The term is commonly used when conducting a major workover of a well.

A single length of the pipe that is assembled to provide a conduit through which the oil or gas will be produced from a wellbore. Tubing joints are generally around 30 ft [9 m] long with a thread connection on each end. The specification of the tubing material, geometry of the tubing, and design of the connection thread are selected to suit the reservoir fluid and wellbore conditions.

A mathematical tool used in production engineering to assess the performance of the completion string by plotting the surface production rate against the flowing bottomhole pressure. The fluid composition and behavior of the fluid phases in the specific completion design will determine the shape of the curve. The TPC is used with the inflow performance relationship to predict the performance of a specific well.

Pressure on the tubing in a well, as measured at the wellhead.

A special perforating gun, or charge, that is designed for limited penetration to allow an inner tubing or casing string to be perforated without damaging a surrounding outer string. These guns often are used in remedial or workover operations in which downhole communication devices, such as sliding sleeves, cannot be opened to allow circulation of well-kill fluids.

(noun) A seal unit consisting of elastomeric or metal-to-metal packing elements that is landed in a packer bore or polished bore receptacle to create a pressure-tight seal between the tubing string and the packer, isolating different zones or preventing annular communication in a completed well.

A downhole tool used to plug the bottom of a production tubing string when pressure testing the assembled string. Slickline-deployed tools and plugs are most commonly used in vertical or slightly deviated wellbores.

The threaded connection used to assemble the tubing string from individual tubing joints. Various tubing thread types have evolved to suit the wellbore conditions and functions required of the tubing string, both during installation and while the well is in production.

The use of tubing, drillpipe or coiled tubing to convey perforating guns to the required depth. Initially, the technique was developed as a means for conveying the gun string on the production tubing, with the guns remaining in the well until they are removed during the first workover. The subsequent popularity of highly deviated and horizontal wells increased the requirement for tubing-conveyed perforating as the only means of gaining access to the perforating depth. The term is often abbreviated as TCP.

A downhole tool used on slickline or coiled tubing operations to identify the end of the production tubing, or similar well features. This information is used to correlate the position of the tool string for accurate placement of depth-critical treatments, plugs or downhole equipment.

A type of subsurface safety valve that is run and retrieved as part of the production tubing string. The TRSV body is integral part of the completion that enables the internal components to be configured to provide near fullbore access through the valve. An external control line is secured to the running string for connection to a surface-control system.

A completion design in which the reservoir fluids are produced through small-diameter casing. The absence of a separate tubing string significantly limits the operating and contingency options available for the well.

A downhole tool used on slickline operations. The tubular jar is a relatively simple mechanical jar that is extended or collapsed by manipulation of the slickline at surface. The impact force delivered by the jar depends on the weight of the tool string above the jar, the density of the wellbore fluid and the stroke length of the jar.

A generic term pertaining to any type of oilfield pipe, such as drill pipe, drill collars, pup joints, casing, production tubing and pipeline.

(noun) A type of sedimentary rock formed by the consolidation and lithification of volcanic ash and pyroclastic material ejected during explosive volcanic eruptions. Tuff beds serve as important stratigraphic markers and chronostratigraphic horizons in basin correlation, and their distinct mineralogy makes them identifiable on gamma ray and other well logs.

A phenomenon of constructive or destructive interference of waves from closely spaced events or reflections. At a spacing of less than one-quarter of the wavelength, reflections undergo constructive interference and produce a single event of high amplitude. At spacing greater than that, the event begins to be resolvable as two separate events. The tuning thickness is the bed thickness at which two events become indistinguishable in time, and knowing this thickness is important to seismic interpreters who wish to study thin reservoirs. The tuning thickness can be expressed by the following formula:Z = VI/2.8 fmax,where Z = tuning thickness of a bed, equal to 1/4 of the wavelengthVI = interval velocity of the targetfmax = maximum frequency in the seismic section.The equation assumes that the interfering wavelets are identical in frequency content and are zero-phase and is useful when planning a survey to determine the maximum frequency needed to resolve a given thickness. Spatial and temporal sampling requirements can then be established for the survey.

Sedimentary deposits formed by turbidity currents in deep water at the base of the continental slope and on the abyssal plain. Turbidites commonly show predictable changes in bedding from coarse layers at the bottom to finer laminations at the top, known as Bouma sequences, that result from different settling velocities of the particle sizes present. The high energy associated with turbidite deposition can result in destruction of earlier deposited layers by subsequent turbidity currents.

An influx of rapidly moving, sediment-laden water down a slope into a larger body of water; also called a density current because the suspended sediment results in the current having a higher density than the clearer water into which it flows. Such currents can occur in lakes and oceans, in some cases as by-products of earthquakes or mass movements such as slumps. The sedimentary deposits that form as the current loses energy are called turbidites and can be preserved as Bouma sequences. Turbidity currents are characteristic of trench slopes of convergent plate margins and continental slopes of passive margins.

A type of fluid flow characterized by swirling or chaotic motion as the fluid moves along the flow path. This is a preferred flow regime for mud removal during primary cementing because it is perceived to result in better removal of mud, especially of mud at the formation wall.

A type of financing arrangement for the drilling of a wellbore that places considerable risk and potential reward on the drilling contractor. Under such an arrangement, the drilling contractor assumes full responsibility for the well to some predetermined milestone such as the successful running of logs at the end of the well, the successful cementing of casing in the well or even the completion of the well. Until this milestone is reached, the operator owes nothing to the contractor. The contractor bears all risk of trouble in the well, and in extreme cases, may have to abandon the well entirely and start over. In return for assuming such risk, the price of the well is usually a little higher than the well would cost if relatively trouble free. Therefore, if the contractor succeeds in drilling a trouble-free well, the fee added as contingency becomes profit. Some operators, however, have been required by regulatory agencies to remedy problem wells, such as blowouts, if the turnkey contractor does not.

To part or break the drillstring downhole due to either fatigue or excessive torque.

Parting or breaking of the drillstring downhole due to fatigue or excessive torque.

A group of 2D seismic lines acquired individually, as opposed to the multiple closely spaced lines acquired together that constitute 3D seismic data.

Seismic data or a group of seismic lines acquired individually such that there typically are significant gaps (commonly 1 km or more) between adjacent lines. A 2D survey typically contains numerous lines acquired orthogonally to the strike of geological structures (such as faults and folds) with a minimum of lines acquired parallel to geological structures to allow line-to-line tying of the seismic data and interpretation and mapping of structures.

A technique for interpreting the results from a spinner flowmeter using two logging runs over the zone of interest, one up and one down. If the two passes are run at the same cable speed, they will overlay below the perforations, where there is no flow. If they were not run at the same speed, the curves are shifted to overlay. Elsewhere, the separation between the curves gives the relative contribution of each zone. Viscosity changes should have a small effect, since they will have the same influence on both passes.The technique is applicable when the flow is single-phase, or else multiphase with a sufficiently homogeneous-flow regime, such as with emulsion or dispersed bubble flow.

The simultaneous flow of both oil and free gas into a wellbore. This is thought to occur through common pore spaces, where the fluids flow simultaneously. In actuality, the situation is much more complicated, and much two-phase flow occurs in a stratified manner, with lighter fluids flowing primarily through the top of a producing zone and heavier ones flowing through the bottom layers.

A vessel that separates the well fluids into gas and total liquid. A two-phaseseparator can be horizontal, vertical or spherical. The liquid (oil, emulsion) leaves the vessel at the bottom through a level-control or dump valve. The gas leaves the vessel at the top, passing through a mist extractor to remove the small liquid droplets in the gas.

The elapsed time for a seismicwave to travel from its source to a given reflector and return to a receiver at the Earth's surface. Minimum two-way traveltime is that of a normal-incidence wave with zero offset.

Families of the paired pressure change and its derivative computed from a model. The model is usually generated from an analytical solution of the diffusion equation with boundary conditions strategically defined to enable observation of theoretical trends in the pressure-transient response. The boundary conditions that can be defined near the well include constant or variable wellbore storage, limited entry (partial penetration), radial composite (damageskin due to permeability alteration), and a fracture extending the cylindrical wellbore to a extended plane. The borehole trajectory can be vertical, angled, or horizontal. The distant boundary conditions include a sealing or partially sealing planar boundary (fault), intersecting faults and rectangular boundaries (sealing or constant pressure). Further, the diffusion equation can be adjusted to accommodate reservoirheterogeneity in the form of dual porosity or layering. Finally, when generated with computer assistance, the type-curve family can account for superposition in time due to flow-rate variations before and even during the transient data acquisition.Originally, type-curve families were printed on specialized (usually log-log) coordinates with dimensionless parameters defining the x and y axes. Today, commercial software can generate the type-curve families on the computer screen, enabling a much more flexible and user-friendly analysis. Further, automated regression (usually least squares) permits an optimized match between the acquired data and a selected model.Type curves have greatly enriched the ability of interpreters to extract potential explanations for transient data trends that differ from the radial-flow behavior required for conventional semilog (Horner buildup) analysis.

A method for quantifying well and reservoir parameters such as permeability, skin, fracture half-length, dual-porosity parameters, and others, by comparing the pressure change and its derivative of the acquired data to reservoir model curve families, called type curves. When a match is found between data and a type curve, the parameters that characterize the behavior of the model providing a match are thereby determined.Originally, type-curve analysis was done manually using only the pressure change. With the introduction of the pressure derivative, the analysis requires matching both pressure change and its derivative. Computer-assisted matching permits rigorous accounting for superposition in time due to flow-rate variations before and even during (in the case of drawdown analysis) the transient data acquisition, as well as providing a continuum of solutions instead of a type-curve family derived from discrete values for the governing parameters.