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62 Cards in this Set
- Front
- Back
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depth control |
The procedures and equipment used to measure and correlate depth to ensure that a treatment is applied at the correct position within the wellbore. |
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down stream
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Pertaining to equipment, facilities or systems that are located in the production train after the surface choke or Christmas tree.
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drainhole
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A hole or short conduit through which fluids can flow. In equipment applications, a drainhole is generally made to avoid the buildup of pressure within a nonpressure area, such as may occur in the event of a leak in a pressurehousing within a tool assembly. |
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dry gas
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Gas produced from a well that produces little or no condensate or reservoir liquids. The production of liquids from gas wells complicates the design and operation of surface process facilities required to handle and export the produced gas.
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depth reference point
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A point within the wellbore from which accurate depth measurements can be made, such as the end of the tubing string, or a nipple or similar completion component.
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downhole gauge
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A pressure gauge, typically run on slickline, used to measure and record downhole pressure. Downhole gauges are commonly used in assessing the downhole pressure under various flowing conditions, the basis of pressure transient analysis.
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drift
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An accurately machined device that is pulled through the casing, tubulars and completion components to ensure minimum-diameter specifications are within tolerance, as described in definition 2. While this tool is usually of a short length, the well planner may specify a special drift that either has a longer length or a nonstandard outside diameter. The large-diameter casing drifts are frequently known as "rabbits."
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dual completion
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A single wellbore having tubulars and equipment that enable production from two segregated zones. In most cases, two tubing strings will be used to provide the necessary level of control and safety for the fluids from both zones. However, in some simple dual completions, the second or upper zone is produced up the tubing-casing annulus.
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electric submersible pump
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An artificial-lift system that utilizes a downhole pumping system that is electrically driven. The pump typically comprises several staged centrifugal pump sections that can be specifically configured to suit the production and wellbore characteristics of a given application. Electrical submersible pump systems are a common artificial-lift method, providing flexibility over a range of sizes and output flow capacities.
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expansion joint
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A device or completion component designed to enable relative movement between two fixed assemblies in the event of thermal expansion or contraction. The forces generated by thermal expansion or contraction can be significant. Expansion joints within the completion assembly prevent any movement or forces being transmitted to fixed components such as packers or tubing hangers.
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external pulling tool
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A downhole tool used to pull or retrieve temporary plugs or similar equipment. The external pulling tool engages on the external surfaces of the item to be retrieved.
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external upset
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A type of tubing connection in which the external diameter of the tubing joint is larger adjacent to the tubing connection to provide the necessary strength. The internal tubing surface is flush to enable good fluid-flow characteristics.
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equalizing valve
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A device that is operated to equalize the pressure across a valve, plug or similar pressure or fluid isolation barrier. The operating mechanism on many pressure-sealing devices is rendered inoperable once the mechanism has been activated by pressure. In such cases, the pressure across the pressure barrier must be equalized before the barrier can be removed.
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expendable plug
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A temporary plug, inserted in the completion assembly before it is run, to enable pressure testing of the completed string. With the operation complete, the expendable plug can be pumped out of the assembly, thereby avoiding a separate retrieval run.
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filtered brine
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A completion or workover fluid that has been treated to remove debris and fine particles that may cause near-wellbore damage if allowed to enter the reservoir formation.
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float shoe
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A rounded profile component attached to the downhole end of acasing string. An integral check valve in the float shoe prevents reverse flow, or U-tubing, of cement slurry from the annulus into the casing or flow of wellbore fluids into the casing string as it is run. The float shoe also guides the casing toward the center of the hole to minimize hitting rock ledges or washouts as the casing is run into the wellbore. The float shoe reduces hook weight. With controlled or partial fill-up as the string is run, the casing string can be floated into position, avoiding the need for the rig to carry the entire weight of the casing string. The outer portions of the float shoe are made of steel and generally match the casing size and threads, although not necessarily the casing grade. The inside (including the taper) is usually made of cement or thermoplastic, since this material must be drilled out if the well is to be deepened beyond the casing point.
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formation damage
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A general term to describe the reduction in permeability to the near-wellbore area of a reservoir formation. There are several recognized damage mechanisms, such as the invasion of incompatible fluids swelling the formation clays, or fine solids from dirty fluids plugging the formation matrix. Because formation damage can significantly affect the productivity of any well, adequate precautions should be exercised to avoid damage during all phases in the life of a well.
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frac job
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Another term for hydraulic fracturing, a stimulation treatment routinely performed on oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of formation and bypasses any damage that may exist in the near-wellbore area.
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fines migration
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The movement of fine clay, quartz particles or similar materials within the reservoir formation due to drag forces during production. Fines migration may result from an unconsolidated or inherently unstable formation, or from use of an incompatible treatment fluid that liberates fine particles. Unlike sand migration that is best stabilized, the material mobilized in fines migration should be produced to avoid near-wellbore damage. Fines migration causes particles suspended in the produced fluid to bridge the pore throats near the wellbore, reducing well productivity. Fines can include different materials such as clays (phyllosilicates smaller than 4 microns) and silts (silicates or aluminosilicates with sizes ranging from 4 to 64 microns). Kaolinite and illite are the most common migrating clays.Damage created by fines usually is located within a radius of 3 to 5 ft [1 to 2 m] of the wellbore, but can also occur in gravel-pack completions. In sandstone formations, hydrofluoric acid [HF] mixtures are used to dissolve fines. Incarbonate formations, the goal is not to dissolve but rather to disperse fines in the wormholes, so hydrochloric [HCl]acid is used as the treatment fluid.
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flow check
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A test performed to ensure stable well conditions or the integrity of a plug, valve or flow-control device. In most cases, the flow check involves observing stable fluid levels or conditions for a prescribed period.
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formation fluid
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Any fluid that occurs in the pores of a rock. Strata containing different fluids, such as various saturations of oil, gas and water, may be encountered in the process of drilling an oil or gas well. Fluids found in the target reservoirformation are referred to as reservoir fluids.
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fracture
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To perform a stimulation treatment, which is routine for oil and gas wells in low-permeability reservoirs. Specially engineered fluids are pumped at high pressure and rate into the reservoir interval to be treated, causing a vertical fracture to open. The wings of the fracture extend away from the wellbore in opposing directions according to the natural stresses within the formation. Proppant, such as grains of sand of a particular size, is mixed with the treatment fluid to keep the fracture open when the treatment is complete. Hydraulic fracturing creates high-conductivity communication with a large area of formation and bypasses any damage that may exist in the near-wellbore area.
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fixed choke
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A device used to control the flow of fluids by directing flow through a restriction or hole of a fixed size. The fluid characteristics and the pressure differential across the choke determine the flow rate through a fixed choke.
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flow coupling
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A relatively short, heavy-walled completion component installed in areas where turbulence is anticipated. The additional wall thickness prevents early failures due to erosion in the turbulent flow area. Flow couplings are typically installed above and below completion components, such as landing nipples, that may affect the flow.
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formation fracture pressure
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Pressure above which injection of fluids will cause the rock formation to fracture hydraulically.
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fracturing fluid
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A fluid injected into a well as part of a stimulation operation. Fracturing fluids for shale reservoirs usually contain water, proppant, and a small amount of nonaqueous fluids designed to reduce friction pressure while pumping the fluid into the wellbore. These fluids typically include gels, friction reducers, crosslinkers, breakers and surfactants similar to household cosmetics and cleaning products; these additives are selected for their capability to improve the results of the stimulation operation and the productivity of the well.
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flag joint
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A joint of tubing or casing included in the string at a known position to provide a reference point for further operations. A short pup joint that registers clearly in a collar locator log is a common flag joint.
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fluid invasion
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A general term to describe the presence of a particular fluid in an undesirable area, such as the movement of drilling mud into a section of the reservoir formation.
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formation pressure
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The pressure within the reservoir rock. The formation pressure value can be further categorized as relating toflowing well or shut-in conditions.
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free water
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The aqueous phase that separates from a slurry or mixture of fluids. In cementing operations, free water is undesirable since channels tend to form through the set cement, providing potential gas migration paths. When processing reservoir fluids, the water that separates easily under gravity separation is known as free water. In some cases, additional water may be locked in an emulsion, contributing to the aqueous phase but not available as free water.
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flange
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A connection profile used in pipe work and associated equipment to provide a means of assembling and disassembling components. Mostoilfield flanges feature a bolt-hole pattern to allow the joint to be secured and a gasket profile to ensure a pressure-tight seal. The design and specification of a flange relates to the size and pressure capacity of the equipment to which it is fitted.
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fluid-loss additive
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A chemical additive used to control the loss of fluid to the formation through filtration. In cementing operations, loss of the aqueous phase can severely affect the performance of the slurry and set cement. In almost any operation, loss of fluid to the reservoir formation carries a high risk of permeability damage.
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frac balls
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Another term for ball sealers, 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.
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froth flow
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A multiphase flow regime in near-vertical pipes in which large, irregular slugs of gas move up the center of the pipe, usually carrying droplets of oil or water with them. Most of the remaining oil or water flows up along the pipe walls. The flow is relatively chaotic, producing a frothy mixture. Unlike slug flow, neither phase is continuous. The gas slugs are relatively unstable, and take on large, elongated shapes. Also known as transition flow, this flow is an intermediateflow condition between slug flow and mist flow, and occurs at relatively high gas velocity. As the gas velocity increases, it changes into annular flow. |
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flange up
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The process of assembling flanged components such as pressure-control equipment.
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flush joint
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A type of tubing connection in which the internal or external surfaces are the same diameter throughout the tubing joint. Internal flush joints are most common, offering no restriction to fluid flow. Externally flush joints are typically used in more specialized applications, such aswashover pipe for fishing operations, to allow adequate outer diameter (OD) clearance.
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frac fluid
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An abbreviation for fracturing fluid, a fluid injected into a well as part of a stimulation operation. Fracturing fluids forshale reservoirs usually contain water, proppant, and a small amount of nonaqueous fluids designed to reduce friction pressure while pumping the fluid into the wellbore. These fluids typically include gels, friction reducers, crosslinkers, breakers and surfactants similar to household cosmetics and cleaning products; these additives are selected for their capability to improve the results of the stimulation operation and the productivity of the well.
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fullbore
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A description of the internal area and surfaces of a tool or tubular assembly through which there is an unimpeded internal diameter. In some cases, fullbore is used to describe the form of a nominal internal diameter that extends over the length of the tool or interval without any variation. In other applications, the term simply implies an ability topass a ball or similar item of a stated drift diameter through the assembly.
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float collar
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A component installed near the bottom of the casing string on whichcement plugs land during the primary cementing operation. It typically consists of a short length of casing fitted with a check valve. This device may be a flapper-valve type, a spring-loaded ball valve or other type. The check-valve assembly fixed within the float collarprevents flowback of the cement slurry when pumping is stopped. Without a float collar, the cement slurry placed in the annulus could U-tube, or reverse flow back into the casing. The greater density of cement slurries than the displacement mud inside the casing causes the U-tube effect.
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gas bearing
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Relating to a formation or interval containing gas, either dissolved in the formation fluid or as free gas. The term is occasionally used to describe wellbore fluids containing dissolved gas.
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gas lift mandrel
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A gas-lift system component that is assembled with the production tubing string to provide a means of locating gas-lift valves. The position or depth of the gas lift valves is crucial to the efficient operation of the entire system. Consequently, proper assembly of the gas lift mandrels within the completion tubulars is essential. A port in the gas-lift mandrel provides communication between the lift-gas supply in the tubing annulus and the production-tubing conduit.
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gauge pressure
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The measured pressure within a system in which the pressure gauge reads 0 psi at nominal atmospheric pressure.
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gas cap
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The gas that accumulates in the upper portions of a reservoir where the pressure, temperature and fluid characteristics are conducive to free gas. The energy provided by the expansion of the gas cap provides the primary drive mechanism for oil recovery in such circumstances.
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gas lift valve
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A valve used in a gas-lift system to control the flow of lift gas into the production tubing conduit. The gas-lift valve is located in the gas-lift mandrel, which also provides communication with the lift gas supply in the tubing annulus. Operation of the gas lift valve is determined by preset opening and closing pressures in the tubing or annulus, depending on the specific application.
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gasdrive
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A primary recovery mechanism for oil wells containing dissolved and free gas, whereby the energy of the expanding gas is used to drive the oil from the reservoir formation into the wellbore.
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gauge ring
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A precisely machined test device, typically fabricated from steel or similar durable material, having a specified internal or external diameter. The gauge ring is used to confirm the dimensional compatibility of tools and equipment that must pass through restrictions of a certain diameter.
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gas coning
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Change in the gas-oil contact profile as a result of drawdown pressures during production. Coning occurs in vertical or slightly deviated wells and is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability.
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gas lock
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A condition in pumping and processing equipment caused by the induction of free gas. The compressible gas interferes with the proper operation of valves and other pump components, preventing the intake of fluid.
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gas-lift mandrel
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A gas-lift system component that is assembled with the production tubing string to provide a means of locating gas-lift valves. The position or depth of the gas lift valves is crucial to the efficient operation of the entire system. Consequently, proper assembly of the gas lift mandrels within the completion tubulars is essential. A port in the gas-lift mandrel provides communication between the lift-gas supply in the tubing annulus and the production-tubing conduit.
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GOC
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Abbreviation for gas-oil contact, the interface between the gas and oil phases present in a reservoir formation. During the production of a well, the GOC may move, resulting in undesirable production conditions such as a high proportion of gas that may be too much for surface processing facilities. Monitoring the gas-oil and oil-water contacts is a key element of good reservoir management practices.
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gas drive
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A primary recovery mechanism for oil wells containing dissolved and free gas, whereby the energy of the expanding gas is used to drive the oil from the reservoir formation into the wellbore.
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gravel pack
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A sand-control method used to prevent production of formation sand. In gravel pack operations, a steel screen is placed in the wellbore and the surrounding annulus packed with prepared gravel of a specific size designed to prevent the passage of formation sand. The primary objective is to stabilize the formation while causing minimal impairment to well productivity.
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gas injection
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A reservoir maintenance or secondary recovery method that uses injected gas to supplement the pressure in an oil reservoir or field. In most cases, a field will incorporate a planned distribution of gas-injection wells to maintainreservoir pressure and effect an efficient sweep of recoverable liquids.
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gas separator
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A device used to separate entrained gas from production liquids. Surface processing facilities generally use gas separators to render the liquids safe for further processing or disposal. Gas-separation equipment is also used in downhole applications, such as the protection of pumping equipment against gas lock by separating and redirecting free gas at the pump suction or inlet.
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gas-oil contact
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The interface between the gas and oil phases present in a reservoir formation. During the production of a well, the GOC may move, resulting in undesirable production conditions such as a high proportion of gas that may be too much for surface processing facilities. Monitoring the gas-oil and oil-water contacts is a key element of good reservoir management practices. |
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gravel pack screen
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A metal filter assembly used to support and retain the sand placed during gravel pack operations. A range of sizes and screenconfigurations is available to suit the characteristics of the wellbore,production fluid and the formation sand.
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gas lift
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An artificial-lift method in which gas is injected into the productiontubing to reduce the hydrostatic pressure of the fluid column. The resulting reduction in bottomhole pressure allows the reservoir liquids to enter the wellbore at a higher flow rate. The injection gas is typically conveyed down the tubing-casing annulus and enters the production train through a series of gas-lift valves. The gas-lift valveposition, operating pressures and gas injection rate are determined by specific well conditions. |
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gas well
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A well that primarily produces natural gas.
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gate valve
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A type of valve that incorporates a sliding gate to block fluid flow. The design of the valve operating and sealing systems typically requires that gate valves should be operated either fully open or fully closed.
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gravel-pack screen
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A metal filter assembly used to support and retain the sand placed during gravel pack operations. A range of sizes and screenconfigurations is available to suit the characteristics of the wellbore,production fluid and the formation sand. |
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HF
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A poisonous liquid acid composed of hydrogen and fluorine. Hydrofluoric acid [HF] is used primarily because it is the only common, inexpensive mineral acid that can dissolve siliceous minerals. HF is typically mixed withhydrochloric acid [HCl] or organic acid to keep the pH low when it spends, thereby preventing detrimental precipitates. These mixtures, also called mud acids, are considered the main fluid in a sandstone acid treatment because they remove formation damage. Hydrofluoric acid should not be used in sandstone formations with highcarbonate content because of the high risk of calcium fluoride precipitation [CaF2]. |
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hot oiling
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Circulation of heated fluid, typically oil, to dissolve or dislodge paraffin deposits from the production tubing. Such deposits tend to occur where a large variation in temperature exists across the producing system. |
