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65 Cards in this Set
- Front
- Back
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balanced plug |
A plug of cement or similar material placed as a slurry in a specific location within the wellbore and which has set to provide a means of pressure isolation or mechanical platform. For correct placement, the volume of slurry and the displacement fluid must be carefully calculated and measured. The correct volume ensures that the column of fluid in the tubing string is balanced by the column of fluid in the annulus. |
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casing swage |
A short crossover joint used between two sizes or specifications of casing. A circulating swage is an adapter that enables a temporary circulating line to be rigged to the top of the casing string, allowing circulation of fluids to help properly locate the casing string.
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bottomhole static temperature
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The temperature of the undisturbed formation at the final depth in a well. The formation cools during drilling and most of the cooling dissipates after about 24 hours of static conditions, although it is theoretically impossible for the temperature to return to undisturbed conditions. This temperature is measured under static conditions after sufficient time has elapsed to negate any effects from circulating fluids. Tables, charts and computer routines are used to predict BHST as functions of depth, geographic area and various time functions. The BHST is generally higher than the bottomhole circulating temperature, and can be an important factor when using temperature-sensitive tools or treatments. |
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compression-set packer
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A type of downhole packer that is activated or set by applying compressive force to the packer assembly. In most cases, this is achieved with set-down weight from the running string, which is controlled by the driller or operatorobserving the weight indicator on the rig or coiled tubing unit.
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Christmas tree
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An assembly of valves, spools, pressure gauges and chokes fitted to thewellhead of a completed well to control production. Christmas trees are available in a wide range of sizes and configurations, such as low- or high-pressure capacity and single- or multiple-completion capacity.
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conductor pipe
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A short string of large-diameter casing set to support the surface formations. The conductor pipe is typically set soon after drilling has commenced since the unconsolidated shallow formations can quickly wash out or cave in. Where loose surface soil exists, the conductor pipe may be driven into place before the drilling commences.
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carrier fluid
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A fluid that is used to transport materials into or out of the wellbore. Carrier fluids typically are designed according to three main criteria: the ability to efficiently transport the necessary material (such as pack sand during a gravel pack), the ability to separate or release the materials at the correct time or place, and compatibility with other wellbore fluids while being nondamaging to exposed formations.
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churn 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 intermediate flow 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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coning
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The change in oil-water contact or gas-oil contact profiles as a result ofdrawdown 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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cased hole
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A wellbore lined with a string of casing or liner. Although the term can apply to any hole section, it is often used to describe techniques and practices applied after a casing or liner has been set across the reservoir zone, such as cased-hole logging or cased-hole testing.
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cement accelerator
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A chemical additive mixed with cement slurry to reduce the time required for the set cement to develop sufficient compressive strength to enable drilling operations to continue. Accelerators are generally used in near-surface applications in which the temperature is relatively low.
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circulation device
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A completion component, generally included in the lower assembly near the packer, that allows communication between the tubing and annulus. Circulation devices enable the circulation of fluids for well control or kickoff purposes.
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contingency plan
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A key component of the operational planning process that takes account of reasonably foreseeable events that may preventcompletion of normal operations. The formal plans and procedures for any operation should include normal operating procedures, contingency plans and emergency responses.
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casing
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Steel pipe cemented in place during the construction process to stabilize the wellbore. The casing forms a major structural component of the wellbore and serves several important functions: preventing the formation wall from caving into the wellbore, isolating the different formations to prevent the flow orcrossflow of formation fluid, and providing a means of maintaining control of formation fluids and pressure as the well is drilled. The casing string provides a means of securing surface pressure control equipment and downholeproduction equipment, such as the drilling blowout preventer (BOP) orproduction packer. Casing is available in a range of sizes and material grades.
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cement additive
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Chemicals and materials added to a cement slurry to modify the characteristics of the slurry or set cement. Cement additives may be broadly categorized as accelerators, retarders, fluid-loss additives, dispersants, extenders, weighting agents, lost circulation additives and special additives designed for specific operating conditions. Cement additives are commonly available in powder or liquid form, enabling some flexibility in how the cement slurry is prepared.
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cleanup
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A period of controlled production, generally following a stimulation treatment, during which time treatment fluids return from thereservoir formation. Depending on the treatment, the cleanup period can be relatively short and uncomplicated. However, following more complex treatments such as gravel pack or hydraulic fracturing, the cleanup process should be conducted carefully to avoid jeopardizing the long-term efficiency of the treatment.
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continuous gas lift
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An artificial-lift method in which the gas-lift system is operated on a continuous basis to sustain liquid production at an efficient rate.
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casing bowl
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A wellhead component or a profile formed in wellhead equipment in which thecasing hanger is located when a casing string has been installed. The casing bowl incorporates features to secure and seal the upper end of the casing string and frequently provides a port to enable communication with theannulus.
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cement dispersant
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A chemical additive that reduces the cement slurry viscosity to improve fluid flow characteristics. Adequately dispersed cementslurries exhibit improved fluid-loss control, can displace drilling fluid more efficiently and be successfully mixed and pumped at higher densities.
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clear brine
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A water-based solution of inorganic salts used as a well-control fluid during the completion and workover phases of well operations. Brines are solids free, containing no particles that might plug or damage a producing formation. In addition, the salts in brine can inhibit undesirable formation reactions such as clay swelling. Brines are typically formulated and prepared for specific conditions, with a range of salts available to achieve densities ranging from 8.4 to over 20 lbm/gal (ppg) [1.0 to 2.4 g/cmo]. Common salts used in the preparation of simple brine systems include sodium chloride, calcium chloride and potassiumchloride
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control line
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A small-diameter hydraulic line used to operate downhole completion equipment such as the surface controlled subsurface safety valve (SCSSV). Most systems operated by control line operate on a fail-safe basis. In this mode, the control line remains pressurized at all times. Any leak or failure results in loss of control line pressure, acting to close the safety valve and render the well safe.
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casing burst pressure
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The theoretical internal pressure differential at which a joint of casing will fail. The casing burst pressure value is a key consideration in many well-control and contingency operations and is a major factor in the well design process.
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cement extender
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A chemical additive or inert material used to decrease the density or increase the yield of a cement slurry. The slurry yield is typically expressed in cubic feet of slurry per sack of cement. Increasing the yield reduces the cost per volume of cement slurry, while reducing the slurry density reduces the hydrostatic pressure of the cement column, enabling weak zones to be successfully cemented and isolated.
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close in
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To close a valve to stop or isolate fluid flow. The term is most commonly applied to "closing-in the well," meaning isolation of the wellbore by closing the master valve.
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correlate
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To compare and fix measured depths with known features on baseline logs of the wellbore tubulars and the surrounding formation.
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casing collar locator (CCL)
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A downhole tool used to confirm or correlate treatment depth using known reference points on the casing string. The casing collar locator is an electric logging tool that detects the magnetic anomaly caused by the relatively high mass of the casing collar. A signal is transmitted to surface equipment that provides a screen display and printed log enabling the output to be correlated with previous logs and known casing features such as pup joints installed for correlation purposes.
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cement plug
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A balanced plug of cement slurry placed in the wellbore. Cement plugs are used for a variety of applications including hydraulic isolation, provision of a secure platform, and in window-milling operations for sidetracking a new wellbore.
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close-in
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To close a valve to stop or isolate fluid flow. The term is most commonly applied to "closing-in the well," meaning isolation of the wellbore by closing the master valve.
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casing completion
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A completion configuration in which a production casing string is set across thereservoir interval and perforated to allow communication between the formationand wellbore. The casing performs several functions, including supporting the surrounding formation under production conditions, enabling control of fluid production through selective perforation and allowing subsequent or remedial isolation by packers, plugs or special treatments.
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cement retainer
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An isolation tool set in the casing or liner that enables treatments to be applied to a lower interval while providing isolation from theannulus above. Cement retainers are typically used in cement squeeze or similar remedial treatments. A specially profiled probe, known as a stinger, is attached to the bottom of the tubing string to engage in the retainer during operation. When the stinger is removed, the valve assembly isolates the wellbore below the cement retainer.
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corrosion-resistant alloy (CRA)
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A specially formulated material used for completion components in wells likely to present corrosion problems. Corrosion-resistant alloys can be formulated for a wide range of aggressive wellbore conditions. However, cost generally determines the viability of any particular completion design. Alloys with a high chrome content are commonly used for tubing strings.
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casing hanger
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The subassembly of a wellhead that supports the casing string when it is runinto the wellbore. The casing hanger provides a means of ensuring that the string is correctly located and generally incorporates a sealing device or system to isolate the casing annulus from upper wellhead components.
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cement retarder
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A chemical agent used to increase the thickening time of cement slurries to enable proper placement. The need for cement retardation increases with depth due to the greater time required to complete the cementing operation and the effect of increased temperature on the cement-setting process.
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coiled tubing completion
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A completion that utilizes coiled tubing as the production conduit, or as a means of conveying and installing completion equipment or components. Since the coiled tubing string is continuous, problems associated with connections are avoided. Also, the pressure-control equipment used on coiled tubing operations enables work to be safely conducted on live wells.
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cresting
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The change in oil-water or gas-oil contact profiles as a result of drawdownpressures during production. Cresting occurs in horizontal or highly deviated wells and is affected by the characteristics of the fluids involved and the ratio of horizontal to vertical permeability.
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casing hardware
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A generic term used to describe equipment attached to, and run with, thecasing string. Commonly used casing hardware includes guide or float shoes, float or landing collars, centralizers, scratchers and cement baskets. More specialized casing hardware may include stage-cementing collars, differential fill-up equipment and other specialized equipment to help achieve successful placement and cementation of the casing string.
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cement squeeze
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A remedial cementing operation designed to force cement into leak paths in wellbore tubulars. The required squeeze pressure is achieved by carefully controlling pump pressure. Squeeze cementing operations may be performed to repair poor primary cement jobs, isolate perforations or repair damaged casing or liner.
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collar
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A threaded coupling used to join two lengths of pipe such as production tubing,casing or liner. The type of thread and style of collar varies with the specifications and manufacturer of the tubing.
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cross over
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A short subassembly used to enable two components with different thread types or sizes to be connected.
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casing joint
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A length of steel pipe, generally around 40 ft [13 m] long with a threaded connection at each end. Casing joints are assembled to form a casing string of the correct length and specification for the wellbore in which it is installed.
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centralizer
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A device fitted with a hinged collar and bowsprings to keep the casing or liner in the center of the wellbore to help ensure efficient placement of a cement sheath around the casing string. If casing strings are cemented off-center, there is a high risk that a channel of drilling fluid or contaminated cement will be left where the casing contacts the formation, creating an imperfect seal.
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collar locator
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A downhole tool or logging device used to detect and track (log) casing or tubing collars across a zone of interest, typically forcorrelation purposes. Most collar locators detect the magnetic anomaly created by the mass of the steel collar and transmit a signalto surface-display and depth correlation equipment.
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crossflow
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A condition that exists when two production zones with dissimilar pressure characteristics are allowed to communicate during production. Reservoir fluid from the high-pressure zone will flow preferentially to the low-pressure zone rather than up the production conduit unless the production parameters are closely controlled.
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casing pressure
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A term used in well-control operations, typically during the drilling or workover phases of a well, to describe the pressure in thedrillpipe or tubing annulus.
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charged zone
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A formation interval that has become overpressured by the injection of drilling or treatment fluids.
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collar lock
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A type of lock designed to be set in the recess of a tubing collar. Collar locks are compatible only with conventional thread connections where a space exists between the two tubing joints. Premium tubing grades have flush internal surfaces with no space to enable setting of the retaining dogs.
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crossover
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A short subassembly used to enable two components with different thread types or sizes to be connected.
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casing reciprocation
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Movement applied to the casing string during the cementing operation to help in removal of drilling fluid and efficient placement of thecement slurry.
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check valve
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A mechanical device that permits fluid to flow or pressure to act in one direction only. Check valves are used in a variety of oil and gas industry applications as control or safety devices. Check valve designs are tailored to specific fluid types and operating conditions. Some designs are less tolerant of debris, while others may obstruct the bore of the conduit or tubing in which the check valve is fitted.
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collar log
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A log showing the depth or relative position of casing or tubing collars that is used to correlate depth for depth-sensitive applications such as perforating or isolation treatments. Indications are provided by a collar locator tool and correlations are made with previousbaseline logs, such as the gamma ray log, or the casing or tubing running tally prepared during the installation process.
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crossover service tool
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A specialized tool, frequently used in gravel-pack operations, that enables the circulation of the treatment fluid (slurry) from the internal flow path of the tool string into the annulus area to be packed. The returned carrier fluid enters the internal flow path at the base of the tool before crossing over to the annulus above the packer assembly, isolating the annulus.
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casing shoe test
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A pressure test applied to the formation directly below a casing shoe. The test is generally conducted soon after drilling resumes after an intermediate casing string has been set. The purpose of the test is to determine the maximum pressures that may be safely applied without the risk of formation breakdown. The results of the test are used to design the mud program for the subsequent hole section and to set safe limits on casing shut-in or choke pressures for well-control purposes.
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chelating agent
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A chemical used to bind metal ions to form a ring structure. Chelating agents stabilize or prevent the precipitation of damaging compounds. In the oil field, chelating agents are used in stimulation treatments and for cleaning surface facilities. They are also used to treat or remove scale or weighting agents in reservoir drilling fluids. During acid or scale-removal treatments, various compounds may be dissolved in the treatment fluid. As the acid reacts and the pH increases, reaction products may precipitate as a gelatinous, insoluble mass. Should this occur within the formation matrix, it is almost impossible to remove and permanent permeability damagemay occur. Chelating agents prevent precipitation by keeping ions in a soluble form until the treatment fluid can be flowed back from the formation during cleanup. Typical oilfield chelating agents include EDTA (ethylenediamine tetraacetic acid), HEDTA (hydroxyethylenediamine triacetic acid), NTA (nitriolotriacetic acid) and citric acid.
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commingled flow
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A term used to describe the flow pattern where two or more fluid phases may be present in a relatively even distribution. The flow rate and conduit geometry may cause an apparent mixing of the phases. However, if the flow characteristics are changed through flow rate or conduit geometry, fluid separation may occur. Fine solids also may be entrained in a commingled flow. Commingled flow may also describe the production of fluid from two or more separate zones through a single conduit.
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crown valve
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The topmost valve on a Christmas tree that provides vertical access to the wellbore.
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casing spool
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A wellhead component used in flanged wellhead assemblies to secure the upper end of a casing string. Casing spools or bowls are available in a wide range of sizes and pressure ratings and are selected to suit the specific conditions.
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chemical diverter
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A chemical agent used in stimulation treatments to ensure uniform injection over the area to be treated. Chemical diverters function by creating a temporary blocking effect that is safely cleaned up following the treatment, enabling enhanced productivity throughout the treated interval. In matrix acidizing of injection wells, benzoic acid is used as a chemical diverter, while oil-soluble resins are employed in production wells. Both compounds are slightly soluble or inert in the acidic medium [HCl], but after functioning as diverters, they dissolve with water injection or oil production, respectively. Stable, viscous foams generated in the rock matrix are also considered to be chemical diverters.
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complete a well
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To perform activities in the final stages of well construction to prepare a well for production. The well is completed once zones of interest have been identified.
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crystallization temperature
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The temperature at which crystals will appear in a brine solution of a given density as it cools. In preparing oilfield brines, the crystallization temperature can be used to indicate the maximum saturation (density) achievable for a brine solution at a given temperature.
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datum
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A depth reference point, typically established at the time the well is completed, against which subsequent depth measurements should be corrected or correlated.
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disposal well
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A well, often a depleted oil or gas well, into which waste fluids can be injected for safe disposal. Disposal wells typically are subject to regulatory requirements to avoid the contamination of freshwater aquifers.
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downstream
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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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drillable packer
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A packer assembly that can be removed from the wellbore only by drilling or milling. Drillable packers, and similar tools such asbridge plugs, are typically made from cast iron, aluminum, plastic or similar brittle materials.
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depleted zone
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An isolated section of reservoir in which the pressure has dropped below that of adjacent zones or the main body of the reservoirformation.
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drain hole
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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 ofpressure within a nonpressure area, such as may occur in the event of a leak in a pressure housing within a tool assembly. |
