Glossary

Mechanical surface wear on the coiled tubing string caused by frictional contact with the wellbore, completion components, or pressure control equipment. Often presents as a combination of galling and abrasive metal loss, typically oriented longitudinally along the pipe body. Severity and pattern vary with the wear source, dogleg severity, and contact loads.

A matrix or near-wellbore treatment in which acid or other reactive fluids are spotted downhole to dissolve formation damage, scale, or carbonate material and restore permeability. Coiled tubing conveyance allows precise depth-targeted placement of treatment fluids across the producing interval, making it well suited for restoring deliverability in mature or damaged wells.

A stimulation technique in which coiled tubing is run in hole with an inflatable packer or straddle-type bottomhole assembly to isolate a discrete interval, while the frac fleet pumps treatment fluid down the CT/casing annulus. This enables selective, stage-by-stage fracturing of specific zones without plug-and-perf operations.

The velocity of fluid returns moving up the annulus between the CT string and the casing or tubing I.D. A governing parameter in cleanout design — annular velocity must exceed the particle slip velocity of the fill material to achieve effective solids transport to surface, particularly in horizontal and deviated wellbores.

Permanent, progressive increase in CT outside diameter caused by cyclic bending under internal pressure. Diameter growth is monitored against retirement criteria because it thins the wall, accelerates fatigue accumulation, and can interfere with stripper sealing and BOP ram fit.

The angled (skewed) factory weld joining flat strip sections of differing wall thickness during coiled tubing manufacture, creating the taper transitions in a string. Bias welds historically represent localized fatigue-life derating points, which tapered-strip technologies such as SMARTaper™ are designed to eliminate.

A BOP ram fitted with flat, non-ported sealing elements designed to close and seal across an open wellbore when no tubular is present. In a CT stack, blind rams are typically actuated after the shear rams have severed the string, completing full wellbore closure.

A hydraulically actuated well control device comprising a stack of ram-type preventers (pipe, slip, shear, and blind) that provides secondary well control. The BOP allows the crew to seal the wellbore, secure the work string, and shut in the well in the event of an influx or loss of primary barrier integrity.

The configuration of downhole tools made up on the end of the coiled tubing string — e.g., connectors, check valves, disconnects, motors, mills, jetting nozzles, or logging tools. BHA design is application-specific and engineered for the intervention objective, wellbore geometry, and anticipated downhole conditions.

Lateral deformation of the CT string under compressive loading in the wellbore. Sinusoidal buckling initiates first as a snaking waveform; with increased compression it transitions to helical buckling, where the string spirals against the casing wall, sharply increasing wall contact force and friction and ultimately leading to lockup.

The internal pressure rating at which pipe body yield or failure is predicted, derived from wall thickness, O.D., and material yield strength (per API 5ST and Barlow-based calculations, with applicable design factors). Burst capacity degrades with wall loss and diameter growth over string life.

The placement of cement slurry via coiled tubing to achieve zonal isolation, set balanced plugs, or perform squeeze operations into perforations or the formation. CT cementing provides accurate depth control and allows spotting slurry at discrete intervals within the wellbore.

Barrier valves — typically dual flapper type for redundancy — run in the CT connector or BHA to permit pumping down the string while preventing wellbore fluids from flowing back up the coil. Internal check valves form part of the well control barrier envelope during live-well intervention.

A fill-removal intervention in which fluid or nitrogen is circulated through the CT string to lift sand bridges, proppant fill, scale, paraffin, or other hydrocarbon deposits from the wellbore, restoring flow area and access to the producing interval.

Continuously milled steel line pipe manufactured, externally coated in-line, and spooled onto reels prior to final testing. Because it deploys in continuous lengths, it eliminates field girth welds — reducing installation time and weld-related integrity risk. Common applications include well tie-ins, flowlines, and gathering pipelines.

The mechanical interface securing the BHA to the end of the CT string, typically a grapple (external slip), dimple, or roll-on type. The connector must transmit tension, compression, torque, and pressure integrity between the coil and the toolstring, and its pull rating is a design input for fishing and jarring contingencies.

The drum assembly on a CT unit — skid- or trailer-mounted — used to store, spool, and deploy the coiled tubing string. The reel maintains back-tension against the injector head and typically incorporates a levelwind and swivel for fluid circulation while spooling.

The complete surface package required to run coiled tubing operations, typically comprising the control cabin, reel and CT string, injector head and gooseneck, hydraulic power pack, and well control stack (stripper and BOP).

The external differential pressure rating at which the pipe body is predicted to collapse (ovalize and flatten). CT collapse resistance is strongly degraded by ovality, applied axial tension, and wall loss — a key consideration when the coil is evacuated (e.g., nitrogen displacement) against high annulus pressure.

The operator’s console for the CT unit, generally positioned with line-of-sight to the reel and injector head. All primary functions — injector speed and direction, reel tension, stripper and BOP actuation, and circulating parameters — are monitored and controlled from the cabin.

An engineered alloy chemistry formulated to resist corrosive attack from downhole environments such as H₂S, CO₂, and chlorides. CRA tubulars extend service life in sour or otherwise corrosive wellbores where carbon steel would suffer accelerated degradation.

The system and process for tracking BHA depth during a CT job. Surface depth is measured by friction or optical encoder wheels at the injector, then corrected for tubing stretch, thermal effects, and residual bend; precise depth control for perforating, setting plugs, or spotting fluids is confirmed by correlating to known downhole references such as casing collars (CCL) or tubing end locators.

The rate of change of wellbore inclination and azimuth, expressed in degrees per 100 ft (or per 30 m). High DLS increases CT bending stress, wall contact force, and drag, reducing reach and accelerating localized fatigue and wear.

A positive displacement (Moineau-type) mud motor run in the CT BHA that converts circulating fluid hydraulic energy into bit or mill rotation. The workhorse of CT milling and drilling operations; motor differential pressure at surface is the primary real-time indicator of weight-on-bit and mill loading.

Global Tubing’s technically advanced, cost-efficient coiled tubing product line engineered for demanding downhole service environments requiring enhanced fatigue and corrosion performance.

Coiled tubing manufactured or retrofitted with an electric conductor (e-line) installed inside the string, enabling real-time downhole telemetry, powered tools, and surface readout for CT logging, milling optimization, and intelligent intervention applications.

A non-destructive electromagnetic inspection method used on coiled tubing to detect wall anomalies, cracks, pitting, and dimensional irregularities in real time, typically during manufacturing or as the string runs through inspection heads at the wellsite.

The cumulative low-cycle plastic deformation a CT string accrues from repeated bend-straighten cycles over the reel, gooseneck, and injector — often under internal pressure. Fatigue life is tracked and modeled per string segment and is the primary determinant of safe working life and retirement criteria.

The Metric used to quantify plastic deformation sustained by coiled tubing operations.

An intervention to engage and retrieve equipment, tools, or wire lost or stuck downhole (the “fish”). CT fishing employs purpose-built BHAs — overshots, spears, and grapples with profiles matched to the fish neck — to latch, jar, and recover the obstruction.

A coiled tubing string processed to remove the internal weld flash (the upset bead formed at the longitudinal seam). Removing the flash improves internal surface finish and flow characteristics and enhances resistance to preferential corrosion at the weld line.

A polymer additive (commonly polyacrylamide-based) blended into treatment or circulating fluids to reduce turbulent-flow friction pressure inside the CT string, lowering required pump pressure and enabling higher rates through small-I.D. coil; also a core component of slickwater frac fluids.

An unloading operation in which nitrogen (or CO₂) is injected through the CT string to lighten the fluid column, reduce hydrostatic pressure on the formation, and kick off or restore production — commonly applied to liquid-loaded or high-water-cut wells.

The curved guide assembly mounted atop the injector head that directs the CT string from the reel into the injector chains at a controlled bend radius. The gooseneck radius is a key input in string fatigue calculations.

The specified minimum yield strength classification of coiled tubing material per API 5ST — e.g., CT80, CT90, CT100, CT110, where the number denotes minimum yield in ksi. Grade selection balances tensile capacity and pressure ratings against sour service (NACE MR0175/ISO 15156) hardness limitations.

The profiled inserts mounted on the injector head drive chains that clamp the CT string between opposed chain runs, transmitting traction force for RIH/POOH and snubbing. Block profile must match string O.D.; worn or mismatched blocks cause slippage, crushing, or surface damage to the coil.

The condition in which compressive load on a helically buckled CT string generates wall contact friction faster than it advances the string, such that additional injector weight produces no further downhole progress. Lockup defines the practical reach limit of a CT string in a given lateral and is predicted by tubing forces modeling.

A stimulation technique in which fluid carrying proppant (sand or engineered ceramics) is pumped at pressures above the formation fracture gradient to initiate and propagate fractures, creating high-conductivity flow paths and increasing effective permeability in the target formation.

A pressure integrity test in which the CT string is filled with fluid and held at a specified internal test pressure for a defined duration to verify pressure containment, joint integrity, and fitness for service prior to or during operations.

The traction unit mounted above the wellhead stack that grips the CT string between opposed drive chains and controls run-in-hole (RIH) and pull-out-of-hole (POOH) speed and direction. It provides both snubbing force against wellhead pressure and pulling capacity, and is operated from the control cabin via a closed-loop hydraulic system.

A BHA-terminating tool with machined ports that convert pump rate into high-velocity fluid jets for wellbore cleanouts, scale removal, and fill agitation. Port sizing is engineered to balance jetting impact force against system friction pressure and annular velocity requirements.

An unplanned influx of formation fluids (gas, oil, or water) into the wellbore that occurs when bottomhole pressure falls below formation pore pressure — i.e., the well becomes underbalanced due to drawdown or loss of hydrostatic head. An uncontrolled kick can escalate into a well control event or blowout if not detected and shut in.

The measured length of the horizontal section of a wellbore, from heel to toe. The lateral is typically the stimulated interval in multistage horizontal fracturing programs and drives CT reach and extended-reach design considerations.

The traversing guide assembly on the reel that lays the CT string evenly across the drum in successive wraps during spooling. Proper levelwind alignment prevents stacking, crossovers, and mechanical damage to the coil, and maintains consistent back-tension geometry.

The acquisition of downhole measurements — bottomhole pressure and temperature, production profiles, casing/cement integrity — by conveying logging tools on coiled tubing, often with an installed e-line providing real-time surface readout. CT conveyance enables logging in horizontal and highly deviated wellbores where gravity-conveyed wireline cannot reach.

Pressure-rated pipe sections installed in the stack above the BOP that provide the vertical space needed to deploy and retrieve the BHA into and out of a live well under pressure. Riser length must accommodate the full toolstring between the stripper and the swab valve.

Mechanical removal of downhole obstructions — frac plugs, cement, scale, fish, or collapsed tubulars — using a rotating mill driven by a downhole motor on CT. Mill dress (junk, tapered, flat-bottom) is selected for the target material, with returns circulated to surface and monitored for millout confirmation.

The standardized upper-BHA package run directly below the CT connector, typically integrating dual flapper check valves, a hydraulic or tension-actuated disconnect, and a circulation/burst disc sub. The MHA consolidates well control, contingency release, and emergency circulation functions in a single assembly.

The use of cryogenically stored, vaporized nitrogen pumped through the CT string for energized cleanouts, underbalanced operations, well unloading and kickoff, pressure testing, and gas-assisted fluid displacement. Nitrogen’s inert, non-flammable behavior makes it the standard gas phase for CT interventions.

Drilling performed with a coiled tubing unit using a steerable, motor-driven BHA, typically with e-line telemetry through the CT string for directional control and real-time downhole data. Applied in underbalanced drilling, re-entries, and slim-hole applications.

The nominal external diameter of a tubular, measured across the pipe body. A primary specification for CT strings, governing stack-up compatibility, annular clearance, and pressure/tension ratings.

The deviation of the CT cross-section from circular, expressed as the difference between maximum and minimum measured diameters relative to nominal. Ovality accumulates with bending cycles and mechanical damage, and directly degrades collapse resistance and sealing performance in the stripper.

A BOP ram with sealing elements profiled to close around a specific tubular O.D., sealing the annulus between the wellbore and the work string while leaving the string intact and full-bore.

A post-frac intervention, typically following plug-and-perf completions, in which a CT-conveyed motor-and-mill BHA drills out composite or dissolvable frac plugs and circulates the debris to surface, reestablishing full wellbore access for production.

The diesel- or electric-driven hydraulic power unit (HPU) that supplies hydraulic pressure and flow to the CT unit’s injector, reel, and pressure control functions.

The stack-up of well control components — stripper/packer, BOP, lubricator risers, and associated connections — that maintains a dynamic and static seal on the wellbore, enabling live-well intervention under pressure.

The first, normally closed pressure-containment element between wellbore pressure and the atmosphere during intervention — e.g., the stripper/packer element sealing dynamically around the moving CT string. Barrier philosophy requires the primary barrier to be continuously energized during live-well work.

The operation of retrieving the CT string and BHA from the wellbore back to surface, spooling the string onto the reel.

A surface test fixture that clamps around the assembled BHA connections, allowing pressure testing of the toolstring and connector integrity before RIH without pressuring the full CT string — reducing rig-up time and unnecessary fatigue cycling of the coil.

A contingency BHA component — hydraulically actuated (ball-drop) or tension-activated — that allows the CT string to be released from a stuck toolstring at a predetermined point, leaving a standard fishing neck for subsequent recovery operations.

The permanent curvature retained in the CT string after it leaves the reel and passes through the injector, resulting from plastic deformation during spooling. Residual bend influences downhole drag, standoff, depth accuracy, and the orientation tendency of the BHA in the lateral.

The operation of deploying the CT string and BHA from surface into the wellbore to the target depth.

The continuous longitudinal weld formed during tube milling — by high-frequency induction (HFI) or electric resistance welding (ERW) — that closes the rolled strip into a tube. Seam weld quality is verified by full-length NDE and governs the pressure integrity of the finished coil.

A normally open, independently actuated pressure-containment element — typically the BOP rams — that is closed to secure the well if the primary barrier fails or requires maintenance under pressure.

A BOP ram fitted with hardened cutting blades capable of severing the CT string (and internal wireline, where rated). Actuated as a last-resort well control measure, shearing the string allows the blind rams to close and achieve full wellbore shut-in.

A BOP ram fitted with gripping inserts (slips) that close on and anchor the CT string, preventing axial movement — both upward ejection under wellbore pressure and downward slippage. Commonly actuated in conjunction with pipe rams during a well control event.

Global Tubing’s patented tapered-string coiled tubing technology that eliminates bias-weld fatigue spikes, extending usable running length. The design increases horizontal reach, adds wall thickness and strength in high-fatigue sections of the string, and optimizes overall string weight.

The reel or shipping drum on which the CT string is stored, transported, and deployed during operations. Spool core diameter is a fatigue design parameter, as it sets the bend radius the string experiences each cycle.

The condition and operation of forcing tubing into a live well against wellbore pressure when the upward pressure-area force exceeds string weight (pipe-light). The CT injector provides snub force through the gripper chains; the pipe-light/pipe-heavy transition point is a key well control planning parameter.

Operating environments containing hydrogen sulfide at partial pressures above NACE MR0175/ISO 15156 thresholds, where susceptible steels risk sulfide stress cracking (SSC). Sour service dictates material grade, hardness limits, and handling requirements for CT strings and pressure control equipment.

The engineering process of specifying a CT string’s taper profile — O.D., wall thickness schedule, grade, and length distribution — to balance weight, pulling capacity, pressure rating, and fatigue life against the intended well profiles. Proper string design maximizes runs to retirement and overall string utilization.

The primary well control barrier in a CT stack, using energized elastomer elements to maintain a dynamic seal around the CT string as it moves in and out of the live wellbore, containing well pressure and fluids during intervention.

A CT string manufactured with multiple wall thicknesses along its length — heavier wall in high-stress and high-fatigue sections (typically the surface end and gooseneck cycling zones), lighter wall toward the downhole end — to optimize the trade-off between string weight, pulling capacity, and reach.

The measured or true vertical depth from surface datum to the deepest point of the wellbore.

A full-circumference girth weld (typically orbital TIG) joining two sections of finished coiled tubing, used for string repair or splicing. Tube-to-tube welds carry a significant fatigue-life derating relative to parent pipe and are individually tracked in string fatigue management.

Pre-job engineering modeling of axial loads, drag, buckling onset, and lockup depth for a CT string in a specific well trajectory, incorporating friction coefficients, residual bend, fluid effects, and WOB requirements. TFA establishes reach feasibility, weak-point loads, and safe operating envelopes before mobilization.

A gas tungsten arc welding (GTAW) process using a non-consumable tungsten electrode under inert shielding gas. Used for high-integrity welds, including tube-to-tube (butt) welds in coiled tubing manufacture and repair.

A non-destructive inspection method using ultrasonic pulse-echo to measure remaining wall thickness of the CT string, monitoring wall loss from wear, corrosion, or ballooning against minimum wall retirement criteria.

The relationship between wellbore hydrostatic (plus applied) pressure and formation pore pressure. Underbalanced conditions (wellbore < formation) invite influx and require live-well pressure control; overbalanced conditions (wellbore > formation) risk fluid losses and formation damage. CT operations are routinely designed to run in either regime.

The radial distance between the inside diameter (I.D.) and outside diameter (O.D.) of the pipe body. A governing parameter for burst, collapse, tensile ratings, and fatigue life.

The load-measurement system at the injector head displaying string weight (tension) or snub force (compression) at surface in real time. Weight trends are the operator’s primary indication of drag, hole condition, tagging fill, sticking, and approach to overpull or buckling limits.

The surface pressure-containing equipment installed at the top of the well, providing casing and tubing hanger support, annular access, and the interface for the production tree and intervention pressure control stack.

The shut-in or flowing pressure measured at the wellhead. WHP determines pressure control equipment ratings, stripper energization, snub force requirements, and the pipe-light/pipe-heavy balance for a given CT size.

Any operation performed on a producing or shut-in oil or gas well across its life cycle — stimulation, cleanout, logging, fishing, milling, remediation, or abandonment — to restore, enhance, or evaluate well performance and integrity.

Intervention conveyance using electric line or slickline lowered into the wellbore under gravity to perform operations such as logging, perforating, and setting or pulling plugs and downhole flow control devices.

The stress at which pipe material transitions from elastic to permanent (plastic) deformation, specified as a minimum per CT grade. Yield strength underpins all pressure, tension, and collapse ratings, though CT is unique among oilfield tubulars in being routinely and intentionally worked beyond yield during every bending cycle.