coiled tubing completion

Coiled tubing completion is a well completion technique in which a continuous coiled tubing string serves as the primary mechanical delivery system for perforation guns, frac plug assemblies, velocity string installations, or through-tubing stimulation tools, allowing wells to be completed, re-completed, or optimized without the threaded-connection make-and-break cycle of conventional jointed workstring and without killing the well or pulling the existing completion string; the method is distinguished from general CT well intervention by its role in permanently altering the well's completion architecture (through new perforations, zonal isolation, or velocity string installation) rather than providing a temporary service that leaves the wellbore in its original configuration. In the Western Canada Sedimentary Basin, coiled tubing completions have become the dominant execution method for multistage hydraulic fracture programs in Montney siltstone, Duvernay shale, and Falher/Wilrich tight gas horizontal wells in northwest Alberta and northeast British Columbia, where operators including Tourmaline Oil Corp, Peyto Exploration and Development, Canadian Natural Resources, ARC Resources, and Ovintiv run CT plug-and-perf sequences across 20 to 60 stages per well, setting ball-drop or pump-down activated composite frac plugs at 60 to 100 m stage spacing and firing cluster-based perforating guns (4 to 6 clusters per stage, each cluster 0.3 to 0.5 m long with 6 to 12 shots at 60-degree phasing) to create the entry points for hydraulic fracture initiation; WCSB Montney CT plug-and-perf cycle time averages 2 to 4 hours per stage from plug set to perforations fired and guns retrieved, compared to 6 to 12 hours for jointed workstring alternatives, directly compressing the completion schedule and reducing the daily operating cost borne by the well. Beyond the unconventional play application, WCSB CT completions are used in three additional contexts: velocity string installations in liquid-loaded Cardium, Viking, and Mannville gas wells (32 to 38 mm CT string run inside 73 to 89 mm production tubing to concentrate gas velocity above the Turner critical rate and extend economic life by 2 to 5 years); through-tubing re-completions in mature Devonian and Cretaceous producers (CT-conveyed perforating guns and acid stimulation tools accessing bypassed pay zones above or below the existing completion without pulling the wellbore equipment); and observation well completions in WCSB Athabasca SAGD pads (CT-conveyed fiber-optic and thermocouple strings anchored in place to provide temperature profiles across the SAGD steam chamber for reservoir management).

• CT plug-and-perf mechanics, plug types, and perforation design in WCSB Montney and Duvernay completions: The CT plug-and-perf sequence begins with the CT string conveying a composite or degradable frac plug and perforating gun assembly to the target depth using depth correlation from the CT encoder wheel matched to gamma-ray log signatures (formation marker matching accuracy of plus or minus 1 to 2 m), setting the frac plug by dropping a ball down the CT or applying hydraulic pressure to shear a setting pin, then pumping the guns uphole to the next perforation cluster interval and firing by wireline or hydraulic signal. WCSB Montney plug-and-perf uses composite frac plugs (manufactured from glass-fiber reinforced plastic and magnesium alloy with 75 to 90 mm ball seat IDs rated to 70 to 85 MPa burst and 60 to 70 MPa differential pressure) that can be drilled out by CT-conveyed PDC mills at 15 to 45 minutes per plug after all stages are fractured, adding 12 to 48 hours of CT drill-out time per well for 20 to 60 plugs; degradable or dissolvable plugs made from high-strength magnesium alloys dissolve in produced fluids at 60 to 90 degrees Celsius within 30 to 90 days of fracturing, eliminating the drill-out requirement at a plug cost premium of $800 to $2,000 per plug versus $300 to $800 for composite, a trade-off that WCSB operators evaluate based on rig availability and the value of accelerating first production.
• CT velocity string completions for liquid-loaded WCSB gas wells: Velocity string CT completions are permanent installations designed to extend the economic producing life of WCSB Cardium, Viking, Mannville, and Nikanassin gas wells experiencing liquid loading once gas rates decline below the Turner critical velocity (the minimum gas flow rate needed to continuously lift produced water and condensate droplets to surface, proportional to tubing ID and wellbore pressure). A 32 mm (1-1/4") or 38 mm (1-1/2") CT string is pressure-pumped or mechanically pushed to total depth inside the existing 73 mm (2-7/8") or 89 mm (3-1/2") production tubing, sealed at the bottom with a velocity string anchor packer that directs gas flow up the CT-tubing annulus at increased velocity, and the CT tail is terminated above the existing packer to prevent recirculation of produced liquids; WCSB Cardium and Viking gas operators in the Pembina, Crossfield, and Brazeau areas install CT velocity strings at well capital costs of $50,000 to $150,000 per installation using a CT unit rigged up on the live well in 2 to 4 hours, typically extending the economic producing life of affected wells by 2 to 5 years without requiring compression or artificial lift equipment that would cost $300,000 to $800,000 per well to install and $50,000 to $100,000 per year to maintain.
• Through-tubing CT re-completions in WCSB mature Devonian and Cretaceous pools: Through-tubing CT re-completion is a well optimization technique in which a CT string is snubbed into a live producing well through the existing production tubing string (without killing the well or pulling the tubing) to access additional pay zones above or below the current completion interval and perforate them with CT-conveyed through-tubing perforating guns. WCSB Devonian carbonate pool operators in the Pembina, Swan Hills, Redwater, and Bonnie Glen fields use through-tubing CT perforating to access additional Devonian reef intervals or Mississippian carbonate zones at 1,500 to 3,500 m depth that were not completed during original drilling; the through-tubing CT gun OD must fit through the production tubing ID (a 73 mm 2-7/8" tubing with 62 mm ID limits the CT OD to approximately 44 mm and the through-tubing gun OD to approximately 38 mm), restricting perforation charge sizes to through-tubing HMX or RDX charges with penetration depths of 150 to 250 mm versus 400 to 600 mm for conventional full-bore guns, but still capable of creating productive perforations in WCSB Devonian carbonates with porosities of 5 to 18 percent. Post-perforation, acid stimulation is pumped through the CT to the new perforations (15 percent HCl acid for carbonate dissolving, 0.5 to 2 m3/min pumping rate, 5 to 20 m3 volume per zone), creating wormhole channels 0.5 to 2 m into the formation that add 50 to 500 barrels per day of production per zone at capital costs of $200,000 to $600,000 per re-completion versus $2 million to $5 million for a new vertical well.
• CT completion quality control, depth accuracy, and perforating depth correlation in WCSB horizontal wells: Depth accuracy is the critical quality control parameter in CT plug-and-perf completions because perforation cluster placement within 1 to 3 m of the designed interval boundary determines which natural fractures are intersected and whether hydraulic fractures initiate simultaneously from all clusters in the stage; WCSB CT operators use a multi-method depth correlation approach combining the CT encoder wheel (cumulative depth from the wellhead to within plus or minus 1 m accuracy over 3,000 m lateral), gamma-ray logs run on the CT immediately before plug setting to correlate the tool depth to formation markers visible on the original LWD log, and casing collar locator (CCL) signals from the CT-conveyed BHA that detect the electromagnetic signature of each casing collar at known spacing to provide an independent depth check. In WCSB Montney horizontal wells with natural gamma-ray contrast of 50 to 150 API units between siltstone (15 to 40 API) and shale interbeds (80 to 180 API), CT gamma-ray depth correlation accuracy is typically plus or minus 0.5 to 1.5 m, sufficient to place perforations within the target siltstone interval and avoid shale interbeds that would reduce fracture conductivity; WCSB operators specify a maximum depth mismatch of 3 m between the CT gamma-ray depth and the original LWD gamma-ray depth as an acceptance criterion for each plug-set operation before the hydraulic fracture treatment proceeds.
• CT completion cost benchmarking and economic comparison against wireline plug-and-perf in WCSB programs: CT plug-and-perf competes with wireline-conveyed plug-and-perf (where a wireline truck sets plugs and fires guns using electric line rather than CT) in WCSB Montney and Duvernay completions, with the economic advantage of each method depending on well depth, lateral length, stage count, and pumping schedule; wireline plug-and-perf has a lower mobilization cost ($15,000 to $25,000 for a wireline unit versus $35,000 to $60,000 for a CT unit in WCSB northeast British Columbia) but slower cycle time in horizontal wells because wireline conveyance requires pumping fluid at 1 to 3 bbl/min to push the assembly to toe in deviated wells, while CT can push with mechanical force from the injector head regardless of wellbore angle. WCSB operators have predominantly moved to CT plug-and-perf for Montney and Duvernay wells with more than 20 stages and laterals exceeding 1,500 m because the CT cycle time advantage accumulates to 1 to 3 days of saved completion time per well at $20,000 to $50,000 daily operating cost, generating $40,000 to $150,000 in completion cost savings per well that more than offsets the higher CT mobilization cost versus wireline for high-stage-count wells.

CT Velocity String Extending WCSB Viking Gas Well Economic Life

A WCSB operator managing a portfolio of 38 Viking Formation gas wells in central Alberta identified 12 wells experiencing liquid loading at gas rates of 15 to 40 Mcf/d with wellhead tubing pressures of 1.5 to 4 MPa, below the Turner critical velocity for the 73 mm production tubing installed in each well. A 32 mm CT velocity string program was designed to restore critical velocity by reducing the effective flow area. Each CT string was rigged up on the live well in 3 hours using a snubbing lubricator and pumped to total depth in 45 minutes, anchored with a velocity string packer at 850 m depth above the existing wellbore packer. Post-installation, all 12 wells showed continuous liquid lift restoration within 2 to 6 hours of installing the velocity string. Average gas rate per well increased from 18 Mcf/d (pre-installation, liquid-loaded) to 34 Mcf/d (post-installation, continuous flow), a 89 percent improvement. At a gas price of $3.20/Mcf, the program generated $145,000 in incremental annual revenue per well against an average installation cost of $85,000 per well, yielding a 7-month average payback across the 12-well program.

Related Terms

Coiled tubing is the technology platform for CT completions; the continuous unjointed steel string eliminates connection time and enables live-well entry without killing, making plug-and-perf and through-tubing re-completions 40-70% faster than jointed workstring methods. Plug-and-perf is the dominant WCSB Montney and Duvernay multistage completion methodology; CT conveys composite or dissolvable frac plugs and perforating gun strings to each stage interval in horizontal laterals of 1,500 to 3,000 m. Frac plug is the downhole isolation device set by CT between fracture stages; composite plugs are drilled out by CT after fracturing while dissolvable plugs degrade in produced fluids, eliminating the CT drill-out trip at a cost premium. Velocity string is the permanent CT installation inside larger production tubing that increases gas velocity above the Turner critical rate in liquid-loaded WCSB Cardium, Viking, and Mannville gas wells. Through-tubing perforation uses CT-conveyed gun strings to perforate new zones through existing production tubing in WCSB mature Devonian and Cretaceous wells without tubing pull, accessing bypassed pay at fraction of new-well cost.