collar lock

A collar lock (also called a casing collar locator lock, CCL lock, or tubing stop) is a downhole mechanical anchoring device used in wireline and coiled tubing operations to secure a tool assembly at a specific casing or tubing collar by engaging spring-loaded or hydraulically actuated locking dogs that extend radially into the recessed groove of the coupling, preventing upward or downward axial movement of the tool string during operations that generate large transient forces — including perforating gun detonation (producing axial impulse loads of 5 to 30 kN), plug setting (requiring 10 to 50 kN set-down force on the plug element), and packer inflation (requiring sustained weight application) — that would shift an unanchored assembly from its target depth and displace charges or tools into the wrong formation interval. The collar lock works in conjunction with a casing collar locator (CCL) sensor that confirms the tool is positioned at the correct collar, identified by counting CCL spikes from a known reference depth (the casing shoe or liner top) against the casing running tally, before the locking dogs are actuated; this CCL-confirmed position is mechanically fixed by the collar lock at a depth accuracy of 0.1 to 0.5 m, independent of cable stretch or CT encoder errors that grow with depth and are the dominant source of perforation depth uncertainty in deep WCSB wells. In the Western Canada Sedimentary Basin, collar locks are deployed across the range of cased-hole completion and intervention operations: in WCSB Devonian reef recompletions at Pembina, Swan Hills, and Bonnie Glen, wireline-conveyed collar locks with integrated CCL subs position perforating guns at specific Devonian carbonate intervals identified 2 to 5 m above or below a known collar to access bypassed reef pay zones in 5 to 18 percent porosity carbonates without perforating adjacent water-bearing intervals; in WCSB Montney and Duvernay horizontal plug-and-perf operations at 2,000 to 4,000 m measured depth, CT-conveyed collar locks integrated in the plug-setting BHA confirm that composite frac plugs are being set at the designed stage boundary before the setting charge is fired; and in WCSB Mannville heavy oil recompletions using through-tubing CT operations at Lloydminster and Cold Lake, collar locks anchored in the production tubing coupling allow through-tubing perforating guns to be fired with the impulse load carried by the collar rather than by the CT string in compression, preventing the CT string from buckling downhole during the perforating shock event.

• Spring-set versus hydraulic-set collar lock actuation mechanisms and WCSB application selection: Spring-set collar locks deploy their locking dogs passively as the tool string is lowered through a collar and then pulled upward; the dogs are held retracted against spring tension by a sleeve that releases when the tool enters the collar recess, allowing the dogs to snap outward and engage the collar ledge as the tool is pulled back up through the recess. Spring-set designs require no surface actuation signal and are the standard for wireline-conveyed perforating systems in WCSB Devonian and Cretaceous cased-hole operations where the tool string moves continuously downward during deployment and the dogs set automatically when the correct collar is reached during the upward positioning move. Hydraulic-set collar locks extend the locking dogs when tubing pressure (typically 3 to 10 MPa applied through the CT or wireline cable pump-down system) is applied at surface, providing positive confirmation via a surface pressure response that the dogs have engaged the collar recess; hydraulic-set designs are preferred for CT-conveyed operations in WCSB Montney horizontal wells where the CT can apply downward force to confirm dog engagement against the collar ledge, and for high-load applications such as WCSB HPHT recompletions where the perforating impulse force (up to 30 kN for large-caliber HMX gun charges in 5-1/2" casing) requires the full hydraulic-set dog preload to prevent slippage.
• J-slot, overpull, and shear-pin release mechanisms for collar locks in WCSB wireline and CT operations: Once a collar lock is set, retrieving the tool requires intentional release of the locking dogs from the collar recess; three release mechanisms are used in WCSB operations depending on the tool configuration and operational constraints. J-slot release mechanisms (standard for rotatable wireline tool strings) require a specific sequence of upward tension and right-hand or left-hand rotation (typically 1/4 to 1/2 turn) that cams the J-pin out of its locking position and retracts the dogs, allowing the tool string to be retrieved; J-slot release is reliable in vertical and deviated wells where cable torque can be transmitted to the tool but is impractical for CT-conveyed collar locks in horizontal wells where CT torsional transmission is limited by friction. Overpull release mechanisms disengage the dogs when a threshold tension (typically 30 to 80 kN above string weight) is applied from surface, shearing a retaining ring or compressing a release spring, allowing retrieval without rotation; overpull release is standard for CT collar locks in WCSB Montney horizontal wells where the CT cannot transmit torque but can apply tension by reeling in at the injector. Shear-pin release (sacrificial release) allows the tool to separate from the collar engagement if overpull exceeds a predetermined force, used as a backup release mechanism in stuck-tool scenarios to recover the wireline or CT string without a fishing operation.
• Depth accuracy advantage of collar lock positioning over cable-only depth measurement in WCSB deep cased-hole operations: Wireline cable-measured depth in WCSB wells accumulates errors from three sources that collar lock positioning eliminates: cable elastic stretch under its own weight and tool string weight (standard 7/32" slickline stretches approximately 0.003 percent per meter, yielding 0.09 m at 3,000 m depth, which is small but compounding with other errors); cable temperature elongation as the cable heats from surface to wellbore temperature (WCSB Devonian reef wells at 60 to 80 degrees Celsius bottomhole temperature cause 0.1 to 0.3 m of additional cable length at 3,000 m); and sheave wheel calibration errors at the wellsite measuring block (typically plus or minus 0.05 to 0.15 m per 1,000 m). Combined, these errors produce absolute depth uncertainty of 0.2 to 0.6 m at 3,000 m for carefully corrected cable measurements, growing to 0.5 to 1.5 m for field operations without temperature or stretch corrections. Collar lock positioning reduces this to 0.1 to 0.3 m — the uncertainty in collar tally depth from the running record — which is sufficient to place WCSB perforating charges within 0.5 m of the designed top perforation in a 3 to 5 m target interval.
• Premium connection and liner completion compatibility issues for collar locks in WCSB HPHT and extended-reach wells: Standard API round-thread and buttress-thread coupling collars have a well-defined internal recess (0.5 to 1.5 mm step between the coupling ID and the pipe body ID) that collar lock dogs engage reliably; premium threaded connections (VAM TOP, Tenaris Blue, TenarisHydra, JFELION) used in WCSB Foothills HPHT wells and extended-reach horizontal wells have modified coupling profiles with flush or near-flush internal geometry, a smaller or asymmetric coupling recess, or a beveled transition that reduces the mechanical ledge available for dog engagement. Before deploying a collar lock in a WCSB Foothills well with premium connections (common in 7" production casing at 3,000 to 6,000 m depth in Nikanassin, Cadomin, or Devonian reef targets), the wireline or CT engineer must confirm the connection's internal coupling geometry with the casing manufacturer and select a collar lock dog profile sized and radiused for that specific coupling's shoulder height and recess depth; using a standard API dog profile in a premium connection can result in partial or no engagement, and the subsequent perforating shock may dislodge the tool entirely.
• Collar lock deployment in WCSB through-tubing recompletion programs using CT-conveyed perforating guns: Through-tubing recompletions in WCSB Devonian and Cretaceous cased-hole wells use CT-conveyed collar locks to anchor through-tubing perforating gun assemblies within the production tubing string while firing charges through the tubing wall into the formation; the collar lock must engage the tubing coupling rather than the casing coupling, requiring a tool OD sized for the tubing ID (typically 44 to 60 mm OD collar lock for 73 mm or 89 mm production tubing) and a dog profile matched to the tubing coupling recess geometry, which differs from casing coupling profiles. In WCSB Mannville heavy oil through-tubing recompletions at Lloydminster and Pelican Lake, where 73 mm tubing at 1,200 to 1,800 m depth is used with 44 mm CT-conveyed guns, the collar lock anchored in a tubing coupling transfers the 8 to 15 kN perforating impulse load to the tubing coupling ledge rather than allowing the CT string to recoil uphole during the shot; without the collar lock, CT recoil in the 200 to 500 m horizontal section of these deviated wells shifts the gun assembly 0.3 to 0.8 m during detonation, distributing some perforations outside the target interval and reducing zonal coverage by a full perforation cluster spacing.

WCSB Devonian Reef Recompletion Using Collar Lock Depth Control

A Pembina field operator used a wireline-conveyed collar lock with integrated GR-CCL sub to perforate a bypassed Nisku D reef interval at 2,340 m depth, 3.2 m below collar 58 from the 7" casing shoe, in a 1987-vintage producer that had only perforated the Nisku A interval. The CCL confirmed collar 58 position against the casing tally, the spring-set collar lock engaged the collar recess, and the gun string was positioned 3.2 m below the lock using a calibrated spacer sub. The 4-1/2" through-tubing HMX gun fired 4 shots per metre across an 8 m interval at reservoir depth. Post-perforation pressure buildup confirmed 14 percent porosity carbonate at 22 MPa initial pressure, adding 45 bbl/d oil at a recompletion cost of $180,000 versus $2.8 million for a new well targeting the same interval on a tighter offset location. The collar lock's 0.2 m absolute positioning accuracy was critical: a 1-collar error (2.3 m) would have perforated tight anhydrite above the reef crest with no productive interval.

Related Terms

Collar locator (CCL) is the companion sensor that confirms the tool is at the correct collar before the lock is set; the CCL spike count from the casing shoe against the running tally establishes the verified collar position that the collar lock then mechanically fixes in WCSB cased-hole operations. Perforating gun generates the axial impulse load that the collar lock resists; without anchoring at the target collar, gun recoil during detonation can shift WCSB perforation clusters 0.3-0.8 m from their designed position in the target formation. Coiled tubing conveys collar locks in WCSB Montney plug-and-perf and through-tubing recompletion operations; hydraulic-set collar locks are preferred because CT cannot transmit the rotation required by J-slot release in horizontal wellbores. Bridge plug setting requires collar lock anchoring in WCSB multi-zone completions; the plug setting force (10-50 kN) must be reacted against the collar ledge rather than the CT string in compression to prevent CT buckling in long horizontal sections at 2,000-4,000 m measured depth. Wireline deploys spring-set collar locks in WCSB Devonian and Cretaceous cased-hole perforating; J-slot release allows the wireline tool string to be retrieved after perforating without a separate fishing trip.