Casing Gun in WCSB Completion Operations: Cased-Hole Perforating Gun Design, OD Clearance to Casing ID, Wireline and TCP Conveyance, Charge Selection, and Primary Completion Applications in Cardium, Viking, and Montney Wells

Key Takeaways

• Casing gun design and carrier tube configuration for WCSB primary completions including hollow-carrier, semi-expendable, and fully expendable designs, charge phasing patterns, and the selection of gun OD relative to the production casing ID for 5-1/2 inch and 7 inch WCSB completion programs: The standard WCSB casing gun design is the hollow-carrier system: shaped charges are loaded into threaded ports in a steel carrier tube, with each charge enclosed in a charge holder that positions the charge at the designed standoff from the casing wall and aligns the jet with the perforating phase angle. The carrier tube protects the charges from wellbore pressure until detonation and, after firing, contains the detonation debris (spent charge carrier, end disks, detonating cord fragments) within the gun body for retrieval at surface, leaving no gun debris in the wellbore. For 5-1/2 inch production casing (ID 4.670 inch for 17 lb/ft), a 3-3/8 inch OD carrier gun leaves 0.65 inch annular clearance, while a 4 inch OD gun leaves 0.34 inch clearance, with the larger gun providing more room for heavier charges but requiring tighter borehole quality to run without hang-up. Charge phasing for WCSB Montney plug-and-perf completions uses 60-degree phasing (6 charges per revolution of the carrier) to distribute perforations around the casing circumference, minimize casing structural damage, and improve fracture initiation symmetry; for limited entry designs with 3-4 shots per cluster, 120-degree phasing concentrates shots in fewer planes to maximize per-perforation flow rate. Shot densities range from 4 shots per metre (widely spaced clusters) to 20 shots per metre (dense perforation intervals) depending on the completion strategy.
• Wireline-conveyed casing gun operations in WCSB Cardium and Viking vertical completions including gun loading, surface assembly, wellhead lubricator deployment, depth positioning by CCL collar correlation, and the underbalance perforation technique for minimizing perforation skin in moderate-permeability sandstone targets: Wireline-conveyed casing gun operations in WCSB vertical well primary completions follow a standard sequence: the gun system (CCL sensor, gamma ray tool, firing head, and loaded gun sections) is assembled at surface in the wireline unit, hydraulically tested to the maximum wellbore pressure expected, and run in through the wellhead lubricator sealed against wellhead pressure. The tool string descends through the casing bore under gravity (possible only in vertical and low-deviation wells; in deviated or horizontal wells, the gun must be pumped or CT-conveyed), with the CCL log recording collar positions as the gun runs to depth. At the target depth (confirmed by CCL-tally pattern match within one collar), the gun is stationary while the CCL logs for depth confirmation, then fired electrically through the wireline cable. For WCSB Cardium primary completions (formation permeability 1-10 mD), underbalance perforation (wellbore pressure below reservoir pressure at the moment of detonation, typically 500-2,000 kPa) is used to create an immediate surge of reservoir fluid through the fresh perforations, flushing the crushed compacted zone and formation fines from the perforation tunnels before they can consolidate into a plugging skin. AER Directive 036 requires a wellhead lubricator assembly rated for wellbore pressure and an exclusion zone during firing.
• Tubing-conveyed perforating (TCP) system for WCSB horizontal Montney and Duvernay casing gun operations where wireline cannot push the gun to total depth in the horizontal lateral and the gun must be run on the tubing string, positioned by circulating and correlation, and fired by drop bar or pressure actuation at the surface: In WCSB Montney and Duvernay horizontal completions where the lateral length (1,500-3,500 m) prevents wireline-conveyed guns from reaching total depth (wireline cable cannot be pushed horizontally against friction), tubing-conveyed perforating (TCP) uses the production tubing string itself as the gun conveyance vehicle. The casing gun string (which may contain 50-200 individual gun sections plus packer assembly, firing head, and CCL tool) is made up at the bottom of the tubing string and lowered into the wellbore as a single assembly during the tubing running operation. After the tubing packer is set and depth is confirmed by CCL-tally correlation (using a memory CCL tool that records collar signals as the TCP string is run in), the gun is fired by drop bar (a weighted bar free-falls through the tubing and impacts the firing head), hydraulic pressure actuation (surface tubing pressure triggers the hydraulic head), or a wireline-run electrical detonator. TCP systems allow gun string lengths of hundreds of metres (the entire completion zone can be perforated in one run for single-zone completions), eliminating multiple wireline trips in wells where each trip requires hours of rig time for wellbore preparation.
• Charge selection and perforation geometry optimization for WCSB casing gun programs in tight rock Montney and Cardium completions scheduled for hydraulic fracturing, including the trade-off between deep penetration for tight rock and big-hole charges for fracture initiation, and the role of limited entry perforation design in controlling fracture distribution across multiple clusters per stage: Casing gun charge selection balances two objectives: deep penetration (DP) charges maximize tunnel length (500-700 mm in API RP 19B tests) at the cost of smaller entry hole diameter (12-13 mm), providing the deepest near-wellbore bypass but a narrower flow path; big-hole (BH) charges sacrifice penetration (300-400 mm) for larger entry holes (16-20 mm), enabling higher injection rates and more uniform fluid distribution among clusters. WCSB limited entry designs favor smaller-diameter, high-friction charges that maintain perforation friction at the designed injection rate to distribute fluid evenly among all clusters. Current WCSB Montney practice uses 3-5 shots per cluster with 0.3-0.5 inch (7.6-12.7 mm) entry holes at 60-degree phasing to maintain 1-3 MPa entry friction per cluster at typical pumping rates of 10-14 m3/min.
• Post-firing casing gun retrieval, misfired shot handling, and perforated interval quality verification in WCSB completion operations including post-job CCL confirmation, impression block survey to confirm perforation depth, and the AER Directive 065 reporting requirements for documented perforations in WCSB production and injection wells: After firing, a wireline-conveyed casing gun is retrieved to surface (for recovery type guns) or remains in the wellbore (for expendable type) before production tubing is run. Recovery of the gun at surface allows inspection for detonation completeness: all charge ports should show clearly blown-out profiles with no intact charge remaining; a port that shows no evidence of detonation is a dud requiring misfire handling under the Canadian Explosives Act (minimum 30-minute wait before approaching, then controlled neutralization or safe retrieval). WCSB completion engineers verify perforation depth and quality using two methods: a post-shot CCL log (a wireline run immediately after gun retrieval, before running tubing) confirms that collar-referenced depth of the perforated interval matches the intended target depth, as the perforations themselves do not change the CCL signal but any collar displacement during shooting would be detectable; and an impression block survey (a lead impression block run on coiled tubing and pressed against the casing wall at the perforated interval) creates a physical record of the perforation pattern (shot density, phasing, hole geometry) that can be compared to the gun specifications. AER Directive 065 requires that the measured depths of all perforations be documented in the well completion report and submitted within 30 days of completion.