Casing Hanger in WCSB Wellhead Design: Slip-Type and Mandrel Hanger Configuration, API 6A Specification, Wellhead Pressure Seals, Installation Under Pressure, and Casing Head Stack Architecture for Cardium, Viking, and Montney Wells

Key Takeaways

• Slip-type casing hanger design and installation procedure for WCSB surface and intermediate casing strings including the slip segment configuration, setting mechanism, load transfer path from casing string to casing head bowl, and the wellbore pressure sealing function of the elastomeric or metal seal element: The slip-type casing hanger (the most common WCSB wellhead configuration for surface and intermediate casing) uses a conical bowl profile machined into the casing head bore that receives a set of segmented steel slips (typically 3-4 segments) with serrated teeth on the inside surface that bite into the casing OD and wedge-lock as the casing string weight drives the slips down the conical bowl taper. The slip locking is self-energizing: the heavier the casing string weight, the harder the slips grip the pipe OD, providing reliable load transfer for casing strings from 50 to 5,000 kN (limited by the casing OD crush strength rather than the hanger capacity). Installation: after the shoe reaches landing depth, the casing is pulled up 5-15 kN (overpull ensures slips engage under tension rather than compression), the slips are set with a slipping tool, and string weight is transferred to the hanger. After slipping, an elastomeric or metal-to-metal seal above the slips seals the hanger OD to the casing head bore against annular gas migration. AER requires pressure testing the hanger to rated working pressure after installation.
• Mandrel-type casing hanger design for WCSB production casing in high-pressure Montney and Duvernay wells, including the seal bore configuration, metal-to-metal wellhead seal, installation under wellbore pressure with a BOP stack in place, and the advantages of the mandrel hanger over slip hangers for gas-tight wellhead applications: The mandrel casing hanger (also called a premium hanger or gas-tight hanger) uses a machined cylindrical mandrel with a polished OD that lands on a machined shoulder inside the casing head, transferring casing string weight through the mandrel body to the shoulder rather than through teeth biting into the casing OD. The mandrel hanger provides an undamaged casing OD and a polished seal surface accepting an API 11D1 isolation seal between the hanger mandrel OD and the casing head bore. For WCSB Montney and Duvernay production casing programs where wellhead working pressure exceeds 35 MPa (5,000 psi), mandrel hangers with metal-to-metal seals (capable of 70-100 MPa seal pressure) are preferred over slip hangers with elastomeric seals (typically rated 35-55 MPa). Installation in WCSB high-pressure wells requires a BOP on the intermediate casing head: the hanger is made up to the casing top, run through the BOP, and landed under positive wellbore pressure with blind rams closed; the BOP is then removed and the tubing head attached. This live-well procedure is standard for WCSB Montney wells where kill fluid would damage the reservoir.
• Casing head and wellhead stack architecture for WCSB multi-string well programs, including the bolted flange connections between casing head spools, the conductor casing head that forms the structural base, and the load path from production casing hanger through intermediate and surface casing heads to the conductor casing cemented in the formation: A WCSB horizontal well with a four-string program builds a wellhead stack from bottom to top: conductor casing head (welded to conductor casing, set in grout or driven); surface casing head (houses surface casing slip hanger, isolates conductor-surface annulus); intermediate casing head (houses intermediate casing hanger, isolates surface-intermediate annulus); and production casing head (houses production casing hanger, isolates intermediate-production annulus). The tubing head or wellhead christmas tree is then bolted to the production casing head for production. The full stack height for a WCSB Montney horizontal well is typically 1.2-2.0 m above the wellpad surface, with each casing head spool contributing 200-400 mm of height. All bolted flanges use API 6A ring-type joint (RTJ) gaskets or spiral-wound gaskets (for lower-pressure applications) to provide the gas-tight flange connection required by AER Directive 036 for WCSB wellhead assemblies.
• Casing hanger annular seal selection and pressure testing for WCSB wellhead gas isolation requirements under AER Directive 036, including the distinction between the hanger pack-off seal that isolates the casing-to-casing annulus and the wellhead isolation valve required for sour gas wells and wells above a specified wellhead pressure threshold: AER Directive 036 (Drilling Operations) specifies that WCSB wellheads must have pressure containment capability in the annular spaces between all concentric casing strings to prevent gas migration from a deeper pressured zone through the annulus to the surface. The casing hanger pack-off seal (the elastomeric or metal seal element above the slip or mandrel body) provides this isolation for the primary annulus; AER requires that the pack-off seal be pressure-tested to the higher of 50% of the minimum internal yield pressure of the smaller casing string or the anticipated wellbore pressure at the hanger, held for 10 minutes with less than 0.35 MPa decay. For WCSB sour gas wells (H2S above the AER Directive 036 threshold), additional requirements include a surface safety valve on the annulus outlet of the casing head, allowing remote closure of the annulus if surface casing vent flow develops. WCSB wellhead hanger seals are inspected at each scheduled rig workover visit and replaced at first indication of seal degradation (sustained annulus pressure above the AER Directive 009 threshold indicating a hanger seal leak rather than a formation communication path).
• Wellbore integrity and load verification for WCSB casing hangers including the hanger weight capacity check against the maximum string weight for deep Montney and Foothills casing programs, the stimulation-induced tension load at the hanger during multistage fracturing, and the hanger slip crush limit as the governing constraint for heavy casing strings in larger wellhead sizes: Casing hanger capacity verification for WCSB deep horizontal wells involves three separate load checks: static string weight (the buoyed weight of the full casing string hanging from the hanger in the wellbore fluid); stimulation tension load (the additional axial tension developed at the hanger from Poisson effect and thermal expansion changes during fracturing, which can add 5-15% to the static load for deep WCSB Montney wells at 70-80 MPa fracturing pressure); and the maximum slip crush load (the radial compressive force that the slip teeth generate on the casing OD, limited by the casing body's API 5CT specified minimum collapse strength). For 5-1/2 inch, 17 lb/ft, L-80 production casing on a 200-joint lateral (2,700 m of pipe): static buoyed weight in 1.1 specific gravity cement = approximately 350 kN; stimulation tension at 75 MPa wellhead pressure adds approximately 50 kN (Poisson ratio 0.28, steel area of pipe body 23.5 cm2); total hanger load = 400 kN. A standard WCSB 5-1/2 inch slip hanger rated at 800 kN capacity provides a safety factor of 2.0 against the total load, adequate for standard Montney programs. For heavier casing strings or larger-OD casing, slip crush becomes limiting before hanger body capacity, requiring a larger casing head to provide a longer slip seating surface that distributes the radial load over more casing circumference.