Casing Inspection Log in WCSB Well Integrity Programs: Electromagnetic Flux Leakage, Multi-Finger Caliper, Ultrasonic Casing Inspection, Corrosion Detection, and AER Directive 009 Abandonment Assessment for Aging Cardium, Viking, and Lloydminster Producers

Key Takeaways

• Electromagnetic flux leakage (MFL) casing inspection tools for WCSB corrosion assessment including the tool operating principle, magnetizing assembly, detector array configuration, and the distinction between internal corrosion (pitting in the casing ID from wellbore fluids) and external corrosion (galvanic attack on the casing OD from formation waters and stray electrical currents) in aging Cardium and Viking vertical producers: Electromagnetic flux leakage tools saturate the casing wall magnetically, then detect flux density with Hall-effect sensors in a circumferential array. Wall thickness reductions (corrosion pits, perforations, cracks) force flux lines to leak around the defect, producing a detectable anomaly whose amplitude is proportional to wall loss. MFL tools detect both internal and external wall defects because the magnetic field penetrates the full wall thickness (17-23 mm for standard WCSB 5-1/2 inch production casing) and senses defects from either surface. Internal corrosion pitting results from CO2 and H2S creating carbonic acid attack on uncoated casing surfaces; external corrosion comes from formation water in cement-void sections, trapped mud oxygen, or stray pipeline currents. Legacy WCSB Cardium and Viking producers drilled before 1980 frequently show 1-3 mm external wall loss at cement-void sections over 30-50 years.
• Multi-finger caliper (MFC) casing inspection for WCSB well integrity assessment including the tool configuration, feeler-arm sensor design, and the interpretation of inside diameter profiles to identify deformation, scale deposits, collapsed sections, and perforation damage in Lloydminster and Viking production casing strings: The multi-finger mechanical caliper uses a radial array of spring-loaded feeler arms (18, 24, or 40 arms depending on the WCSB tool size and required resolution) that extend to contact the casing inside surface and record the radial displacement of each arm as the tool moves through the wellbore at 2-5 m/min. The 40-arm high-resolution MFC produces a 360-degree image of the casing ID with 9-degree angular resolution per arm, sufficient to resolve individual perforation entries (typically 10-12 mm diameter in 4-1/2 inch guns) as isolated ID enlargements at the perforated interval. MFC logs in WCSB production casing programs identify: ovality (non-circular casing cross-section from formation squeeze load, typically found where WCSB Cretaceous shale creep has collapsed the casing in old vertical wells); internal scale deposits (carbonate or iron sulfide scale appearing as uniform or patchy ID reduction of 2-10 mm below nominal in Lloydminster heavy oil producers where steam or CO2 production creates scale); perforation tunnel collapse (perforations that have partially closed from formation sand production or scale infilling, visible as reduced radius at perforation depth); and casing split or buckle (a catastrophic ID deformation from external collapse load, where one or more arms indicate a local ID reduction of 20-50 mm, identifying a section that must be milled before abandonment). MFC logs are typically combined with MFL logs in the same tool string for a comprehensive WCSB casing integrity survey run in one wireline trip.
• Ultrasonic casing inspection for WCSB high-accuracy wall thickness mapping in deep Montney and Devonian sour gas wells including the pulse-echo measurement principle, omnidirectional transducer configuration, and the advantages of ultrasonic measurement over electromagnetic methods for precise quantification of wall loss in H2S-corrosive service environments: Ultrasonic tools emit short (100-500 ns), high-frequency (500 kHz to 2 MHz) acoustic pulses from an omnidirectional piezoelectric transducer through wellbore fluid to the casing wall, receiving echoes from the ID and OD surfaces. Wall thickness = (time between ID and OD echoes) × 5,900 m/s / 2. Ultrasonic tools achieve wall thickness resolution of 0.1-0.3 mm (versus MFL resolution of approximately 1 mm), enabling detection of early-stage corrosion pitting before it progresses to the level detectable by MFL methods. For WCSB Foothills Devonian sour gas wells with H2S partial pressures above 0.5 MPa, where L-80 production casing is exposed to corrosive brine at 120-140 degrees C reservoir temperature, ultrasonic casing surveys are performed every 3-5 years as part of the AER Directive 009 integrity monitoring program to detect corrosion growth rate before wall thickness approaches the minimum acceptable level. A limitation: gas-filled or heavy oil wellbores produce poor ultrasonic signal quality; WCSB operators fill the wellbore with water or brine before running the tool in gas producers.
• Casing inspection log interpretation standards for WCSB well integrity and abandonment decisions including the minimum remaining wall thickness criterion, the pitting density threshold for condemning a casing section, and the AER regulatory framework for well suspension or remediation when casing inspection results fall below the minimum integrity threshold under AER Directive 009: The 80% wall criterion: if measured wall thickness falls below 80% of nominal, the section is deficient and must be remediated or the well suspended. For 5-1/2 inch, 17 lb/ft casing (nominal wall 7.72 mm): minimum acceptable is 6.18 mm; measurements below this threshold trigger a Directive 009 integrity concern requiring AER notification. For perforated intervals, the ID enlargement from perforation tunnels is expected; inspectors distinguish perforations (localized, angular enlargements at known completion depths) from corrosion pitting (random, smooth-edged enlargements between perforated intervals). AER Directive 009 specifies that wells with confirmed casing wall defects below the minimum threshold must be remediated (casing patch installed, cement squeeze to externally support the thinned section, or section milling) or suspended under Directive 020 pending abandonment, with the remediation plan approved by AER before returning the well to production service.
• Pre-abandonment casing inspection log program for WCSB Cardium and Viking vertical well abandonment under AER Directive 020, including the inspection scope required to confirm casing integrity for isolation plug placement, the use of inspection results to determine whether casing perforation and squeeze or mechanical perforation is needed to achieve zonal isolation, and the typical findings in 40-60 year old WCSB producers: AER Directive 020 (Well Abandonment) requires that the operator verify casing integrity across all planned abandonment isolation plug intervals before proceeding with abandonment. For WCSB vintage producers drilled 1955-1980, a combined MFL-MFC survey runs from wellhead to total depth to identify: sections with significant wall loss (needing squeeze before plug placement); casing collapse or ovality (requiring section milling); perforated intervals needing bridge plug plus cement isolation; and sections with insufficient remaining wall for abandonment plug integrity. Thirty to fifty percent of production casing in 50-year-old WCSB wells fails the 80% wall criterion, typically at the base of surface casing (oxygen-rich groundwater attack at cement-void sections) and at perforated intervals (CO2 and water carbonic acid attack). Typical remediation includes external squeeze cementing at thinned sections and a mechanical casing patch at severely corroded sections before the final abandonment plug is set.