High-Resolution Ultrasonic Casing Integrity Logging for Corrosion and Wall Loss Assessment

Abstract Casing corrosion is one of the primary threats to the long-term integrity of mature CoalBed Methane (CBM) wells. Accurate identification of metal loss and structural defects is essential for maintaining barrier integrity, optimising remediation strategies, and extending asset life. This paper presents the results of a large-scale ultrasonic Production casing integrity logging campaign conducted across 105 onshore CBM wells in Queensland, Australia. In many CSG wells, the production casing also functions as the primary conduit for produced water and gas. Consequently, deterioration of the casing is not solely a structural integrity concern but can directly affect production performance, zonal isolation, containment, and well longevity. Continuous exposure to produced fluids over the operating life of the well can result in localized corrosion and progressive wall loss, making reliable assessment of remaining casing thickness an important component of mature-well integrity management. A wireline-deployed, memory-based ultrasonic imaging tool was used to acquire high-resolution 360° casing images and quantitative wall-thickness measurements in 7-in. and 5.5-in. casing strings. Ultrasonic measurements were integrated with Gamma Ray (GR) and casing collar locator (CCL) data to improve depth correlation and defect localisation. Field acquisition procedures, quality-control workflows, calibration verification, and operational practices were developed to ensure reliable data acquisition under memory logging conditions. The surveys successfully identified a wide range of casing integrity conditions, including internal and external corrosion, uniform wall thinning, localized pitting, and isolated through-wall defects. The combination of ultrasonic travel time and amplitude measurements enabled accurate wall-thickness evaluation and differentiation between internal and external metal loss. The inspection results supported risk-based well integrity assessment, remediation planning, and long-term asset management across the surveyed field.