Comprehensive Diagnostics and Advanced Ultrasonic Technology for Managing Corrosion and Leak Risks in Sour Gas Well Configurations

Abstract A sour gas environment presents significant risks to producing wells due to the high levels of CO2 and H2S, which accelerate corrosion in well completions—especially at high production rates. In one case, a 12 MMscfd HPHT sour gas well developed sustained annulus pressure in the production casing, suspected to have been caused by a leak in its 22Cr-125 production tubing. Concerns were raised that the loss of the nitrogen cushion in the production annulus had allowed sour gas to accelerate external corrosion. With at least 20 other wells sharing similar configurations, the client faced the risk of widespread issues and began considering workovers as well as redesigning tubing and casing configurations for future wells. Multiple diagnostic technologies were used to locate the leak and assess the condition of the tubing. A conventional multifinger caliper log indicated that the internal condition of the tubing was good, with no significant wall penetration or leaks detected—yet the tubing leak persisted. An optical camera run was then performed, and the footage revealed several suspected spots along the tubing that appeared to be holes or pitting, raising further questions for the client about the actual condition of the tubing. To address the limitations of the multifinger caliper and optical camera, two ultrasound technologies were introduced: one based on passive acoustic listening, and the other a phased array ultrasound tubing-casing scanner. The passive acoustic listening tool features broad frequency coverage from 355 Hz to 656 kHz and a patented pressure-balanced insertion assembly, enabling it to detect a variety of leak types with high sensitivity—even those with low acoustic intensity or amplitude. Deployment of this tool successfully identified a tubing leak at a shallow depth above the downhole safety valve, providing the client with a conclusive result on the barrier failure. However, the precise internal and external condition of the tubing remained unclear. This case highlighted the limitations of the multifinger caliper tool, which requires constant physical contact with the tubing wall and is prone to missing small leaks due to the gaps between its fingers. Additionally, it is incapable of assessing the external condition of the tubing. To overcome these limitations, the phased array ultrasound tubing-casing scanner was deployed. This tool projects an acoustic beam to measure dimensions without requiring physical contact, calculating the internal diameter (ID) based on the speed of sound in the well fluid. Multiple ultrasonic transducers enable beamforming for high resolution and precise focus. The tool is equipped with 288 sensors arranged circumferentially at 1.25° spacing, each fitted with 3.3 MHz transducers in a phased array configuration. This allows for accurate measurement of both internal and external tubing dimensions, including complex profiles, without any moving parts. It provided highly accurate assessments of the tubing wall, measuring dimensions to within a hundredth of an inch. Both ultrasound technologies confirmed the tubing's overall good condition—aside from the in-situ leak—and reassured the operator about the integrity of the other wells. This enabled the operator to engineer targeted remediation for specific issues, de-risk the well, and avoid costly completion replacements. The case also demonstrated the effectiveness of advanced ultrasonic technology in assessing tubing integrity, not limited to sour gas environments, and offered a practical alternative to traditional tools by reducing risks and costs for wells with similar configurations.