Through-Tubing Ultrasonic Leak Detection Technology and Its Application in Gas Storage Wells

Gas storage wells are subjected to long-term cyclic loads, which can lead to wellbore leakage and sustained annular pressure across multiple barriers. Accurately identifying micro-leak locations and pathways in multi-string wellbores is critical for managing and mitigating complex annular pressure issues. Ultrasonic leak detection offers high sensitivity and precision, enabling the capture and localization of minor leaks. However, detecting leaks behind the tubing—such as in casings or cement—poses challenges, including rapid ultrasonic attenuation in multi-layered media, weak signal acquisition, and difficulties in effective signal processing. To address these challenges, research was conducted on weak ultrasonic signal acquisition methods, acoustic field distribution characteristics for behind-tubing detection, tool development, detection techniques, and field testing. Results show that a high-sensitivity gas-coupled ultrasonic receiver probe was developed with a maximum gain of 120 dB and baseline noise fluctuation controlled within 0.6%. The probe successfully captured ultrasonic signals from simulated leaks at different positions, clarifying signal intensity variations along the wellbore axis. Key hardware modules for the behind-tubing ultrasonic leak detection tool were developed, including an acoustic module, multi-parameter auxiliary module, and noise-reducing roller centralizers, suitable for tubing sizes ranging from 73 to 177.8 mm. Laboratory tests under simulated downhole conditions quantified temperature compensation coefficients and calibrated detectable leak rates, confirming a minimum detectable casing leak rate of 0.5 L/min behind tubing. A field test in a gas storage well successfully identified micro-leaks in the tubing and casing, as well as the upward migration path in the B-annulus, verifying the technology’s feasibility. This method shows promising potential for wellbore integrity evaluation in gas storage and high-pressure gas wells.