Case: Gas Well Casing Leak Detection

Core Issue: Cementing Anomaly and Gas Channeling Risk
Field Situation: After casing cementing in the fourth spudding phase of Well Moxi XXX-H, gas logging anomalies were detected, with intermittent gas flow rates of 0–92 m³/h observed at the wellhead. This indicates a risk of gas migration from the formation to the wellhead through the casing annulus or the casing itself.
Initial Assessment: Based on engineering experience, the gas leakage path is likely related to casing collar seal failure, which compromises cement integrity and creates channeling pathways.

Technical Solution: Rapid Fiber Deployment and Dual-Parameter Monitoring
Operational Response: On May 12, 2022, fiber-optic cables were quickly deployed to a depth of 4,500 meters through the drill pipe conduit (inside the drill string), enabling one-time installation.
Monitoring Technology: Combined Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) systems were used for simultaneous monitoring, providing real-time temperature and acoustic vibration data across the entire wellbore.

Diagnostic Results: Precise Localization of Leaks and Channeling Sections
DAS Frequency Band Analysis: By analyzing acoustic energy characteristics across different frequencies, the following were identified,
Annular Channeling Section: Significant annular gas channeling signals were detected in the 3,815–4,415 meter interval (horizontal section), indicating cement seal failure and the formation of gas flow pathways.
Casing Leak Points: Four casing leak points were precisely located at depths of 3,971.2 meters, 4,001.2 meters, etc., all corresponding to casing collar positions, confirming collar seal failure.
DTS Supplementary Verification: Temperature data further revealed local anomalies caused by gas flow, corroborating the DAS findings.

Technical Value: Safety and Decision Support
Rapid Response: Deployment via the drill pipe conduit avoided complex casing trips, enabling diagnosis within hours and significantly shortening incident resolution time.
Precise Decision-Making: Results directly guided subsequent plugging or workover operations, clearly defining channeling sections for isolation and collars requiring repair or replacement.