Project Background
In May 2022, abnormal gas logging was detected in a horizontal well of Southwest Oil & Gasfield after casing running and cementing in the fourth spud section, with the wellhead gas flow rate ranging from 0 to 92 m³/h, indicating a suspected casing collar leakage. The field operation faced multiple challenges: the high mud weight made it difficult for the distributed optical fiber monitoring system to capture micro-leakages; the high downhole pressure caused the failure of conventional sealing methods, and the surge pressure during cable lifting led to fiber optic breakage; reducing the mud weight introduced well control risks, and there was a lack of matched tubing inner cable suspension tools. In addition, the optical cable depth calibration method was inaccurate, making it impossible to effectively determine the causes and attenuation of suspected defect points on the optical fiber.
Our Solution
We adopted distributed optical fiber sensing technology, running the optical cable to a depth of 4500 meters through the drill string water course, and implemented combined monitoring of Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS). By using DAS frequency band analysis to identify downhole fluid flow signals and combining them with abnormal temperature changes, we achieved accurate positioning of the leakage points.
Final Results
We successfully determined the downhole leakage locations: there was annulus channeling in the interval of 3815–4415 meters, and accurately identified 4 casing leakage points including 3971.2 m and 4001.2 m, all corresponding to casing collar positions. The rapid and precise positioning of the leakage interval provided a reliable basis for subsequent repair operations.
Customer Evaluation
This technology effectively solved the problem of leakage and channeling detection under complex well conditions, demonstrating the reliability and accuracy of the distributed optical fiber monitoring system in high-temperature and high-pressure environments. It provided key technical support for the customer's subsequent wellbore integrity management and was highly recognized by the on-site technical team.
