Measuring and Profiling Casing Corrosion for Predicting Subsurface Leaks

Locating downhole casing leaks in producer and injector wells is not a complex undertaking when using rig-operated straddle packers with pressure testing. However, this established technique has limited effectiveness because it does not necessarily address the overall comprehensive integrity of the entire completion, which might include additional intervals of serious corrosion leading to leaks in the near future. We examined the results of low-frequency electromagnetic (EM) remote frequency eddy current (RFEC) wireline logs from over 80 wells in one mature Middle Eastern offshore field, profiling the severity of measured metal loss (ML) from concentric casings against proven rig-discovered leaks and rigless measurements of subsurface ML. Casing leaks that otherwise would have been detected only by conventional zonal pressure testing from a workover rig can now be located and forecasted with a high degree of probability when using this evaluation tool. The importance of maintaining oilfield casing integrity for safety, environmental, and flow assurance objectives, combined with the high costs of drilling new wells, creates a necessity for this integrated well integrity appraisal approach. Application of this EM logging technology to identify intervals of external ML has great significance in being able to anticipate casing intervals with high likelihood of failure due to invasive corrosion.