Deployment and Performance Evaluation of Bismuth Alloy-Based Thermally Deformable Annular Packer (TDAP) for Mitigating Gas Migration in Casing Annuli

Abstract Gas migration is a persistent challenge in oil and gas wells, affecting both newly drilled and mature wells. It poses significant risks, including compromised well integrity and the development of long, pressurized zones within the wellbore. The issue is particularly complex in offshore environments, where operational constraints and external conditions increase the difficulty of achieving effective zonal isolation. Despite the broad implementation of best practices in primary and remedial cementing, the industry continues to face recurring issues such as post-cementation gas flow, interzonal gas communication, and general cement sheath failure. Sustained casing pressure (SCP) events are particularly prevalent, with thousands of documented cases globally and continuing reports of well incidents related to SCP each year. These events can threaten both personnel safety and environmental compliance due to potential surface gas emissions and the risk of blowouts. A primary underlying cause of SCP is the existence of microchannels or larger pathways within the cement sheath located behind the casing. Such channels may arise from suboptimal cement placement practices, inadequate mud displacement, or mechanical and chemical debonding of the cement as a result of repeated thermal and pressure cycling during well operation. These defects compromise the long-term integrity of the annular seal and permit undesirable gas migration, even after careful design and quality control. To address this issue, a Thermally Deformable Annular Packer (TDAP) based on bismuth alloy can be incorporated into the casing string to create a robust, gas-tight barrier. This paper presents the deployment and performance evaluation of the TDAP technology in a 9-5/8″ × 13-3/8″ annular space, highlighting its effectiveness as a proactive solution for achieving long-term zonal isolation in gas wells.