Sealing performance of rubber seals under extreme downhole conditions

Sealing rings are widely used in drilling and completion tools, but they are prone to performance degradation under combined high-temperature, high-pressure, and corrosive conditions, leading to sealing failure and leakage. This study investigates the high-temperature corrosion and high-pressure sealing performance of three sealing rings with identical specifications but different material systems: a fluorine rubber ring and two perfluoroether rubber rings, designated as S-FKM, S-FFKM-1, and S-FFKM-2. High-temperature corrosion tests were conducted, and the evolution of material properties was evaluated through systematic characterization of changes in morphology, mass, and hardness before and after corrosion. High-pressure sealing performance was further assessed using a specialized fixture, with sealing reliability determined by monitoring pressure variations. The S-FFKM-2 ring exhibited no cracking at 232 °C, with a mass change of 0.22 % and a hardness variation below 2 Shore A, demonstrating superior high-temperature corrosion resistance. The S-FFKM-1 ring maintained a pressure of approximately 67 MPa after corrosion at 180 °C, indicating excellent high-pressure sealing performance. In contrast, S-FKM showed intermediate behavior in both corrosion and sealing tests, reflecting a more balanced overall performance. The outstanding performance of S-FFKM-2 is attributed to its high tetrafluoroethylene content, while the high perfluoroalkyl vinyl ether and carbon black content in S-FFKM-1 contributes to its superior sealing capability. These findings provide valuable guidance for the selection of materials for high-temperature downhole sealing applications.