Rapid Gas Decompression RGD and Sealing Performance of Elastomer Seals in Oil and Gas Field

Abstract

Abstract The objective of this study was to investigate the relationship between rapid gas decompression (RGD) damage and sealing performance of elastomer seals in simulated well conditions; hence, develop useful advice for dealing with the impact of RGD damage on sealing performance. The goal is to obtain an improved seal validation program. Radially energized rounded-face nonextrusion elastomer seals (or S-seals) and metal endcap seals (MEC seals) fabricated from nonRGD-resistant grades of elastomers were used for this study. The RGD damage to elastomer seals made from hydrogenated nitrile-butadiene rubber (HNBR) materials for wellheads, Christmas trees, and frac tree applications were investigated according to ISO 23936-2, NORSOK M-710, and API 6A Annex F PR2 test procedures. The in-situ sealing performance was evaluated after the RGD exposure to determine the relationship between RGD damage and sealing performance. The test results revealed that the S-seals showed significant RGD damage. The RGD ratings were found to be similar to standard RGD test results based on NORSOK M-710 for the same elastomer. It is noteworthy that all of the seals could still hold pressure in sealing pressure validation tests at both room temperature and 100°C, even though the RGD damage to the seals was significant. These results revealed that the conventionally acceptable criteria based on ISO 23936-2 and NORSOKM-710 are not suitable for the pressure validation test of an actual seal. As for the RGD question during API 6A Annex F PR2 test, the MEC seals also showed extensive RGD damage, which only affected the PR2 test performance significantly at lower temperature, further demonstrating that the sealability of seals is heavily influenced by test conditions such as test temperature. In conclusion, the RGD rating acceptance criteria per ISO 23936-2 and NORSOK M-710 is not representative of the application of a seal.