Degradation of different elastomeric polymers in simulated geothermal environments at 300°C
Sugama, Toshifumi; Pyatina, Tatiana; Redline, Erica M.; McElhanon, James R.; Blankenship, Douglas A.
This study evaluates the degradation of six different elastomeric polymers used for O-rings: EPDM, FEPM, type I- and II-FKM, FFKM, and FSR, in five different simulated geothermal environments at 300°C: 1) non-aerated steam/cooling cycles, 2) aerated steam/cooling cycles, 3) water-based drilling fluid, 4) CO2-rich geo-brine fluid, and, 5) heat-cool water quenching cycles. The factors assessed included the extent of oxidation, changes in thermal behavior, micro-defects, permeation of ionic species from the test environments into the O-rings, silicate-related scale-deposition, and changes in the O-rings' elastic modulus. The reliability of the O-rings to maintain their integrity depended on the elastomeric polymer composition and the exposure environment. FSR disintegrated while EPDM was oxidized only to some degree in all the environments, FKM withstood heat-water quenching but underwent chemical degradation, FEPM survived in all the environments with the exception of heat-water quenching where it underwent severe oxidation-induced degradation, and FFKM displayed outstanding compatibility with all the tested environments. This paper discusses the degradation mechanisms of the polymers under the aforementioned conditions.