Publications Details

Evaluation of High Temperature Elastomers for Geothermal Wells

Redline, Erica M.; Sugama, Toshifumi; Pyatina, Tatiana

This report describes the extension of a performance screening study of elastomers for geothermal well applications. Elastomeric O-rings were subjected to compression while submerged in water at elevated temperatures and pressure to determine performance under more aggressive conditions. Following the experiment, the elastic moduli of the O-ring cross-sections were assessed for any changes which may affect O-ring function down-hole. All materials showed susceptibility to thermo-oxidative degradation at high temperatures and pressures. Type I FKM had the least amount of compression set of all materials tested at 150ºC while Kalrez FFKM O-rings had the least amount of edge hardening of all materials, regardless of aging temperature. Prior visual observation of materials aged in simulated environments revealed an unusual trend with EPDM and FEPM materials: the degradation and disintegration of these polymers in an oxidative thermal cycle environment, but the ability to maintain mechanical performance and shape during oxidative thermal cycling in the presence of steam. EPDM and FEPM were subjected to additional testing at SNL in order to better understand this aging anomaly. No abnormalities were observed in the chemical (oxidation rates, FTIR spectra, solvent uptake, gel content, and weight loss vs. temperature) or physical (modulus profiles) measurements that could explain the visually observed aging differences. SNL validated this observation through a secondary controlled aging test using only EPDM, where, once again, it was shown that thermo-oxidative conditions appear to cause more degradative damage (enhanced embrittlement) than did thermo-oxidative coupled with hydrolytic environments. From these data we conclude that water may favorably interfere with normal thermo-oxidative degradation processes via some type of inhibition pathway which has yet to be identified.