Performance Evaluation of Mineral Additive-Free Perfluoropolymer Nanocomposite O-Ring in Simulated Geothermal Environments at 300°C

摘要

This work evaluates the performance of O-rings made with a mineral additive-free perfluoropolymer (FFKM) nanocomposite in mitigating silica- and silicate-scales, inhibiting oxidative reactions, minimizing the changes in mechanical behaviors, and maintaining the integrity of O-rings after their exposure to five different simulated geothermal environments at 300°C. For comparison, various mineral additive-filled EPDM, FEPM, and FFKM composite O-rings were employed. The tensile strength and ultimate elongation of the mineral-free nanocomposite O-ring were equal to, and even higher than those of the mineral additive-filled composite O-rings. The magnitude of silica- and silicate-scaling on O-ring surfaces was governed by: 1) The oxidation reactions of the -CH_2- groups; 2) the incorporation of oxidation derivatives, such as C=C, C=O, and COO" groups; and, 3) the water uptake by the mineral additive and the degraded polymer. Among the tested environments, the geo-brine fluid caused the highest precipitation of these scales. The water uptake by O-rings was due to both their oxidative degradation and the presence of mineral additives. In contrast, mineral-free FFKM nanocomposite did not absorb any water in all environments, demonstrated a low susceptibility of -CH_2- groups, the minimal rate of oxidation, and the limited scaling. The high rate of scale deposition strongly affected mechanical behaviors of the O-rings. In the thermal shock tests, the degradation of the O-ring was promoted by the sensitivity of mineral additives to the reaction with CO_2(gas) leading to the dry carbonation. EPDM underwent very high oxidation, allowing water to permeate through it. The mineral additive-free FFKM nanocomposite displayed the best performance in maintaining the integrity of O-ring in all test environments demonstrating a high potential not only for O-rings use, but also for gaskets, seals, and packers.