Environmental Stability Evaluation of Butadiene Copolymer Elastomers for Subterranean Gas Storage Applications

Abstract Various exposure strategies for elastomeric materials intended to mimic possible operational conditions in subterranean gas storage environments are presented in this study. The analysis focuses on the chemical stability and sealing performance of butadiene copolymer elastomeric materials used for oil and gas completions equipment in subterranean carbon and hydrogen storage wells. Commercial 90-durometer O-ring elastomeric compounds, which include NBR, HNBR, and a blend of SBR/BR, were evaluated for chemical stability in four simulated gas storage environments. These environments included supercritical carbon dioxide (SCCO2) in a dry state, in a gas phase with water, in a liquid phase with water, and hydrogen gas (H2) in a gas phase with water. Each condition was tested over intermittent durations and evaluated to a maximum of 60 days at an accelerated temperature of 95°C. Chemical, mechanical, and physical changes post-exposure were evaluated using common elastomeric laboratory analysis techniques and linked to seal performance using component-level tests. Results illustrate how well conditions, driven by operational protocols and equipment position, influence material selection and elastomeric compound design for well completions in subterranean carbon and hydrogen storage. In the examples discussed, one material proved agnostic to the specific exposure conditions, while others proved highly sensitive to phase location of the specimens. These materials, all butadiene copolymers, exhibited directionally opposite responses in some instances, particularly with shifts in the glass transition temperatures (Tg). These varied responses depended on both the compounded ingredients and the base polymer selection. Material evaluations, which included mechanical and analytical tests, provided insights into the chemical and physical changes observed in elastomer systems within carbon and hydrogen storage environments. Direct correlations to long-term seal performance emerged through component-level tests conducted in high-pressure test cells. Specific laboratory methods for the exposure of elastomeric materials to conditions in subterranean gas storage wells are discussed. Guidance on laboratory test setups to simulate the potential variety of environmental conditions in these wells, methods for the evaluation of polymeric materials post-exposure, and their effectiveness in seal performance in gas storage wells are also presented.