Impact of Carbon Storage Environmental Exposures on Elastomeric Sealing Performance and the Effectiveness of Dynamic Mechanical Analysis Results as a Predictor

The impact that four simulated subterranean gas storage environments have on the sealing performance of common elastomeric materials used with oil and gas completions tools is characterized. In addition to an outline of the environmental changes observed with each material, sealing capabilities after environmental exposure and the effectiveness of dynamic mechanical analysis (DMA) as a predictor is examined, which, when effective, simplifies environmental compatibility assessments. Commercial 90 Shore A durometer elastomeric base material compounds, to include NBR, HNBR, EPDM, and FKM as defined in ASTM D1418, were evaluated for chemical stability. Unstressed material specimens, to include ISO3601-1 standard sized −325 O-rings, were aged in three simulated carbon storage environments, which included supercritical carbon dioxide (SCCO2) dry, in the gas and liquid phases with water, and a hydrogen storage environment in the gas phase with water for a maximum of 60 days at 95°C and 100 bar. Upon conclusion of these exposures, the materials were characterized in their original and aged conditions by a DMA thermal sweep from −100 to 100°C and performance tested under fixed geometric configurations using hydraulic test media for both elevated temperature extrusion resistance and low-temperature sealing. Changes, both positive and negative, were observed during pressure tests and the predictive accuracy of the DMA output parameters were highly dependent on each material's sensitivity to environmental exposure. Extrusion to failure results directly correlated with the storage modulus when exposed to chemically aggressive environments while experimental noise tended to dominate for chemically stable materials. Glass transition temperature (Tg), a common reference parameter for the low-temperature performance of polymeric systems, was evaluated using the storage modulus onset, and Tan δ peak by DMA as well as the midpoint of the endothermic transition of the amorphous phase by differential scanning calorimetry (DSC). Modulus and Tg shifts directionally aligned with expectations for with low-temperature sealing, but neither evaluation independently was sufficient to account for the sealing performance changes. An engineering assessment of critical inputs and the mathematical technique of dimensional analysis was introduced to generate a master curve for sealing performance across the various material types and environmental exposures. Results illustrate how simulated well conditions, driven by operational protocols and relative equipment position, can influence the performance capabilities of materials and can be predicted using these methodologies. The effects that simulated gas storage environments have on the sealing performance of common oil and gas materials is discussed in addition to the effectiveness of DMA test outputs to predict sealing performance. Guidance on laboratory environmental exposure protocols is provided, critical material characteristic inputs for sealing performance are identified, and insight on the analysis of the test results as they relate to elastomeric performance in carbon storage wells is offered.