Widely employed as a seal element in the oil and gas industry, understanding the aging behavior of Hydrogenated Nitrile Butadiene Rubber (HNBR) is crucial for both theoretical and practical advancements. This study investigates the degradation mechanisms of peroxide-cured HNBR compounds exposed to H2S and CO2 in a simulated environment at elevated pressure and temperature. Prior to accelerated aging, the mechanical properties and chemical structure of the samples were evaluated . Subsequently, the compounds were subjected to harsh aging conditions in Hc-A (5% vol. H2S and 20% vol. CO2) and Hc-B (20% vol. H2S and 5% vol. CO2) environments at high-pressure/hightemperature (HPHT) conditions of 6.9 MPa and 121°C, respectively. Fourier-transform infrared (FTIR) spectroscopy revealed significant changes in the molecular structure of the aged HNBR samples, resulting in increased swelling, reduced density of -C≡N groups and double bonds, additive migration, and a weakened reinforcing effect of carbon black. Furthermore, the study observed notable changes in the mechanical properties, including increased mass, volume, and elongation at break, but decreased hardness, modulus, ultimate tensile strength, and compression set compared to virgin samples. Notably, the results highlight the dominant influence of CO2 in the simultaneous sour gas immersion test on the structure-property relationship of the aged HNBR samples.

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