Performance of a granite-based two-part geopolymer in hydrogen sulfide-rich environments: Implications for sour wells

The long-term stability of wellbore sealants is crucial for the success of oil and gas operations. This study evaluates the performance of a low-calcium, granite-based two-part geopolymer (GP) system under hydrogen sulfide (H₂S)-rich brine exposure. GP samples were immersed in H₂S-saturated seawater at 100 °C and 11 bar for up to 12 months. Their mechanical, mineralogical, and microstructural integrity was assessed using unconfined compressive strength (UCS) testing, computed tomography (CT) scanning, X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and Fourier-transform infrared spectroscopy (FTIR). Results showed a progressive increase in UCS and Young’s modulus during exposure, coinciding with changes in mass, density, and microstructural features. CT scanning revealed surface-localized density reduction and preserved interior structure, highlighting spatial zonation rather than temporal densification. XRD analysis indicated increased relative crystallinity in H₂S-exposed samples compared to the initial cured state, while SEM-EDS revealed elemental redistribution and an increase in bulk sulfur content with exposure time, although no crystalline sulfur-bearing phases were detected within the resolution of XRD. The chemical form and binding state of sulfur could not be resolved with the applied techniques. Overall, the results indicate that the low-calcium, granite-based GP can retain mechanical integrity under prolonged H₂S-rich brine exposure, with degradation largely confined to surface regions, suggesting its potential as an alternative wellbore sealant in sour environments while recognizing that further studies with chemically equivalent controls are required to fully resolve underlying mechanisms.