Coupled Processes in a Fractured Reactive System: A Dolomite Dissolution Study with Relevance to GCS Caprock Integrity

Predicting the temporal evolution of fractures in impermeable sealing units above geological carbon storage reservoirs is crucial to understanding leakage risk as well as optimal selection of storage sites. Process models are required which couple geochemical, hydrological, and mechanical effects to predict whether transmissive fractures increase or decrease in permeability during exposure to CO2 or CO2 ‐saturated brines. We present results from a unique flow‐through experiment conducted to image fracture evolution in a dolomite sample with dynamic synchrotron X‐ray microtomography (SXR‐micro‐CT) at appropriate stress states. The results of the experiment show localized aperture enlargement and development of a microporous weathered zone due to rapid dissolution of calcite crystals, consistent with prior observations. Surface roughening and fines mobilization were also observed during dissolution. Confining stress cycles conducted after initial flow confirmed that the asperities remained strong even after exposure to aqueous CO2 for prolonged periods. Geochemical analysis of effluent samples shows an increasing rate of dolomite dissolution with time, likely due to early buffering by calcite dissolution and increasing reactive surface area. The resulting measurements are consistent with a simplified reactive transport model and will be used to calibrate high‐resolution models of near‐fracture processes in the context of geologic carbon storage.