Experimental Investigation of CO₂-Induced Geochemical Interactions in Fractured Deccan Basalts

This study investigates the evolution of microfractures in basalt formations from Deccan Traps, India, after exposure to CO2 under reservoir conditions. Artificially fractured cores were subjected to 72-day static batch experiments with aqueous CO2 to induce geochemical interactions between fracture surfaces. Postreaction flow-through tests were conducted to assess changes in flow properties, quantified using differential pressure (DP) sensors. Core samples were characterized before and after the reaction using micro-XCT imaging and SEM-EDS analysis. All samples exhibited a systematic increase in flow resistance. Hydraulic conductance decreased by 28–50% in the dyke basalt cores and by 13–26% in porphyritic basalt cores, with more pronounced reductions under higher confining pressure (20 MPa). Micro-XCT imaging revealed a bimodal redistribution of fracture apertures after the reaction period, with increases in both small (<60 μm) and large apertures (>150 μm) and a decrease in intermediate ones (<60 and > 150 μm). This evolution was attributed to spatially heterogeneous dissolution–precipitation dynamics, where dissolution was localized near fracture inlets and precipitation occurred in the core interiors with restricted fluid mobility, particularly in dyke samples. As a result, the fracture network evolves into a more restricted and directed flow system, where only a few higher-conductivity channels control the movement of the fluid. The study highlights the importance of incorporating dyke-specific geochemical behavior into the design and long-term management of carbon storage projects in basaltic reservoirs.