Effect of CO₂-enriched water on fracture pressure in Sandstone and Shale Rocks

Low-permeability reservoirs play an indispensable role in sustainable energy strategies; a good understanding of fracture behavior is essential. Fracture pressure is a critical parameter in hydraulic fracturing and reservoir stimulation, as it governs fracture initiation and propagation in tight formations. While numerous studies have investigated fracture pressure under conventional fluid injection, the impact of CO₂-enriched water (Carbonated water) remains poorly understood. This study addresses this gap by experimentally quantifying the effect of carbonated water on the fracture pressure of Kentucky Sandstone (quartz-rich) and Eagle Ford Shale (Calcite-rich) under controlled 90 °C conditions and no confining. Baseline tests used distilled water and then followed by carbonated water, which was prepared in an accumulator. Cores were exposed to carbonated water for 1 h and 24 h before testing. Breakdown pressure was identified from the pressure-time response during constant-rate injection. Carbonated water reduced fracture pressure from 2634 psi to 2214 psi in Kentucky Sandstone (15.9%) and from 3429 psi to 2479 psi in Eagle Ford Shale (27.7 %), with larger decreases after 24 h of exposure. The reductions are consistent with CO₂-driven geochemical weakening due to carbonate dissolution that lowers the tensile strength and closure stress. These results demonstrate that, even without confining stress and elevated temperature, interaction with CO₂-enriched water measurably lowers the fracture initiation pressure, providing actionable insights for the design of CO₂-assisted stimulation, EOR and CCUS operations in tight reservoirs. The technique of carbonated water is found promising, with the additional benefit that geochemical activity arises due to carbonated water.