Hydraulic Behavior of Fractured Calcite-Rich Sandstone After Exposure to Reactive CO2–H2O Flow

Abstract

Geological carbon sequestration in jointed reservoirs will require the use of fracture network for the flow of CO2 plumes. However, acidic solution formed at the interface between brine and CO2 can cause chemical erosion of the local rock mass, especially in rocks with high carbonate content. The use of the water alternating gas technique for injection stimulation can exacerbate this issue, as the water–CO2 interface occurs in areas near the injection point. As a result, acidic flow can impact the surrounding rock mass, particularly around the main flow paths where fracture network conductivity is much higher than matrix permeability. To investigate the impact of acidic flow on fracture conductivity, we conducted an experiment on a fractured sandstone sample that was exposed to CO2-saturated water. Our findings revealed a nearly ten-fold increase in post-experimental water-relative permeability, and restriction of flow within established flow channels, which consist one third of the fracture surface. In conclusion, our study sheds light on the dynamic behavior of fractured sandstone under the influence of CO2–H2O flow, revealing significant changes in transmissivity and fracture geometry. These findings contribute to a better understanding of the hydraulic performance of fractures in the context of geological carbon sequestration.