Mohammad Nooraiepour , Hossein Fazeli, Mohammad Masoudi, Helge Hellevang

Chemical interactions between CO2, brine, and caprock-forming minerals might lead to dissolution of the fractures present in the caprock of CO2 storage sites. One factor that can affect the chemically induced fracture alterations is mineral heterogeneity in the caprock. In this study, we investigate the effect of mineral heterogeneity on fracture dissolution of four carbonate-rich caprock samples, having different levels of heterogeneity, where CO¬2-rich brine flows through the fractured caprocks. A HPHT geomaterial microfluidic experimental setup is used to monitor the evolution of the fractures. Results indicate that the homogeneous caprock samples, i.e. the samples that are mainly composed of calcite, show a uniform fracture wall dissolution while fracture wall roughness increases for heterogeneous samples. The effluent chemistry analyses show that the sample-scale calcite dissolution rate decreases over time, which can be due to the mass transfer limitations in the boundary layer near the fracture wall (for the homogeneous sample) or in the altered layer formed around the fracture (for the heterogeneous samples). Microfluidic experiments were also done for one carbonate rich finegrained shale sample, which showed no detectable fracture alteration. However, the effluent analysis for the shale sample confirmed the calcite dissolution.