COMPUTED TOMOGRAPHY ANALYSIS OF ALTERATIONS IN FRACTURED CAPROCK RESULTING FROM CO2-ACIDIFIED BRINE
To investigate the impact of leakage of CO2-acidified brine through caprock fractures, a flow-through experiment was conducted on a fractured sample of caprock. This caprock is a specimen of the Amherstburg formation in the Michigan sedimentary basin, and is a fine-grained carbonate composed primarily of calcite and dolomite. This formation overlies the Bass Islands Dolostone, the target formation for an injection demonstration project. The core sample was artificially fractured prior to the experiment and incased in epoxy to prevent lateral flow. Experimental temperature and pressure conditions were 40°C and 10 MPa, corresponding to injection at depths of approximately 1 km. The initial brine composition was representative of water previously reacted with the injection formation minerals under CO2-saturated conditions.
The flow-through experiment was conducted within a medical-grade CT scanner allowing for continued scanning of the core during active injection. Additionally, pre- and post-injection scans were taken with a micro-CT scanner providing voxel resolution of 27 µm, roughly five times better than that achieved via the medical scanner. Mineral dissolution along the fracture network is evident in both the CT imaging and analysis of brine effluent composition. After one week of brine flow, the micro-CT scans show increases in fracture aperture as large as 2 mm which in some cases is more than a 20-fold increase in aperture width. Further work will apply synchrotron-based x-ray diffraction CT and x-ray fluorescence imaging methods in an attempt to couple geochemical and spatial alterations within single pores along a flowpath. The ability to observe geochemical reactions at different scales provides the unique opportunity to relate how mineral dissolution and precipitation at the pore-scale impacts core-scale flow characteristics relevant to understanding the evolution of caprock integrity.