Structural Control of a Dissolution Network in a Limestone Reservoir Forced by Radial Injection of CO2 Saturated Solution: Experimental Results Coupled with X-ray Computed Tomography

This study was conducted in the framework of the PILOT CO2-DISSOLVED project, which provides an additional approach for CO2 sequestration, with the aims of capturing, injecting, and locally storing the CO2 after being dissolved in brine. The brine acidity is expected to induce chemical reactions with the mineral phase of the host reservoir. A set of continuous radial CO2 flow experiments was performed on cylindrical carbonate rock samples under geological storage conditions. The objective was to interpret the dissolution network morphology and orientation involved. To explore the three-dimensional architecture of dissolution arrays and their connection integrity within core samples, we used computed tomography. A structural investigation at different scales revealed the impact of the rock heterogeneity on the dissolution pathways. The initial strike of the observed mesoscopic wormholes appears to be parallel to dilatational fractures, with a subsequent change in major trends of dissolution along master shears or, more specifically, a combination of synthetic shears and secondary synthetic shears. Antithetic shears organize themselves as slickolitic surfaces, which may be fluid-flow barriers due to different mineralogy, thus affecting the permeability distribution-wormhole growth geometry induced by CO2-rich solutions.