In this study, we aim to quantify the changes in fracture permeability and flow velocity fields caused by exposing a fractured carbonate caprock sample to CO2-acidified brine flow. Before and after a flow-through experiment, X-ray computed micro-tomography scans were taken. The images were segmented and processed to reconstruct the initial and final fracture geometries. 1-D empirical equation, 2-D steady state flow model, and 3-D computational fluid dynamics (CFD) simulation were applied on the reconstructed fracture geometries to estimate the intrinsic permeabilities prior to and after the experiment. The capabilities of the 1-D empirical equation, 2-D steady state flow model and 3-D CFD simulation in quantitatively capturing the permeability evolution are also examined. Furthermore, comparing the detailed pre- and post- fluid velocity field provides important insights on the direction of local geochemical reactions. The simulation results serve to deepen our understandings of the modification of fracture hydraulic properties by CO2-acidified brine flow, and hence to improve our predictive capability on evolution of caprock integrity and leakage risks.
Modification of Fracture Hydraulic Properties by CO2-Acidified Brine Flow
Geological storage of CO2 is a promising option for carbon mitigation, but its application faces challenges such as the possibility of CO2 leakage. Quantification of the leakage risks requires characterization of the porosity and permeability of the porous media, and prediction of dynamic evolution of these properties caused by rock-CO2-brine interactions. Fractures in porous media are of special interest as they can be created, activated and propagated during CO2 injection (e.g. In Salah CO2 storage site). Moreover, they serve as preferential-flow pathways, and allow constant flushing of the solutes, which may lead to enhanced rock- CO2-brine reactions.
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