Analytical model for fines migration due to mineral dissolution during CO2 injection

Abstract

Recent laboratory studies have proposed carbonate mineral dissolution as a main mechanism for fines migration during CO2 injection. However, existing mathematical models of fines migration ignore mineral dissolution as a mechanism for fines generation. To address this gap, we derive a basic system of governing equations that incorporate fines migration induced by mineral dissolution. An analytical solution is derived for four zones defined based on normalized porosity and carbonate mineral concentration profiles. These profiles are then used to derive the suspended and retained fines concentrations. The analytical solution is found to be in close agreement with the numerical solution of the basic system of governing equations. To validate our model, we perform injection experiments on four Berea sandstone cores. Each core receives injection of CO2-saturated water of designated salinity 0, 0.17, 0.51, or 1.03 M NaCl.The results suggest that two competitive phenomena occur due to carbonate mineral dissolution during CO2-saturated water injection, i) increased porosity that is responsible for the increase in permeability and ii) fines migration that results in permeability reduction. Dissolution of intergranular cement results in fines dislodge, some of which subsequently cause pore blockage and permeability reduction.For 0, 0.17, and 0.51 M salinity, mineral dissolution is found to be dominant, yielding a net increase in rock permeability due to increased porosity. For 1.03 M salinity, higher dissolution rates are found to cause significantly more fines, yielding a net decrease in rock permeability. The comparison of experimental and modelling data shows high agreement with the experimental data, which validates the proposed model.