Analysis of the Permeability Change Resulting from Active Mineral Precipitation in Pores of Rocks by 3D-DEM

Abstract

Carbon dioxide capture and storage (CCS) is a promising technique for reducing the concentration of CO2 in the atmosphere, and several million tons of CO2 are sequestered every year. The most important problem in CCS is ensuring aquifer safety. However, there is still room for improvement in the flow characteristics of aquifers to prevent CO2 leakage. To decrease the permeability of porous rocks, in this study, a method called ‘active mineral deposition’ was developed. In this method, some minerals are actively precipitated in aquifers, and the pores in the rock mass are closed by precipitated minerals. Because the pores are closed and stacked by minerals, the permeability of the rock mass is expected to decrease. For the precipitated minerals, CaCO3 is a promising mineral, and CaCO3 is precipitated in the pores of rocks. From microscopic observation, the approximate size of the precipitated mineral was estimated to be 10 μm in the rock pores. To verify the effect of the method, the permeability of the porous rocks was simulated using the three-dimensional discrete-element method (3D-DEM). Here, the rock minerals and pores were simulated using DEM elements, and the initial permeability of the models was estimated. Then, the small minerals, which represent precipitated minerals, were generated in the pore space, and changes in the intrinsic permeability, flow path, and pressure distributions in the rocks were estimated. The value of intrinsic permeability decreased to one tenth of the initial condition when 1% of the pore spaces were occupied by the precipitated minerals. A small amount of precipitation could change the permeability of the porous materials.