Numerical Simulation of In-Situ CO2 Mineralization in Mafic Basaltic Formations in Southwest Oklahoma

Abstract

Power plants and other industries in Oklahoma produce a huge amount of CO2 emissions that should be mitigated for environmental benefits. One method to mitigate these emissions is permanent CO2 sequestration through mineralization. CO2 can be mineralized in the subsurface if injected into iron- magnesium-rich igneous formations that form carbonate minerals. In Southwest Oklahoma, there are several mafic basaltic formations that can be targeted for CO2 storage. The objective of this study is to quantify carbon storage through mineralization in Southwest Oklahoma. In this study, we built a carbon sequestration numerical model to simulate the geochemical reactions of injecting CO2 into a saline aquifer. The model includes three main geochemical reactions: CO2 dissolution in water, dissolution of formation minerals, and precipitation of carbonate minerals. The first reaction results in forming carbonic acid that reacts with the formation minerals: anorthite, wollastonite, pyroxene, and olivine, which results in releasing calcium and magnesium ions. The reaction between free ions in the formation of water and dissolved CO2 results in precipitating carbonate minerals: magnesite and calcite. CO2 is injected into the formation for four years and simulated for the next 200 years. The rate of dissolution and precipitation was monitored as a function of time. In addition, the reservoir parameters: porosity, permeability, and reservoir pressure, were analyzed as a function of time and precipitation rate. The results show that 97% of the injected CO2 is mineralized, and the rest is residually trapped and dissolved in water. Due to the mineralization of CO2 in the form of magnesite, and calcite, the porosity decreased by 5% maximum due to the extra cement in the pore space. The reservoir pressure increases during the injection, but it decreases rapidly after due to the quick CO2 mineralization. Lower reservoir temperature increases the amount of CO2 mineralized due to the higher CO2 solubility in water. In addition, changing the activation energy of mineral reactions leads to a change in the dynamics of CO2 mineralization, but the net of CO2 mineralization changes slightly. The carbon storage numerical model built for this study considers the effect of the formation water chemistry and rocks mineralogy on the amount of CO2 sequestrated. In addition, it shows that Oklahoma can lead to carbon sequestration in basaltic formations.