Numerical Simulation of Effects of Microbial Action on CO2 Geological Storage in Deep Saline Aquifers

CO2 geological storage (CGS) is a crucial strategy for meeting CO2 emission reduction targets. However, the effect of microbial action on CGS in deep saline aquifer is unclear. In this paper, numerical simulations based on previous experimental data were conducted to investigate CO2 solubility-trapping and mineral-trapping by microbial-mediated process in CGS demonstration base in Ordos, north of China. The simulation results reveal that the presence of a microbial community has a positive influence on CGS, mainly in terms of the amount of CO2 that can be injected and the manner by which it is stored. With the effect of microbial action, the amount of injected CO2 was increased by 23.33% and the CO2 mineral sequestration increased from 1.12 to 2.05%. In addition, microbial action plays different roles at different stages of CGS. In the initial stage of CO2 injection, the microbial action promotes dissolution of calcite, oligoclase and clay minerals such as chlorite and kaolinite, providing a favorable condition (more K+, Ca2+, Na+, Mg2+, Fe2+ and HCO3-) for CO2 mineral-trapping. In the following stage of CGS, microbial action accelerates the precipitation of carbon-fixing minerals such as calcite and siderite, enhancing the CO2 storage security in deep saline aquifer. As such, secondary minerals such as ferroan dolomite and dawsonite were observed in advance in microbially mediated CO2-saline-sandstone interactions, further indicating that microbes play a positive role in CO2 mineral-trapping. Consequently, the microbial action can promote mineral capture of CO2 and increase the CO2 storage security in deep saline aquifer. These conclusions can provide a reference and basis for the suitability assessment of CGS in such deep saline aquifer like Erdos, China.