Effects of the mechanical response of low-permeability sandstone reservoirs on CO geological storage based on laboratory experiments and numerical simulations.

Carbon dioxide (CO) geological storage (CGS) is an effective way for reducing greenhouse emissions. The injection of CO into the deep formation changes the pore pressure and effective stresses in the reservoir, thus leading to changes in stress-dependent porosity and permeability. These changes give feedback to the injection rate, migration, storage amount of CO in the target reservoir. In this study, we focus on the Liujiagou reservoir, one of the first demonstration CGS project in saline aquifers in the Ordos Basin, China. The mathematical model that defines the relationship between the permeability and the injection pressure (or effective stress) was obtained by laboratory experiments. On this basis, the permeability-stress law was successfully integrated into the thermo-hydro-mechanical (THM) coupled simulator TOUGH2Biot to simulate the feedback between the flow and mechanical response. The improved simulator was used to analyze the effects of reservoir mechanical response on CO geological storage efficiency. The modeling results indicated that the mechanical response of the reservoir had little effect on reservoir pore pressure and porosity, but it had a significant effect on reservoir permeability and the migration distance, injection rate, and total storage amount of CO. The maximum increases in the lateral migration distance of CO caused by the reservoir mechanical response reached 13.1% using 5 MPa injection pressure. In addition, the total CO storage amount increased by 11.6% after 5 years of continuous CO injection. Furthermore, when the injection pressure was greater, the reservoir mechanical response had stronger enhancement effects on CGS. Overall, the results suggested that the reservoir mechanical response during CO injection was beneficial for increasing CGS efficiency and emphasized the importance of considering the mechanical response in CGS.