Sensitivity analysis of geological and engineering parameters for CO2 storage in saline aquifers based on numerical simulation

Zhang Helong; Liu Shiqi; Tian Yuchen; Wang Wenkai; Sang Shuxun; Zheng Sijian; Li Bing; Chen Yongchun

doi:10.16186/j.cnki.1673-9787.2025060017

Abstract：Objectives This study is conducted to investigate the coupled evolution of reservoir porosity-permeability and multiple CO2 trapping mechanisms in the CO2-brine-rock system,with the unclear syner-gistic mechanisms among different trapping methods and the sensitivity of key geological and engineering parameters during CO2 sequestration in saline aquifers being addressed.Methods A 100-year numerical simulation(including a 10-year injection period)is performed using the TOUGHREACT software with the ECO2N module.The model is applied to the deep saline aquifer of the Ordovician Majiagou Formation in the Gubei Mine of the Huainan Coalfield.Furthermore,a parameter sensitivity analysis is designed to fur-ther elucidate the influence of key geological(reservoir anisotropy,salinity)and engineering(CO2 injec-tion rate)factors on the efficiency of these CO2 trapping mechanisms.Results Results demonstrate that the maximum lateral extent of the CO2 plume reaches approximately 1000 meters over the simulation period.CO2 injection reduces pH to 5.36 near the injection well,leading to the dissolution of dolomite,which re-leases Mg²⁺ and inhibits calcite precipitation.This indirectly enhances dissolution processes,resulting in porosity and permeability increases of 0～0.52%and 0～1.6%,respectively.Structural trapping is identified as the dominant mechanism,followed by residual(16.9%),solubility(3.9%),and mineral trapping(0.5%).Sensitivity analysis indicates that higher CO2 injection rates enhance the overall storage capacity.Greater initial brine salinity intensifies buoyancy-driven migration,thereby increasing structural trapping,while salt-out effects suppresse solubility trapping.When the horizontal-to-vertical permeability ratio(kh/kv)increases from 1 to 100,residual and solubility trapping rise by 43.1%and 34.3%,respectively.An in-creased kh/kv ratio alters CO₂ distribution and phase partitioning,shifting the dominant trapping mecha-nism from structural dominance to a combination of physical and geochemical processes.Conclusions Struc-tural trapping is confirmed as the primary mechanism for CO2 sequestration in deep saline aquifers.Geo-chemical reactions influence the porosity-permeability structure through a cycle of mineral dissolution,ion migration,and precipitation.Reservoir anisotropy,brine salinity,and CO2 injection rate can be optimized to regulate fluid flow pathways and phase distribution,thereby enhancing the storage effectiveness of mul-tiple CO2 trapping mechanisms.