Investigating the Interplay of Injection-Induced Stress on Reservoir Dynamics and Caprock Integrity in San Juan Basin Carbonsafe Site

Abstract The subsurface injection of CO2 into saline aquifers is a critical method for carbon sequestration aimed at reducing atmospheric CO2. The geomechanical impacts of CO2 injection, particularly injection-induced stress on reservoir and caprock integrity, present significant risks and require thorough investigation. This research investigates the impact of stress changes on the long-term structural stability of the caprocks and the integrity of the Entrada formation in the San Juan Basin. A hydrodynamic model representing the formation of interest was constructed using geophysical log data and calibrated using injection and bottom hole pressure data of 22 nearby saltwater disposal wells within the study area. 1D mechanical earth model along the stratigraphic well was integrated with 3D seismic elastic inversion data to generate a 3D mechanical earth model. A two-way coupled geomechanics-hydrodynamic simulation was performed incorporating the Kozeny-Carman stress-dependent permeability correlation to understand the changes in permeability and effective stress dynamics with the increase in reservoir pressure due to the CO2 injection. The capillary entry pressure and stress-strain responses of the caprocks were evaluated for risk assessment. The stress path, stress redistribution, critically stressed areas, and formation uplift caused by CO2 injection were identified. The results show significant reduction in effective stress and displacement within 1 mile from the injection point. Stress-induced changes of the caprock reservoir interface showed a 5% decrease in effective stress. Analysis of the two-way coupled simulation showed an increase in the porosity with subsequent increase in permeability of the reservoir with negligible permeability update of the caprock and hence no conduit for CO2 leakage. The results also highlight that the northwestern section of the formation experiences the highest stress compared to other parts due to hogback monocline structure. Though the increase in the pore pressure caused stress redistribution within the caprock, its integrity remains undisturbed. The capillary entry pressure was found to be sufficiently high, preventing CO2 from penetrating the caprocks, thus ensuring that the CO2 injection does not compromise the seals above. This study presents a detailed analysis of the geomechanical effects of CO2 sequestration on reservoir fluid dynamics, stress redistribution, and rock mechanical properties dynamics within the San Juan Basin. It evaluates the long-term geomechanical behavior of the formation with particular attention to stress-induced deformation and caprock integrity. The findings highlight the importance of coupled geomechanical-hydrodynamic modeling in assessing injection-induced stress alterations and their implications for caprock stability, enhancing risk assessment of CO2 sequestration, paving the way for the development of reliable geologic carbon storage practices.