Influence of geochemical processes on the geomechanical response of the overburden due to CO2 storage in saline aquifers

Saline aquifers have been identified as desirable geologic formations, suitable for the storage of carbon dioxide (CO2) in large amounts. While the impermeable caprock layer(s) in the overburden provide(s) the primary trap for injected carbon dioxide, other trapping mechanisms, such as solubility, residual, ionic or mineral trapping, help contribute to CO2 storage. Geochemical reactions alter the petrophysical properties such as porosity in the target reservoir, and may have an influence on the reservoir storage capacity. When CO2 is injected for long periods of time, it changes the fluid pressures and the overburden geomechanical response. The geomechanical response associated with time-dependent geochemical reactions may also influence the integrity of the caprock layer and the long-term fate of injected CO 2.;In the current study, coupled multiphase fluid flow and geomechanical modeling with geochemical reactions was performed to simulate the long-term (1,000 years), large-scale injection of CO2 (up to10 million metric tons per year) into a deep saline aquifer. The primary objective of the study is to investigate the influence of geochemical reactions on the geomechanical response of the overburden during long-term CO2 injection. The geochemical modeling results show that geochemical reactions, such as mineral dissolution and precipitation, do not have a significant influence on reservoir rock porosity (about 2% reduction). However, an increase in the mineral reaction rate constants resulted in a reduction of about 35% in rock porosity. Modeling results show that the inclusion of geochemical reactions in the geomechanical models does not have a significant influence on the computed ground displacements during the injection and post-injection periods. However, brine salinity and CO2 solubility have an influence on the computed pressure buildup and ground displacements during CO2 injection. In this study, the influence of a vertical permeable zone (damage zone) around the wellbore on CO2 leakage during long-term CO2 injection was investigated. Modeling results show that the damage zone permeability and the vertical extent of the damage zone have a significant influence on the amount of CO2 leakage. Modeling results also show that the vertical extent of the damage zone does not have a significant influence on the computed ground displacements. Therefore, the computed ground displacements may not be a good indicator of the extent of damage zone around the wellbore