In this paper, conceptual modeling and numerical simulation of two-phase flow during CO₂ injection into deep saline aquifers is presented. The work focuses on isothermal transport and deformation processes in the vicinity of the injection well including hydromechanical failure analysis. Governing differential equations are based on balance laws for mass and momentum completed by constitutive relations for the fluid and solid phases as well as their interactions. Constraint conditions for the partial saturations and the pressure fractions of CO₂ and brine are defined. To characterize the stress state in the solid matrix the effective stress principle is applied. The coupled problem is solved using an in-house scientific finite element code, and verified with benchmarks.

In terms of application-oriented aspects, we examine the mechanical integrity of a deep saline aquifer during the injection of supercritical CO₂. The analysis is conducted with a numerical scheme of the capillary pressure and non-wetting phase pressure for the two-phase flow process. In this study, unidirectional hydromechanical coupling is considered. Caprock stability is monitored in time, referenced to the potential for hydraulic fracture and shear slip along an optimally oriented shear plane for a suite of injection pressures. For reasonable parameter values and the chosen aquifer geometry, significant mechanical failure (and potential breach of integrity) is expected in the shale caprock for all but low injection rates. This indicates that the analysis of the hydromechanical response is crucial for proper selection of injection sites, injection rates, and total storage capacity.