Mitigating caprock failure and leakage risks through controlled CO2 injection and coupled flow-geomechanics-fracturing simulation

Abstract

During CO₂ injection into geologic storage formations, pressure increase induces stress changes in and around the reservoir, which may cause various geomechanical hazards such as caprock failure, ground surface uplifting, and induced seismicity. Caprock failure may create a leakage pathway for CO₂ to leak from the storage reservoir to shallower aquifers and even to the atmosphere. Identifying injection strategies that ensure the safety of operation in the presence of such risks is a challenging problem. In this paper, we present a novel framework for minimizing the CO₂ leakage potential due to caprock fracturing. We develop the framework by intgerating a coupled multiphase flow-geomechanics-fracturing simulation of geologic CO₂ storage process with an advanced numerical optimization algorithm that effectively utilizes the multiphysics mechanisms inherent in the model. The proposed optimization framework incorporates geological uncertainty to account for the lack of complete knowledge about the storage formation flow properties. The optimization algorithm determines the optimal well injection rate trajectories over uncertain descriptions of a heterogeneous storage reservoir to manage the pressure increase and minimize the risk of fracturing and CO₂ leakage. To minimize the caprock fracturing potential, the optimization algorithm maximizes the stress differences between the minimum effective stress and the fracture opening stress. The paper demonstrates the importance of applying optimization algorithms to systematically minimize the leakage risk. This is accomplished through a numerical optimization algorithm that uses a state-of-the-art coupled-physics modeling to search for and identify injection strategies that do not jeopardize caprock integrity. The presented approach is generic and can be adapted to minimize other environmental risks associated with geologic CO₂ storage.