Controlled CO2 Injection into Storage Reservoirs to Minimize Geomechanical Risks Under Geologic Uncertainty

Abstract

Abstract Carbon Capture and Storage (CCS) has gained recognition as a mitigation strategy for reducing the accumulation of atmospheric CO2. However, the injection of CO2 into storage reservoirs can lead to increased pore pressure, which in turn induces stress changes in and around the injection site. These stress changes may give rise to several geomechanical hazards, including caprock failure, ground surface uplifting, and induced seismic activity. To address this concern, we have developed a novel optimization approach aimed at maintaining the caprock integrity during the storage of CO2 in geologic formations under geological uncertainty. The developed workflow integrates advanced numerical optimization algorithms with coupled multiphase flow-geomechanics-fracturing models for simulating the response of the storage reservoir to CO2 injection. Using the geomechanical response of the simulation, we define and quantify the potential caprock failure and CO2 leakage risks. An optimization formulation is used to minimize the risk of caprock fracturing and CO2 leakage by finding the optimal distribution of dynamically changing CO2 injection rates across several wells throughout the injection period. The results are extended to incorporate the uncertainty in the simulation model through ensemble-based optimization. The proposed optimization approach identifies the well injection schedule (flow rate vs. time profile) to minimize the risk of caprock fracturing by distributing the pressure increase in the heterogeneous reservoir. The optimization process is designed to continually enhance the injection strategy, aiming to minimize the potential for caprock fracturing by maximizing the stress differences between the minimum effective stress and the fracture opening stress. The paper highlights the importance of employing coupled flow and geomechanics, along with fracture mechanics, in accurately modeling and predicting the potential CO2 leakage. This approach enables the development of injection strategies that prioritize caprock integrity, effectively addressing the challenges associated with optimizing CO2 storage while minimizing the risk of caprock failure.