Quantification and Incorporation of Geomechanical Risks in Optimization of Geologic CO2 Storage Using Coupled-Physics Models

Abstract

Abstract Numerical flow simulation models for CO2 injection, transport and trapping mechanisms have been used to optimize geologic CO2 storage (GCS) by improving trapping efficiency and injection strategies. Injection of CO2 into geologic formations can cause geomechanical changes and lead to reservoir expansion, ground surface uplift, and induced seismicity. Such deformations create geomechanical risks associated with GCS, which can compromise the safety and storage capacity of CO2. The geomechanical risks of CO2 sequestration have drawn significant attention in recent years due to considerable ground uplifting and induced microseismic activities that have been reported in several field cases. However, studies in this area have not considered the effect of geomechanical risks in optimizing the storage performance. We present an optimization framework to strategically place CO2 injection wells to maximize the storage capacity and minimize the associated geomechanical risks. To this end, we perform the optimization using three-dimensional coupled flow and geomechanical models, by applying the Mohr-Coulomb plastic failure criterion to model mechanical rock failure risk. Additionally, the geomechanical simulation results are used to quantify the risk associated with ground surface displacement and plastic strain, which are extracted from the simulation outputs. A multi-objective optimization problem is formulated to maximize CO2 storage while minimizing the two forms of geomechanical risks. The injection well locations are defined as decision variables and Genetic Algorithm is implemented to solve the multi-objective optimization problem. The solution of the proposed framework leads to nontrivial optimal decisions, which are different from the case where geomechanical risks associated with CO2 injection are ignored. We find that the wells may not necessarily be concentrated in areas with the highest storage capacity because that may lead to rock failure and unacceptable levels of ground surface uplift. Instead, the maximum storage is limited to keep the reservoir in the elastic state based on the specified reservoir geomechanical and flow properties. We also observe that well interactions during CO2 injection can cause shear failure of the formation between the wells. These observations suggest that accounting for geomechanical risks associated with CO2 injection is necessary to design a sustainable plan for CO2 injection and storage. The paper ends with a discussion about the importance of accounting for the uncertainty in rock properties and the resulting model predictions in optimizing the well locations.