Optimization of CO2 Storage under Geomechanical Risk with Coupled-Physics Models

Abstract

Summary Numerical flow simulation of CO2 injection into geologic formations that describe the fluid flow, transport, and trapping mechanisms have been used to optimize CO2 storage by improving trapping efficiency and injection strategies. However, CO2 storage in geologic formations can cause geomechanical changes that lead to reservoir expansion, ground surface uplift, and induced seismicity. Such deformations create geomechanical risks associated with CO2 injection, which can compromise the safety and storage capacity of CO2 injection in the field. The geomechanical responses from CO2 sequestration have drawn more attention in recent years due to considerable potential for ground uplifting and induced microseismic activities. An environmental sound and safe approach to CO2 storage must incorporate the geomechanical risks in optimizing the storage performance. We present an optimization framework for geologic CO2 storage under geomechanical risks, where coupled flow and geomechanical simulation is combined with rock failure criteria, such as Mohr-Coulomb plastic failure, to describe mechanical rock failure risk. Additionally, the outputs from geomechanical simulations are used to quantify the risk associated with the ground surface displacement and plastic strain. A multi-objective optimization is formulated and solved to maximize CO2 storage while minimizing the two forms of geomechanical risks. The optimization decision variables include the location and controls for each injection well. Multiple numerical experiments with increasing complexity, including a field-scale CO2-EOR example, are presented to demonstrate the performance of the proposed framework. The results reveal optimal decisions that are different from those obtained from flow-only simulation that disregard the geomechanical risks associated with CO2 injection. When geomechanical risks are considered, 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. Moreover, while surface uplift resulting from each well is highest at the corresponding injection locations, shear failure tends to happen in between the wells and its severity depends on formation properties as well as well configuration and controls. Overall, the observations from this study reveal important differences in optimization results and conclusions when geomechanical risks associated with geologic CO2 storage are considered.