Defining the Geomechanical Operating Limits for Subsurface CO2 Storage

Carbon capture and storage (CCS) is a critical component of proposed pathways to limit global warming, though considerable upscaling is required to meet emissions reductions targets. Quantifying and managing the risks of fault reactivation is a leading barrier to scaling global CCS projects from current levels of ~40 MtCO2/yr to target levels of several GtCO2/yr because CO2 injection into reservoirs can result in increased pore fluid pressure and temperature changes, which can reduce the strength of rocks and faults, and induce brittle failure. This can result in induced seismicity, whilst hydraulic fracturing of overlying sealing formations could provide pathways for CO2 leakage. Consequently, identifying favourable geomechanical conditions (typically determined through data on pre-injection rock stress, mechanical and elastic properties and pore-fluid pressures) to minimise deformation of reservoirs and seals represents a key challenge in the selection and de-risking of safe and effective sites for CCS projects. Critically however, such geomechanical data are typically spatially limited (i.e. restricted to wells) and mainly consist of pre-injection crustal stress orientation measurements, rather than a full 3D description of the stress tensor and related geomechanical properties. This paper provides a concise review of some of the key geomechanical issues and knowledge gaps (particularly those associated with data availability and limitations) that need to be understood to enable successful reservoir and seal management, and ultimately long-term storage efficacy, for CCS projects. We also highlight recent advances in multi-scale and dimensional geomechanical modelling approaches that can be used to assess sites for the secure storage of CO2, and other gases including hydrogen.