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ABSTRACT: Full-scale implementation of CO2 storage requires a number of challenges to be addressed, among them is reliably assessing geomechanical risk at storage sites. A 3D mechanical earth model (MEM) can be used to understand how rock types and stresses are distributed in the 3D space of the reservoir and surrounding formations. However, due to meshing limitations, the MEM is typically derived from simplified geological frameworks and does not relate with static and flow simulation models anymore. To overcome these difficulties, we have developed a general solution to readily assess the geomechanical risk of CO2 geological storage while preserving the geology’s integrity. We present a case study based on an offshore field in which the storage formation is composed of stacked anticlinal sandy layers sealed by shaly caprocks. We investigate fault stability by explicitly simulating the fault slippage and observe a significant fault reactivation with a maximum magnitude of ~ 0.3 m. A high resolution sub-model of the near-wellbore region indicates a stable wellbore condition. This workflow permits us to combine a reliable representation of the subsurface with a state-of-the-art rock mechanics finite element solver, which can be leveraged across the entire lifecycle of CO2 storage. 1. INTRODUCTION CO2 geological storage is a proposed solution to curb carbon emissions to the atmosphere (Bachu, 2008; Benson and Cole, 2008; Bickle, 2009). A large-scale CO2 storage project requires annual CO2 injection of millions of tons into deep geological media where the caprock and faults provide structural trapping of CO2 (Michael et al., 2010; Fuss et al., 2014; Tang et al., 2021; Wu et al., 2021). However, full-scale implementation of CO2 storage requires a number of challenges to be addressed, among them is reliably assessing geomechanical risk at storage sites (Rutqvist, 2012). For instance, CO2 injection increases the pore pressure and reduces the effective stresses, which may reactivate existing faults or induce damaging geomechanical changes to the caprock (Cappa and Rutqvist, 2011; Faulkner et al., 2018; Ju et al., 2021; Sun et al., 2021b). Fault reactivation is one risk of CO2 storage because it may compromise the sealing behavior as well as induce seismic events (Zheng et al., 2009; Apps et al., 2010; Zoback and Gorelick, 2012). Therefore, it is critical to maintain the integrity of caprock and faults to ensure the long-term CO2 storage security. |
