Rapid Field-Scale CO₂ Storage Simulation Tool with Geomechanically Constrained Fault Leakage

Geological carbon dioxide (CO₂) storage is vital for climate change mitigation, but CO₂ leakage, particularly through faults, poses significant risks. Accurately simulating the impact of fault properties across scales is crucial for predicting field-scale CO₂ injection and storage outcomes. However, this task is challenging due to limited knowledge, data scarcity, and computational constraints. This study introduces a fast tool for CO₂ leakage risk assessment that addresses these challenges. The tool combines a vertically integrated reservoir model with an upscaled fault leakage function based on source/sink relations. It conceptualizes faults as zones of increased vertical permeability in the caprock and reduced horizontal permeability in the reservoir. A steady-state flow approximation estimates CO₂ leakage along faults. Geomechanical effects on fluid flow are modeled by coupling fault porosity and permeability, amongst several other parameters with effective stress using constitutive relations. A decoupled method based on Geertsma's uniaxial expansion coefficient, assuming zero lateral strain and constant total vertical stress is used here. Example simulations are shown to illustrate the impact of geomechanically constrained fault parameters such as capillary entry pressure and permeability on fault leakage. The fast model presented in this study is a valuable tool for identifying uncertainties in key fault parameters and other constitutive relations that affect the behavior of the storage reservoir and potential fault leakage outcomes. 1. INTRODUCTION Geological carbon dioxide (CO₂) storage, particularly in saline aquifers, is essential for mitigating climate change (Krevor et al., 2023). These aquifers have substantial storage capacities, but successful implementation relies on secure containment of CO₂. Leakage poses risks to mitigation efforts and undermines public trust in Carbon Capture and Storage (CCS). Faults are critical in this context, as they can either act as structural traps that confine CO₂ or serve as leakage pathways (Knipe et al., 1998; Snippe et al., 2021). As CCS deployment increases, encountering faulted storage formations is inevitable. Faults are complex geological structures with a low-permeability core surrounded by a fractured damage zone, which can increase leakage potential (Fig. 1) (Rizzo et al., 2024). Fault leakage is influenced by various factors, including geometry, architecture, stress regime, and rock properties. Injection-induced changes can reactivate faults, potentially creating new leakage pathways. Sub-seismic fractures within damage zones introduce significant uncertainties in CCS operations due to limited understanding of their presence and properties.