Geomechanical Evaluation of Shale Caprock Integrity for Effective Carbon Storage: Focus on Sichuan Basin, China

Abstract Carbon capture and storage (CCS) relies on the integrity of the caprock to securely trap injected CO2 over geologic timescales. This paper presents a comprehensive geomechanical evaluation of shale caprock integrity in the Sichuan Basin of China, emphasizing factors that influence sealing capacity and long-term stability during CO2 storage. We integrate geological characterization, laboratory measurements, and simulation results to assess caprock performance under injection-induced stresses. The Sichuan Basin's geological and structural framework is reviewed, highlighting the basin's thick shale sequences (e.g., the Longmaxi Formation) and complex tectonic history. Key rock properties – mineralogy, porosity, permeability, strength, and elastic moduli – are compiled to establish baseline sealing capacity. In situ stress fields and the region's compressional tectonic setting are analyzed to understand the initial stress state of caprocks and faults. Experimental criteria for caprock failure, including Mohr-Coulomb shear failure and tensile fracturing, are evaluated using rock strength parameters from Sichuan shales. Geomechanical models (finite element and poroelastic simulations) of CO2 injection scenarios are examined to predict stress changes, deformation, and potential failure zones in the caprock and adjacent faults. Caprock suitability in the Sichuan Basin varies by structural unit; central basin areas (green) are rated highly suitable for CO2 storage, whereas southwestern fold belts (red) are deemed unsuitable. Risk factors such as caprock fracturing, fault activation, and CO2 leakage pathways are assessed in light of both field case studies (e.g., induced seismicity in the basin's southwest) and model predictions. Sensitivity analyses identify which mechanical parameters (e.g., tensile strength, friction angle, elastic modulus) most strongly affect caprock stability. Mitigation strategies – including injection pressure management, gradient control, and real-time monitoring – are discussed to ensure caprock preservation. A case study of the Longmaxi Shale is presented to contextualize these findings for one of Sichuan's primary shale formations, illustrating how its mineralogical composition and mechanical behavior inform safe CO2 injection limits. The results underscore that with careful characterization and operational controls, the Sichuan Basin's shale caprocks can maintain integrity under CO2 injection, enabling effective carbon storage. The findings have broad relevance for CCS projects in similar compressional basins worldwide.