Analysis of Caprock Mechanical Stability for CO2 Geological Storage Based on the Fuzzy Analytic Hierarchy Process

Carbon dioxide geological sequestration (CCS) technology is a key measure for addressing climate change, and its safety heavily depends on the mechanical stability of the caprock in the storage formation. This paper develops a comprehensive evaluation system based on the Fuzzy Analytic Hierarchy Process (FAHP) to assess the mechanical stability of the caprock after CO2 injection into saline aquifers. Compared to other quantitative evaluation methods, FAHP is more effective at handling the fuzziness and uncertainty inherent in the evaluation process. By utilizing a fuzzy judgment matrix, it accurately reflects the relative importance and uncertainty of various factors, thus enhancing the scientific rigor and reliability of the evaluation results. To validate the effectiveness of this evaluation system, an engineering case study was conducted using geological data from the Jilin Oilfield. The results indicate that the caprock of the Fourth Member of the Sifangtai Formation in the Jilin Oilfield, as evaluated by the FAHP model, exhibits high stability across multiple mechanical indicators, and possesses strong CO2 sequestration capacity in terms of thickness, compressive strength, shear strength, and low permeability. The evaluation result was classified as "Good, " meeting the safety requirements for CO2 sequestration. This study demonstrates the advantages of FAHP in assessing the mechanical stability of caprocks in complex geological environments and provides an effective evaluation tool and technical support for CO2 sequestration projects in the Jilin Oilfield and similar regions. In the future, integrating actual monitoring data to further optimize this evaluation system will provide more accurate decision-making support for the long-term stability prediction and risk management of CO2 sequestration.