Abstract: In the context of the global carbon neutrality strategy, the continuous increase of greenhouse gas emissions, mainly CO₂, has adversely affected the global climate, ecosystem and human life. CO₂ geological storage is an important technical means to achieve the goal of carbon neutrality. As the sealing barrier of potential storage structure, the sealing property of caprock is the key to long-term or even permanent CO₂ storage. The salt-gypsum caprock has the excellent characteristics of "low porosity and low permeability", "good stability" and "high breakthrough pressure", which can be used as a caprock for long-term safe storage of CO₂. However, the physical and chemical properties of the salt-gypsum caprock are quite different from those of other lithological caprocks, which leads to the challenge of CO₂ storage sealing evaluation of salt-gypsum caprock. It is urgent to establish a CO₂ storage sealing evaluation method suitable for salt-gypsum caprock. Therefore, based on the Analytic Hierarchy Process (AHP), this paper comprehensively considers the key factors affecting the sealing performance of the caprock, such as the macro indicators, micro indicators and breakthrough pressure, and establishes the evaluation index system of CO₂ sealing performance of the salt-gypsum caprock, and divides the four advantages and disadvantages of different indicators, and obtains the influence weight of each index on the sealing performance of the salt-gypsum caprock. Secondly, combined with the comprehensive evaluation method of fuzzy mathematics, the total weight of CO₂ storage sealing evaluation of salt-gypsum caprock is calculated, and a comprehensive evaluation method of CO₂ storage sealing suitable for salt-gypsum caprock is formed. Finally, taking Gaoshiti Moxi block in Sichuan Basin as an example, the CO₂ storage and sealing ability of this potentially depleted gas reservoir caprock is systematically evaluated. It is found that the total weight of the seal evaluation of Gaoshiti Moxi structural gas reservoir caprock is [2.5,3.0], and the evaluation grade is "better", which has good CO₂ storage ability and is suitable for the application of CCS (carbon capture and storage) technology in the future. The research results of this paper can provide some technical guidance for CO₂ storage site selection and storage safety evaluation of the depleted gas reservoir caprock.

Key words: Sichuan Basin, depleted gas reservoir, salt-gypsum caprocks, CO₂ storage, sealing evaluation