Potential CO₂ Geological Storage in Deep Tight Sandstone Saline Aquifers of Ordos Basin in China

Deep saline aquifers have significant potential for CO2 geological storage. The Longdong region, a major coal-fired power base on the southwestern margin of the Ordos Basin, faces an urgent need for CO2 geological storage. This study investigates the Permian (P) and Triassic (T) strata to assess the suitability and potentiality of deep, tight saline sandstone aquifers for CO2 storage in the study region. A multilevel suitability evaluation index system consisting of 3 primary categories, 9 subcategories, and 29 parameters was established to screen favorable reservoir intervals in deep tight sandstone saline aquifers. Furthermore, the evaluation methodology for the favorable interval selection based on the Analytic Hierarchy Process (AHP) and Fuzzy Comprehensive Evaluation method (FCE) was proposed. Seven potential reservoir-caprock assemblages (units T1–T7) were identified within the Zhifang, Heshanggou, Liujiagou, and Shiqianfeng formations. The evaluation results classify two assemblages as Class I favorable reservoir intervals, two as Class II relatively favorable, and three as Class III moderately favorable. Units T4 and T5 were identified as the Class I storage targets due to their high porosity and permeability, substantial thickness, moderate burial depth, and well-developed caprock continuity. Using the mechanism-based method of CO2 geological storage, we calculated the CO2 storage capacity of different units was calculated. The total theoretical CO2 storage capacity in the study region is estimated to reach as high as approximately 78 833.86 Mt with an effective storage capacity of 1892.01 Mt. Class I reservoir intervals account for 34 761.66 Mt theoretical and 834.28 Mt effective capacity, representing 44.10% of the total storage capacity.