Exploration of the storage capacity and suitability of the Ordovician saline water layer for carbon sequestration in the Huainan mining area

Against the backdrop of escalating global climate change and increasing pressure to reduce carbon emissions, carbon capture, utilization, and storage (CCUS) technologies have gained widespread attention as crucial measures to mitigate greenhouse gas emissions. Among these methods, CO₂ geological sequestration in deep saline aquifers is considered one of the most promising methods because of its extensive reservoir distribution, high storage capacity, and long-term stability. However, compared with CO₂ sequestration studies in oil and gas fields, research on CO₂ geological sequestration in deep saline aquifers within coal mining areas remains relatively insufficient, particularly regarding assessments of CO₂ storage capacity and suitability, which remain underexplored. The Huainan mining area, as a significant coal production base and energy industry center in China, possesses favorable geological characteristics and sequestration potential in its Ordovician saline aquifer. However, a systematic scientific assessment is lacking. Therefore, this study, which is based on existing geological data from the Huainan mining area, incorporates cap rock analysis to conduct a quantitative evaluation and comprehensive analysis of the CO₂ sequestration capacity and suitability of the Ordovician saline aquifer. The results indicate that the Ordovician Majiagou formation limestone saline aquifer in the Huainan mining area has a wide distribution area with high porosity and permeability. The overlying multilayer mudstone, shale, and dense sandstone cap rocks are thick with low permeability, forming an ideal storage cap rock combination and providing stable geological conditions for long-term CO₂ sequestration. Through the calculation and analysis of CO₂ residual trapping and solubility trapping mechanisms, the total sequestration capacity of the Ordovician saline aquifer in the Huainan mining area was found to be 361.1091 × 10⁵ t, with residual trapping dominating. This result is closely linked to the rapid physical process of residual trapping, whereas solubility trapping, owing to its slower chemical nature, contributes less in the short term. The CO₂ sequestration capacity is highest in the Xieqiao syncline deep structural belt, the southern wing of the Panji anticline, and the Zhuji collision structural belt. In terms of suitability evaluation, a multi-indicator assessment system based on engineering geological conditions, sequestration potential, and socioeconomic factors was constructed. The results show that the Xieqiao syncline deep structural belt, the Panji anticline south wing structural belt, and the Zhuji overthrust structural belt are rated as the most suitable sequestration areas, reflecting their superior geological suitability. The Panji anticline north wing, the Gu Gui transitional structural belt, and similar structural belts are evaluated as relatively suitable areas. In contrast, the Bagong Mountain arc-shaped monocline structural belt, the Shungeng Mountain fault block, and the Fushun fault block structural belts are rated as unsuitable for sequestration. This study systematically reveals the CO₂ geological sequestration characteristics of the Ordovician saline aquifer in the Huainan mining area from three aspects: cap rock matching, sequestration capacity evaluation, and suitability assessment. The findings provide a scientific basis for the planning and deployment of CO₂ deep saline aquifer sequestration projects in the Huainan mining area and similar regions.