CO₂ geological storage combined with deep saline water recovery technology (CO₂-EWR) is one of the most effective ways to reduce carbon emissions. Due to the complex structural features, it is difficult to use CO₂-EWR technology in Huaiyin Sag, Subei basin, East China. In this study, the multi-source information superposition evaluation technology of GIS was utilized for the selection of CO₂ storage sites and water displacement potential target areas in this area, which mainly focused on the sandstone reservoirs of Cretaceous Pukou Formation. Based on the results, a three-dimensional injection–extraction model was established. Various scenarios with different production/injection well ratios (PIR) were simulated. Research has shown that the suitability of the surrounding site of Huaiyin Power Plant can be divided into two levels: relatively suitable and generally suitable; the area in the generally suitable level accounts for more than 80%. At a PIR of 1, CO₂ is distributed asymmetrically, whereas at PIRs of 2 or 4, CO₂ is distributed symmetrically. When the number of production wells is constant, a higher injection rate results in a faster expansion rate of the CO₂ plume. This means that the time taken for the CO₂ plume to reach the production wells is shorter. Reservoir pressure increases rapidly after more than 60 years of CO₂ injection at lower PIR values, while at higher PIRs, reservoir pressure eventually stabilizes. Higher PIR values correspond to higher gas saturation, indicating a greater capacity for CO₂ sequestration with more producing wells. When PIR = 4, the total CO₂ injection increased by 55.73% compared to PIR = 1. However, the extraction of saline decreases with an increase in the number of producing wells, resulting in a decrease in replacement efficiency. This study provides a theoretical basis and technical support for the implementation of large-scale CO₂-EWR engineering and technology demonstration in this region.

Introduction: The volumetric method is the primary approach for calculating geological CO ₂ storage potential, with its accuracy largely dependent on the pore volume of reservoir rocks and the effective storage coefficient. While the precision of reservoir rock pore volume can be enhanced through more sophisticated geological exploration techniques, the current selection of effective storage coefficients lacks a theoretical foundation. Thus, obtaining a more accurate effective storage coefficient is crucial for improving the evaluation precision of CO ₂ geological storage potential. Methods: To explore the factors influencing the effective carbon sequestration coefficient in saline aquifers and accurately assess their storage potential, nine sets of multiphase flow core displacement experiments were conducted using orthogonal design, with porosity, confining pressure, and pressure difference as variables. Results: The results indicate that among these three factors, porosity has the most significant impact on maximum residual CO ₂ saturation. Discussion: Qualitative analysis of water migration in cores during displacement was performed using nuclear magnetic resonance (NMR) T ₂ curves, revealing a close correlation between water movement and pore structure: water in mesopores and macropores is preferentially displaced, whereas water in nanopores and micropores is more resistant to displacement. Additionally, NMR was employed to analyze the maximum residual CO ₂ saturation of artificial cores under different conditions, leading to the establishment of a multiple linear regression equation for maximum residual CO ₂ saturation. By incorporating the volume coefficient derived from numerical simulations, the geological CO ₂ storage coefficient for actual engineering sites can be estimated.

As a bottom technology for CO₂ reduction, geological CO₂ storage has attracted great attention from geologists, but there are few reports on the research of the caprock self-sealing effect due to CO₂ leakage. Ping’an is a natural CO₂ leakage site, which can be compared to the leakage scenarios of geological CO₂ storage. Based on the water quality test results and geological observation data, the numerical simulation of geochemistry is carried out. The results show that: First, gypsum dissolves and calcite precipitates during the migration of CO₂-rich water to the surface. This process presents a self-sealing effect, and the closer to the surface, the more obvious the self-sealing; Second, the self-sealing effect is formed rapidly. For a 30 cm wide fissure, it only takes a few hundred days to achieve self-sealing; Third, the CO2 leakage was estimated, about 140,813.3 m³, or about 251.28 tons for 1 m long fissure.