CO2 Injection Capacity Estimation by Considering Salting-Out Effect: Coupled Impacts of Layered Heterogeneity and Salinity

Abstract One of the most critical factors in geological CO2 storage (GCS) is the capacity for CO2 injection. This is reduced when the salting-out effect occurs during CO2 injection. This study aims at understanding the influence of the salting-out effect on CO2 injection capacity due to salinity and layered heterogeneity. The Shenhua carbon capture and storage (CCS) demonstration project was used as a case study in which 25 scenarios were simulated. It was found that both salinity and layered heterogeneity significantly impact the salting-out effect, thereby affecting CO2 injection capacity. Higher salinity promotes the precipitation of solid salts around the injection well and reduces CO2 injection; that is, increased salinity accelerates the solid salting-out effect (i.e., mass of precipitated solid salts or solid saturation) and reduces the CO2 injection rates, thus lowering the CO2 injection capacity. Different rhythms cause variation in the CO2 injection capacity. For saturated salinity, the solid mass and injected CO2 amount for homogeneous rhythm (HR) conditions are greater when a positive rhythm (PR) of 0.4 exceeds the reverse rhythm (RR) of 0.4 and when PR 0.8 > RR 0.8 after 20 years of injection. Correspondingly, the solid saturation near the injection well exhibits the following trend: PR > HR > RR. The solid mass ranges from 6.04 × 102 kg (PR 0.8, salinity 0.03) to 60.1 (HR, saturated salinity) × 102 kg. The injected CO2 amount is between 1.2249 and 2.2860 × 108 kg. Thus, when assessing CO2 injection capacity, it is essential that the salting-out effect is not overlooked, and the factors of brine salinity and the layered heterogeneity of reservoir should also be considered. This study provides valuable guidance for site selection and optimization strategies for injection schemes related to CO2 capacities within the Ordos Basin and similar fields.