Evaluation of CO2 utilization and storage potential in the Jimsar shale play from an optimization study

CO2-based enhanced oil recovery (EOR) methods have been widely used in conventional reservoirs, which is also attractive to sequestrating CO2 underground. However, the existing studies on EOR and CO2 sequestration are separate, and there is still a lack of integrated assessment of the carbon capture, utilization, and storage (CCUS) potential of shale reservoirs. In this paper, huff-n-puff (HNP) is considered to be a suitable method for introducing CO2 into the shale formation, and a co-optimization study of EOR and carbon storage is carried out. A fluid model was first developed to simulate the physical change of CO2 and shale oil under reservoir conditions. After that, a numerical simulation model of the injection well is established and calibrated based on the field production history. Finally, a novel optimization method of huff-n-puff with stimulated reservoir volume (SRV) pressure as the criterion is proposed, and the CCUS potential was further investigated. The simulation results show that the optimal recovery can be increased by 10% after 1560 days of huff-n-puff compared to primary depletion. Due to the unique recovery method, 27%–70% of the injected CO2 was trapped during the HNP process, and the proportion of free gas increased with the reservoir pressure, while most of the trapped CO2 was dissolved in the shale oil. Furthermore, an economic analysis with consideration of oil price and the carbon tax was also performed. The oil price directly determines whether CO2 HNP injection is feasible while the carbon tax influences the choice of development scenarios. If the carbon tax is higher than 40$/t, a scenario with more CO2 sequestered is preferred. The investigation performed in this study provides theoretical support for CO2 sequestration in shale reservoirs and a reference for carbon tax policy formulation.