Numerical Simulation of CO2 Injection and Production in Shale Oil Reservoirs with Radial Borehole Fracturing

Shale oil is a vital strategic resource in China. Developing shale oil using CO2 not only enhances oil recovery but also contributes to achieving Chinese “dual carbon” goals. Given the challenges of insufficient number of fractures, inadequate vertical stimulation volume, and poor reservoir mobility associated with horizontal well fracturing, this study proposes a method for CO2 flooding based on radial borehole fracturing in a single well to achieve long-term carbon sequestration. To this end, a multi-component numerical model is built to analyze the production capacity of radial borehole fracturing. This study analyzed the impacts of non-Darcy flow, diffusion, and adsorption mechanisms on CO2 migration and sequestration. It also compared the applicability of continuous CO2 flooding and CO2 huff-and-puff under different matrix permeabilities. The results indicate that (1) CO2 flooding using radial borehole fracturing can achieve long-term oil production and carbon sequestration. (2) Under low permeability conditions, the liquid non-Darcy effect retards the flow of oil and CO2, while diffusion and adsorption facilitate CO2 sequestration in the reservoir. The impact on carbon sequestration is ranked as follows: non-Darcy effect > adsorption > diffusion. (3) High-permeability reservoirs are more suitable for carbon sequestration and should utilize continuous CO2 flooding. For low-permeability reservoirs (<0.001 mD), huff-and-puff should be employed to mobilize the reservoir around fractures and achieve carbon sequestration. The findings of this study are expected to provide new methods and a theoretical basis for efficient and economical carbon sequestration in shale oil reservoirs.