Geothermal Exploitation via Recycling Supercritical CO2 after Thermal Recovery in Deep Heavy Oil Reservoirs

Abstract

Abstract After thermal flooding, the natural elastic energy of deep heavy oil reservoir tends to deplete. Yet, this reservoir retains plenty of remaining heat and oil. Supercritical CO2 (SCCO2) emerges as an optimal heat-carrying fluid and enhances heavy oil extraction due to its high mobility and unique thermal properties. In this work, a comprehensive model of geothermal exploitation for depleted deep heavy oil reservoir via SCCO2 injection was established, in which the process of heavy oil extraction, asphaltene precipitation on permeability were incorporated. Core displacements and computed tomography (CT) were employed to obtain the variational values of asphaltene precipitation caused by SCCO2 on permeability. A reservoir simulation software (STARS), using the above various parameters such as diffusion coefficient of CO2, permeability parameter and heat transfer properties, simulates the process of SCCO2 injection for geothermal exploitation and remaining heavy oil development. SCCO2 with remarkable diffusivity and fluidity facilitates heavy oil extraction and obtain heat energy in a wider area. Consequently, the average oil recovery evidently rises from 18.5% to 30.8%. Nevertheless, the stability of heavy oil's micellar structure is compromised by SCCO2, resulting in the aggregation and adsorption of asphaltenes onto the rock surface to promote the formation of membrane oil and reduce the effective flow area. The difference in gas-phase permeability between the core without steam flooding and the core subjected to steam flooding after SCCO2 flooding averages 7.2%. In the case of high remaining oil saturation in the depleted deep heavy oil reservoir, the backflow of SCCO2 propelled by gravity and capillary force leads to the extraction of numerous light components, leaving behind asphaltene precipitation. This process reduces the consumption of SCCO2 in the lower-temperature region. Subsequently, the swift entry of SCCO2 into regions with low oil saturation, facilitating efficient utilization of steam waste heat and formation heat. SCCO2 exhibits the potential to enhance oil recovery in low-temperature regions and improve the heat mining rate in high-temperature regions in deep heavy oil reservoirs. The mathematical and experimental simulations offer unique and reliable insights for the advancement of depleted deep heavy oil reservoirs.