Geothermal Exploitation Achieved by Injection of Supercritical CO2 Into Deep Heavy Oil

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 24483, “Geothermal Exploitation Through Recycling Supercritical CO2 After Thermal Recovery in Deep Heavy Oil Reservoirs,” by Yu Li, China University of Petroleum and National University of Singapore, and Chao Peng and Waleed Ali Khan, China University of Petroleum, et al. The paper has not been peer reviewed. Copyright 2024 International Petroleum Technology Conference. _ After thermal flooding, deep heavy oil reservoirs retain plenty of heat and oil. Supercritical CO2 (SCCO2) emerges as an optimal heat-carrying fluid and enhances heavy oil extraction because of its high mobility and unique thermal properties. A comprehensive model of geothermal exploitation for depleted deep heavy oil reservoirs using SCCO2 injection is described in the complete paper. SCCO2 Potential in Geothermal Exploitation In recent years, the development of many deep heavy oil reservoirs has been completed using steam huff ’n’ puff. However, the substantial contrast in physical properties between steam and heavy oil intensifies the occurrence of viscous fingering. After steam huff ’n’ puff, plenty of thermal energy is trapped at the interface of the steam chamber, resulting in less heat loss (Fig. 1). Because of the high temperature of the deep reservoir, such regions have great geothermal potential. CO2, as an efficient and safe heat-carrying fluid, can be used in geothermal exploration. In deep heavy oil reservoirs with high temperature and pressure, CO2 enters the supercritical state. SCCO2 has a viscosity close to gaseous CO2 and the heat capacity of liquid CO2. In addition, SCCO2 exhibits higher solubility in heavy oil reservoirs. Despite these characteristics, SCCO2 has a pronounced extraction effect on light components and promotes the precipitation of asphaltene. Consequently, the extracting process diminishes the permeability of porous media. To assess the suitability of CO2 and water for geothermal exploration in depleted deep heavy oil reservoirs, it is imperative to calculate and compare the heat-mining rate under elevated temperature and pressure. Experimental and Simulation Methods Apparatus and Method. Standard core models were used to simulate petrophysics under high temperature and backpressure. The rock samples were from Yutian West Block, Lukeqin, and the target reservoir was at a depth of more than 3000 m. Based on core models with different permeabilities, four displacement experiments were designed to investigate permeability alteration affected by steam and CO2 flooding. The displacement experiment steps were as follows: 1. The core model was placed inside the temperature and pressure resistance core vessel to finalize the construction of the experimental setup. Then, the permeability of the core was measured by gas measurement under high temperature and pressure. 2. The temperature and pressure resistance of the core vessel were maintained at 120°C and 30 MPa, respectively, to complete the brine-saturation process. 3. Heavy oil was injected at a constant rate of 0.25 mL/min to complete the heavy oil saturation process; aging time was greater than 72 hours. 4. Steam (250°C) was injected at a constant rate of 0.5 mL/min to extract heavy oil from the core model until steam breakthrough at the outlet port occurred. 5. SCCO2 was injected at a constant rate to further extract heavy oil. SCCO2 was injected quantitatively under different scenarios, with varying injection speeds and volumes. Flow rates of 0.1, 0.5, and 2.5 mL/min were used. 6. The permeability of the core gas was measured at every testing node.