Experimental Study on Polymer flooding-assisted CO2-based Cyclic Solvent Injection Process for Enhancing Oil Recovery in Heavy Oil Reservoirs

Abstract

CO2-based cyclic solvent injection (CSI) process is widely applied for enhancing heavy oil recovery in petroleum industry. However, the rapid decrease in oil production after 2 or 3 cycles will be encountered in previous CO2-based CSI research due to the reduction in oil saturation near the producer. Therefore, five groups of experiments were conducted using a 1D sand-pack model to explore the EOR potential in CO2-based CSI process via polymer injection assistance to increase oil saturation around the producer. Two polymer flooding assistance modes were investigated, including injection after every cycle and injection after the cycle when oil recovery factor is less than 1%. Two slug size of polymer flooding assistance were evaluated, including volume of 1 PV and the volume of total liquid produced in the previous CO2-based CSI process. Three different concentration of polymer solution, 0ppm, 250ppm and 1000ppm, were also studied. The experimental results show that the oil recovery factor is significantly improved after polymer flooding assistance during the CO2-based CSI process. The polymer flooding assistance effectively push the remaining oil toward the producer and form an oil bank for the following CO2-based CSI section, increasing the oil saturation near the producer. The highest recovery factor (70.72%) is achieved in polymer flooding-assisted CO2-based CSI process when polymer (1000 ppm concentration) was injected after the cycle that oil recovery factor is less than 1%, and the slug size equals to the volume of total liquid produced in the previous CO2-based CSI section. The economy evaluation results show the assistance mode of conducting 1000ppm polymer flooding assistance after each cycle has the lowest material cost. Moreover, a field application of this novel technique was designed and implemented in eastern China, and a significant increase in daily oil production and decrease in water cut were achieved. In conclusion, this work innovatively combines the CO2-based CSI process with polymer flooding, and a polymer flooding-assisted CO2-based CSI technology for heavy oil reservoirs is proposed. Experimental results in both the laboratory and field reveals the excellent EOR potential and economic benefit of this novel technology for heavy oil reservoirs.