Mechanism of CO2 Enhanced Reverse Hydraulic Assisted Oil Displacement to Improve Recovery and Sequestration Ratio in Tight Reservoirs

Tight reservoirs are usually developed using horizontal well volume fracturing, but this method has problems such as rapid decline in production and low initial recovery. Therefore, there is an urgent need to explore new technologies to improve recovery. Hydraulic fracturing assisted oil displacement and CO2 flooding have been proven to significantly improve the recovery of tight reservoirs, but these technologies are currently mostly applied independently, and no systematic integrated research has been conducted. The paper proposes for the first time the application of CO2 enhanced reverse hydraulic fracturing assisted oil displacement to tight reservoirs. Through the use of magnetic resonance imaging equipment, CO2 enhanced reverse hydraulic fracturing assisted oil displacements are conducted to quantify the contribution of recovery and CO2 sequestration ratio at different stages, clarify the degree of mobilization of crude oil in microscopic pores, and reveal the evolution patterns of oil saturation and flow distance under different injection conditions. The results indicate that the oil recovery of CO2 enhanced reverse hydraulic fracturing assisted oil displacement can reach 88.8%, with contributions of 12.3% from fracturing fluid imbibition, 73.2% from CO2 flooding, and 3.3% from dissolved gas drive. The CO2 sequestration ratio is 65.5%. Compared with conventional CO2 flooding, under the same the injection volume, CO2 enhanced reverse hydraulic fracturing assisted oil displacement has a slower forward propagation speed but a wider coverage range and higher CO2 utilization efficiency. After CO2 flooding, the depletion of driving energy and CO2 breakthrough can easily cause residual oil enrichment at the production end. However, CO2 enhanced reverse hydraulic fracturing assisted oil displacement improves the residual oil enrichment production end through synergistic mechanism such as fracturing energy replenishment, fracturing fluid imbibition, and high-pressure mixed-phase flooding. In addition, compared with water injection huff and puff, CO2 injection huff and puff, and conventional CO2 flooding, CO2 enhanced reverse hydraulic fracturing assisted oil displacement increased the recovery by 16.7% to 75%. The results of this investigation provide a theoretical basis for the field application of CO2 enhanced reverse hydraulic fracturing assisted oil displacement in tight reservoirs.