Effect of CO2 Huff-n-Puff Mode with a Horizontal Well on Shale Oil Recovery: A Three-Dimensional Experimental Study

After conventional development, thereis still a significant amountof residual oil as a result of the poor porosity and permeabilitycharacteristics of shale reservoirs. Although CO2 floodingis one of the most reasonable recovery techniques, it is affectedby a serious sweep efficiency issue. In this paper, six CO2 huff-n-puff cooperative combination methods were established withthe aid of three-dimensional physical simulation equipment, includingCO(2) huff-n-puff (HNP), water-disturbance-assisted CO2 huff-n-puff (WD-HNP), surfactant- and water-disturbance-assistedCO(2) huff-n-puff (SWD-HNP), pumping-production-assistedCO(2) huff-n-puff (PP-HNP), water-disturbance-assisted CO2 huff-n-puff after pumping production (WDP-HNP), and surfactant-and water-disturbance-assisted CO2 huff-n-puff after pumpingproduction (SWDP-HNP). The displacement characteristics, utilizationlaw, and development effect were investigated. CO2 huff-n-puffrequires more gas injection quickly, and low permeability and pressuredifference can easily cause irregular gas channeling, showing thearc linear flooding pattern. Water disturbance can significantly delaythe rapid breakthrough, so that the displacement edge shows the radialflooding pattern. The effect of pumping production on the displacementis not obvious, and the leading edge still shows an oval-shaped floodingpattern. Surfactant assistance improves the gas injection ability,eventually demonstrating a plane steady flooding pattern. In comparisonto HNP, the average enhancement degree of water injection disturbance,pumping production, and surfactant assistance to the utilization extentis 6.61, 1.82, and 8.93% respectively. Meanwhile, SWDP-HNP had thehighest oil recovery (33.35%) among all modes. By comparison of effectiveproductivity, it revealed that about 12% of the lifting range is helpedby surfactant assistance, followed by a water injection disturbancelifting amplitude of 5.5%, while pumping production only led to a3% improvement. With the combination of all development effect evaluationindicators, SWD-HNP is a reasonable displacement method to improveshale reservoir recovery in this study.