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

Abstract

After conventional development, there is still a significant amount of residual oil as a result of the poor porosity and permeability characteristics of shale reservoirs. Although CO2 flooding is one of the most reasonable recovery techniques, it is affected by a serious sweep efficiency issue. In this paper, six CO2 huff-n-puff cooperative combination methods were established with the aid of three-dimensional physical simulation equipment, including CO2 huff-n-puff (HNP), water-disturbance-assisted CO2 huff-n-puff (WD-HNP), surfactant- and water-disturbance-assisted CO2 huff-n-puff (SWD-HNP), pumping-production-assisted CO2 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 pumping production (SWDP-HNP). The displacement characteristics, utilization law, and development effect were investigated. CO2 huff-n-puff requires more gas injection quickly, and low permeability and pressure difference can easily cause irregular gas channeling, showing the arc linear flooding pattern. Water disturbance can significantly delay the rapid breakthrough, so that the displacement edge shows the radial flooding pattern. The effect of pumping production on the displacement is not obvious, and the leading edge still shows an oval-shaped flooding pattern. Surfactant assistance improves the gas injection ability, eventually demonstrating a plane steady flooding pattern. In comparison to HNP, the average enhancement degree of water injection disturbance, pumping production, and surfactant assistance to the utilization extent is 6.61, 1.82, and 8.93% respectively. Meanwhile, SWDP-HNP had the highest oil recovery (33.35%) among all modes. By comparison of effective productivity, it revealed that about 12% of the lifting range is helped by surfactant assistance, followed by a water injection disturbance lifting amplitude of 5.5%, while pumping production only led to a 3% improvement. With the combination of all development effect evaluation indicators, SWD-HNP is a reasonable displacement method to improve shale reservoir recovery in this study.