Influence of Heterogeneity and Fracture Conductivity on Supercritical CO₂ Miscible Flooding Enhancing Oil Recovery and Gas Channeling in Tight Oil Reservoirs

Abstract

Aiming to investigate the supercritical CO2 miscible flooding performance in heterogeneous reservoirs, the CO2 gas channeling experiments of parallel short cores (matrix) with different permeability ratios and parallel long cores with different fracture conductivities were carried out in this work. The influences of the permeability ratio and fracture conductivity on oil recovery and gas channeling were analyzed. The results show that reservoir heterogeneity plays a key role in enhancing oil recovery. The permeability ratio not only affects the oil output but also controls the gas breakout time and the oil production in the post-breakout stage. High-permeability cores have higher displacement efficiency than low-permeability cores, but gas breakthrough occurs earlier. The formation of dominant gas channels in high-permeability cores restricts the flow of CO2 into low-permeability cores, resulting in lower displacement efficiency of low-permeability cores. In the case of the existence of fractures, a rapid breakthrough of CO2 will occur, and as the conductivity of the fractures increases, the gas breakthrough time becomes shorter and the gas channeling in the fractures becomes more serious. When the fracture–matrix core permeability ratio reaches 37, the matrix core does not produce oil and gas. In the initial stage, as the fracture conductivity becomes stronger, the oil production rate becomes faster and most of the oil is recovered before gas breakthrough. The fractures are not only the channel of oil flow but also the main path of gas channeling. The recovery curve flattens out rapidly after CO2 breakthrough. As fracture conductivity increases, the recovery curve flattens out faster, resulting in poor ultimate recovery. This study is expected to provide theoretical guidance for miscible CO2 flooding in heterogeneous tight oil reservoirs.