Volume 38: Energy Transitions toward Carbon Neutrality: Part I

Experimental investigation of CO2 flooding in tight oil reservoirs: Effects of the fracture aperture on production characteristics and oil distribution Mingyang Yang, Shijun Huang, Fenglan Zhao, Haoyue Sun, Xinyang Chen, Xinhan Fan

Abstract

Field observations, along with experimental laboratory, exhibit evidence that gas injection in tight oil reservoirs is technically feasible. However, there is a lack of understanding the effects of fracture aperture on the oil production behaviors, especially when the fracture aperture is less than 50μm. In this study, CO2 flooding experiments were carried out using different fracture aperture core samples considering the confining pressure (11μm, 15μm, 20μm, 25μm). And the production characteristics and remaining oil distribution were evaluated based on nuclear magnetic resonance (NMR). The results showed that fracture aperture is of significance to the permeability. Specifically, with the increase of fracture aperture, permeability increases in power law while porosity increases linearly. It is worth noting that the recovery of CO2 flooding is the highest (17.60%) after water flooding when the fracture aperture is 20μm. Moreover, the dissolution diffusion mechanism becomes more obvious when the fracture aperture increases (10~20μm), but gas channeling will lead to a large amount of remaining oil when the fracture aperture exceeds a certain limit (20~25μm) according to the results of nuclear Magnetic Resonance Imaging (MRI). The results provide a theoretical basis for further understanding the effect of fracture aperture on CO2 injection in tight reservoirs.

Keywords tight oil reservoirs, CO2 flooding, fracture aperture, production characteristics, oil distribution