Experimental and Numerical Simulation Study on the Influence of Fracture Distribution on Gas Channeling in Ultralow-Permeability Reservoirs

Abstract

Fracture development in ultralow-permeability reservoirs results in gas channeling and lower oil recovery during CO2 flooding. In this study, the physical properties of a light oil-CO2 system were experimented, the physical properties subsequently simulated, and the effects of fracture distribution on gas channeling analyzed using the fracture mechanism model. Then, a geological reservoir model with added hydraulic fractures was used to predict CO2 injection. It is shown that gas channeling time was affected by the fracture angle and the distance between the production well fracture and injection well fracture. First, set Y (north) direction as 0°, keep the angle of the production well fracture unchanged, and only change the angle of the injection well fracture. In this case, a smaller angle of the gas injection well fracture resulted in more gas sweep area and gas channeling more delayed. Second, keep the injection well fracture angle constant and only change the angle of the production well fracture; in this regard, two cases are considered. The one is when the injection well fracture angle is smaller than 45°; in this case, the effect of distance between the production and injection fractures is more than production pressure difference, the distance between the production and injection fractures is greater, the gas sweep area is larger, and the gas channeling is later. The other is when the injection well fracture angle is greater than 45°, which results in a closer distance between the production well and injection well fractures and affects the gas channeling less than the production pressure difference. Third, the angle between the gas flooding direction (along X) and the production well fracture is greater, the production pressure difference is more homogeneous, and the gas channeling is later. In the geological model without connected fractures, CO2 flooding achieved gas channeling all over the study area after 7.5 years under the effect of distance between the production and injection fractures and the production pressure difference. The cumulative oil increase is 2.32 millon standard barrel (MSTB) after 20 years.