Pore Scale Modeling of Capillary Action in Determining Oil–Water Flowing by Water Flooding: A Case Study of Low-Permeability Sandstone in the Ordos Basin, Northern China

Abstract

Abstract Capillary action plays an important role in oil recovery by water flooding. As the pore channel radius decreases, the capillary action increases, which seriously affects reservoir development, especially in a low-permeability sandstone reservoir. The Ordos Basin is a typical low-permeability sandstone reservoir in China. Studying how variations in the capillary force affect the remaining oil production on the pore scale helps in understanding how the capillary action improves the development of unconventional reservoirs. In this study, the core of the Chang 6 Formation in the Ansai Oilfield, Ordos Basin was scanned by computed tomography. Then, the digital core model was established. The oil–water two-phase flow in pores was described using the method based on the Navier–Stokes equation coupled with the method of the volume of fluid simulation. The water flooding process was simulated on the pore scale. The results show that in the process of pore scale water flooding, the oil–water interface stays at the position between the throat channel and the pore area, where the oil–water interface reverses and the capillary force presents resistance, forming the capillary barrier or capillary valve. Affected by the capillary barrier, the oil–water two-phase flow in the process of water flooding is described by a “step-by-step” model. The pore structure characteristics at the junction of the pore area and the throat channel control the movement of the oil–water interface and affect the water flooding production and the ultimate recovery factor. As the liquid injection rate increases, the oil on both sides of the main channel is produced. While the oil recovery rate reaches 66%, the remaining oil on the edges becomes increasingly difficult to be produced. This difficulty is closely related to the viscosity of the injection fluid, interfacial tension, injection rate, pore radius, and pore wall wettability.