Characterization of Pore Structure and Water-Driven Residual Oil Distribution in Low-Permeability Reservoirs Based on Digital Cores

In order to solve the problems of unclear mechanism of residual oil formation and storage state at the late stage of water-driven development in low-permeability sandstone reservoirs, a three-dimensional digital core model was constructed based on CT scanning technology. A three-dimensional digital core model of the reservoir was constructed based on CT scanning technology, and an unstructured tetrahedral mesh model was established to extract the connected pore structure and quantitatively characterize the micro-pore structure of the rock samples. A mathematical model of oil-water two-phase microscopic seepage flow was established based on NS equation and level set algorithm, and a finite element method was used to solve the model and simulate the microscopic water-driven oil flow. The results show that: the pore throat size and connectivity are the main factors determining the permeability of the reservoir; obvious viscous fingering phenomenon can be observed in the simulation of microscopic water-driven oil, and the residual oil of the water-driven oil mainly exists in the form of reticulated residual oil, blind-end pore residual oil, residual oil in small pore throats, residual oil in the parallel channels, and oil film; increasing the intensity of the injection can effectively utilize the reticulated residual oil and the residual oil in small pore throats, and the improvement of the viscosity ratio can obtain a larger wave and oil-water ratio, which can be used to improve the oilwater flow. Improvement of viscosity ratio can obtain larger wave and volume, and improvement of wettability can effectively utilize the remaining oil in the blind-end pores and oleophilic pore channels.