Molecular Dynamics Insight into the CO2 Flooding Mechanism in Wedge-Shaped Pores
Lu Wang, Weifeng Lyu, Zemin Ji, Lu Wang, Sen Liu, Hongxu Fang, Xiaokun Yue, Shuxian Wei, Siyuan Liu, Zhaojie Wang, Xiaoqing Lü
Abstract
Because of the growing demand for energy, oil extraction under complicated geological conditions is increasing. Herein, oil displacement by CO2 in wedge-shaped pores was investigated by molecular dynamics simulation. The results showed that, for both single and double wedge-shaped models, pore Ⅱ (pore size from 3 to 8 nm) exhibited a better CO2 flooding ability than pore Ⅰ (pore size from 8 to 3 nm). Compared with slit-shaped pores (3 and 8 nm), the overall oil displacement efficiency followed the sequence of 8 nm > double pore Ⅱ > single pore Ⅱ > 3 nm > double pore Ⅰ > single pore Ⅰ, which confirmed that the exits of the wedge-shaped pores had determinant effects on CO2 enhanced oil recovery over their entrances. “Oil/CO2 inter-pore migration” and “siphoning” phenomena occurred in wedge-shaped double pores by comparing the volumes of oil/CO2 and the center of mass. The results of the interaction and radial distribution function analyses indicate that the wide inlet and outlet had a larger CO2−oil contact surface, better phase miscibility, higher interaction, and faster displacement. These findings clarify the CO2 flooding mechanisms in wedge-shaped pores and provide a scientific basis for the practical applications of CO2 flooding.