Effect of Fracture-Matrix Interaction on CO<sub>2</sub>-Oil Displacement via Dual-Permeability Microfluidics
Zheng Cheng, Y J Li, Chenyue Xie, Feng Du, Hui Zhao, Xiaolong Yin, Jingwei Huang
Abstract
Fractured shale reservoirs pose a major challenge for CO 2 -enhanced oil recovery (CO 2 -EOR) due to the complex interaction between high-permeability fractures and the low-permeability matrix. To better understand the mechanisms of the CO 2 -oil displacement in fractured shale, we conducted microfluidic experiments in a dual-permeability chip. We examined how the pressure difference and phase conditions affect the CO 2 -oil displacement efficiency and residual oil. Under immiscible conditions, a critical differential pressure was required for the CO 2 to penetrate the matrix. Below this threshold, only oil in the fracture can be recovered. Increasing differential pressure enhanced both the sweep depth of CO 2 and the ultimate recovery of oil. Conversely, under miscible conditions, efficient molecular diffusion allows CO 2 to readily penetrate the matrix even at low pressure differentials, achieving a 27.88% higher ultimate recovery compared with immiscible displacement at a Δ P of 0.10 MPa. Three typical types of residual oil were discovered in the matrix, including clustered, columnar, and filmy. Clustered and columnar oils account for the majority of residual oil in the matrix, while filmy oil increases with pressure differences. This work directly visualizes and quantifies how the interplay of pressure, miscibility, and capillary forces at the fracture-matrix interface governs displacement efficiency, providing a fundamental framework for optimizing the CO 2 -EOR strategies in fractured reservoirs.