Study on the Mechanisms of Microscopic Remaining Oil Flow During Cyclic Water Flooding

Water flooding remains the primary development method for oil fields both domestically and internationally. Currently, continued water flooding is the predominant approach. Due to reservoir heterogeneity and developed fractures, the swept volume of water flooding gradually becomes fixed (injected water primarily flows through zones with good reservoir properties, while zones with poor properties receive little). Producing crude oil in zones with poor properties is challenging. However, the oil displacement mechanism of cyclic water flooding is currently less studied. The study used microfluidic experimental methods to create flake models that represent both homogeneous and fractured reservoirs. The innovation of this method lies in its ability to conduct visual experiments on periodic water injection and study its residual oil occurrence state. It conducted remaining oil production experiments for both conventional water flooding and transient-state water flooding (also known as cyclic water flooding), which revealed the oil displacement mechanisms in heterogeneous and fracture models under transient water flooding at different pressure stages. It also identified the types of remaining oil displaced at each stage. This study confirms that under transient flooding conditions, the disturbance of the pressure field leads to effective remaining oil production in low-permeability zones and an expansion of the swept volume of water flooding. These findings can guide water flooding techniques and offer insights into the development of surfactant flooding and microbial flooding methods.