Evolution law and control method of invasion front surface during the immiscible displacement in porous media: Expanding the swept volume

The invasion front evolution of immiscible fluids in porous media determines its swept volume, which is an inevitable topic faced by oil and gas field development, CO₂ geological sequestration, and underground energy storage. Characterizing the morphology of the invasion front of immiscible fluids in porous media, revealing the pore throat flow mechanism under the influence of multiple factors, and exploring efficient control methods to expand swept volume are the current and future research focuses. Here, starting from the indoor research methods of the invasion front, this paper gives a detailed review of the entire life cycle of this topic. First, the physical simulation and numerical simulation research methods were compared, and the advantages and disadvantages of three typical physical models were analyzed in detail; secondly, the invasion front type discrimination methods such as the invasion front morphology method and the fractal dimension method were introduced in detail, and the reliability of their classification results was verified; then, the influence of three major categories (fluid parameters, injection parameters and model parameters) and seven sub-factors on the evolution of the invasion front were discussed in detail, and the pore throat flow mechanism of the invasion front was explored and revealed. The continuous change diagram of pore throat flow behavior of the invasion front relative to the contact angle was summarized; thirdly, the existing LogM-LogCa classic phase diagrams were summarized and compared, and the distribution characteristics of various invasion front patterns were analyzed in combination with the main control zoning of capillary force and viscosity force; Meanwhile, other types of phase diagrams based on wettability, pore throat disorder, wall roughness and other factors were analyzed. The phase diagrams reviewed and summarized cover all influencing factors, and explain their establishment process and precautions; next, a brief analysis of the uniqueness of the gas invasion process is made based on gas gravity differences, viscosity differences, and solubility; finally, based on the above research content, a corresponding invasion front fingering control method is proposed, mainly focusing on the mechanism and application effect of the pulse injection method. Physical methods such as applied force field and electric field are a potential and clean way to suppress fingering and expand swept volume. The review content of this paper covers basic models, image processing, theoretical analysis, and technological frontier dynamics, which is suitable for researchers in related fields to conduct basic cognition and in-depth learning. In addition, the diagrams of the main controlling factors and fingering mechanisms changing with the wetting angle are two major contributions and new insights of this review. This paper plays a key guiding role in the research of improving oil and gas recovery and underground fluid storage based on expanding swept volume.