Flow and clogging characteristics of oil-water droplet clusters in a dual-porous medium with both fractures and matrix

The transport and blockage behavior of droplets in porous media is a key issue in understanding the dynamics of multiphase fluids in complex porous structures, and is crucial for predicting material transport efficiency and regulating flow. Existing literature lacks research on the dynamic behavior of droplet populations in fracture-matrix dual-porous media with significant permeability contrasts. This study designs microfluidic visualization chips with different fracture structures for fracture-matrix dual-porous media, systematically investigating the flow and clogging behavior of oil-water droplet populations. The motion characteristics of monodisperse droplet swarms within dual porous media under typical operating conditions were clearly defined. It was revealed that droplets exhibit markedly distinct flow characteristics in fractures and the matrix. Specifically, the difference in their motion velocities can reach a factor of two. An analysis was conducted on the influence of the porous media structure and the inherent properties of the droplets on the migration of the droplet swarms. The results indicate that the structural parameters of the fractures, in conjunction with the permeability differences, jointly influence the transport characteristics of the droplet swarms. The droplet sweep range and blockage probability are higher under extreme droplet-to-pore size ratios, and decrease with increasing capillary number. The highest droplet blockage volume ratio can reach approximately 85%. By analyzing phase diagrams of droplet sweep states in dual-porosity media under varying droplet-to-pore size ratios and fracture-matrix permeability differences, the critical control mechanisms governing the sweep state of droplet populations in dual-porous media are revealed. This provides a theoretical basis for fluid flow studies in dual-porous media and oilfield development.