Preferential flow control in heterogeneous porous media by concentration-manipulated rheology of microgel particle suspension

Preferential flow is commonly encountered but decreases the efficiency of multiphase displacement in most industrial processes. Microgel particle suspensions with polymer/colloid duality are a potential candidate to overcome such nonuniform flow. In this study, a novel mechanism of preferential flow control in heterogeneous porous media by concentration-manipulated rheology of microgel particle suspension was proposed, which is strongly supported by microfluidic experiments and pore-scale simulations. By varying the injection concentration, displacement processes were identified to three transport modes: the channeling mode at a low injection concentration, the synchronous mode at an intermediate injection concentration, and the fluctuation mode at a high injection concentration. Concentration-manipulated rheology and nonuniform particle concentration distribution in different layers make it possible to realize uniform flow in heterogeneous porous media. It was demonstrated that the multiphase processes at low/intermediate injection concentrations are dominated by two-phase flow with particle advection-diffusion in the invading phase but that at high injection concentrations disobeys this model due to local particle rapid enrichment by particles lagging behind the displacing fluid. During the displacement process, an intermediate injection concentration always exhibits the optimal synchronous displacement by self-adaptive concentration manipulation in different layers. However, concentration manipulation at low injection concentrations was too weak to suppress preferential flow, and a high injection concentration was sensitive enough to alternate preferential flow pathways frequently, which will lead to oleic ganglia being trapped. These findings deepen the understanding of microgel particle suspension dynamics in heterogeneous porous media and shed unique insights for their applications, such as enhanced oil recovery and CO2 sequestration.