Immiscible flow-driven deformation in porous granular media

Abstract

Flow injection can induce the mechanical deformation in porous media by changing the internal pore fluid pressure. Such flow-driven deformation occurs in a wide range of applications, including transport in brain tissues, fuel cells, and in many geotechnical practices, such as geological carbon storage, gas hydrate dissociation, and hydrocarbon recovery. This hydromechanical behavior is highly related to fluid recovery efficiency and fluid storage capacity, and more than two immiscible fluids are typically involved. Pore-scale mechanism of the deformation caused by immiscible fluid injection in deformable porous media remains poorly clarified. The objectives of this dissertation are (a) to elucidate the mechanism of flow-driven deformation in deformable porous granular media at a pore scale while varying the injection and boundary conditions, (b) to develop a hydro-mechanically coupled pore network model, (c) to identify the dimensionless parameters in mapping and predicting the occurrence of flow-driven deformation, and finally (d) to further explore the effect of concurrent pore clogging with fluid flows on deformation in sandy sediments. The experimental study using a modified Hele-Shaw cell enables clear observation of mechanical deformation by the viscous fluid injection in deformable media. High capillarity and/or viscosity drag causes a greater extent of flow-driven deformation though the immiscible fluid invasion pattern differs with the capillary number and mobility ratio. Whereas, the minimal deformation occurs in a stiff medium. The developed hydromechanically coupled pore network model allows parametric study with various conditions, facilitates dimensionless analysis. The dimensionless analysis involves the dimensionless parameters of the capillary number, mobility ratio, particle-level force ratios, and particle-level pressure ratios. This study defines the capillary pressure ratio, defined as the ratio of capillary pressure to fracture pressure and the viscous drag pressure ratio, as the ratio of viscous drag pressure to fracture pressure, and their dimensionless map delineates three deformation regimes — the capillary-induced deformation, drag-driven deformation, and mix-mode deformation. The result reveals that the combination of the capillary pressure ratio at $10^{-1}$ and the viscous drag pressure ratio at $10^{-2}$ define a clear boundary for deformation occurrence. Meanwhile, the effect of fines clogging on the flow pattern and the medium deformation is also investigated using the developed hydromechanically coupled pore network model. The result demonstrates that the fine clogging causes significant alteration in the immiscible fluid invasion pattern and at the same time it induces mechanical deformation associated with conduit opening, attributable to the elevated injection pressure. Surprisingly, weak clogging leads to a significant increase in sweep efficiency when gas invades in water-saturated media

but, severe clogging results in a highly preferential and local flow along a fracture generated. By contrast, clogging during oil invasion in water-saturated media causes a mechanical deformation but with a consistent stable displacement pattern by invading fluid. The presented findings in this dissertation advance our understanding of hydromechanical behavior of deformable porous granular media associated with fluid flows and mechanical deformation at a pore scale, and provide important insights into the effect of fluid-driven deformation on the fluid sweep efficiency, fluid conductivity, mechanical stability of granular media in various engineering practices.