Modeling of Bentonite Hydration Using Nonlinear Diffusion Model

摘要

We deal with a modeling of bentonite behavior during the hydration process. Bentonite is a type of clay with water adsorption and swelling ability. It leads to a complex nonlinear behavior in contact with water and to nontrivial problems for numerical solution. In our work, we deal with a model problem of water transport as a point inflow from the rock fractures which brings asymmetric and nonhomogeneous conditions unlike the existing studies with simpler uniform hydration. The problem is solved using nonlinear diffusion equation. In contrast to other porous materials, the formulation requires deriving special nonlinear diffusivity coefficients for bentonite. We use finite element method within the commercial software ANSYS for the numerical solution. An additional improvement in the problem solution is brought by multi-scale approach: a simpler 2D axisymmetric model with one fracture in larger scale which is used for an estimation of boundary conditions for small-scale 3D models with several variously distributed fractures, in particular a third-type condition with a non-linear relation between the saturation (the primary variable) and flux (a derivative).