Pore-scale simulations of the migration of mobile non-swelling clays in porous media.

Abstract:

The migration of clay fines in geological porous media is a phenomenon of importance in applications such as oil recovery and geological CO₂ storage. When a low-salinity fluid is injected, the clay particles can detach from the grains and clog the pores, leading to a sharp decline in permeability. This process causes a reduction in well injectivity. Clay particles attached to the grains experience three main forces namely, the London-van der Waals attraction, the electric double-layer repulsion, and the Born repulsion forces. The injection of low-salinity fluid results in a hydrodynamic drag on the particles and an expansion of the electric double-layer around the particles, causing them to detach from the grain. In our current work we use computational fluid dynamics to gain insights into the detachment, migration and entrapment of non-swelling clay particles at the pore-scale. We developed a finite-volume based numerical model that uses an immersed boundary method to model the grains and the mobile clay particles as rigid solids. The computational domain is composed of solid and liquid regions. The incompressible Navier-Stokes equations are solved with an added forcing term to ensure rigid-body motion within the solid regions. The numerical method is validated by using existing studies on the drag coefficient on a cylinder at various Reynolds numbers. The collisions between any two solids are modeled using a spring-damper model. The preliminary model results presented will demonstrate the effect of the mean clay particle size and the liquid salinity on the permeability decline for a porous medium with fixed values of porosity and clay concentration. The pore-scale model will eventually provide an improved understanding of the relative importance of the various phenomena and forces at play in the permeability decline process.