Study of Nanoparticle Adsorption and Release in Porous Media Based on the DLVO Theory

Abstract

Abstract Nanoparticles are usually small enough that they can pass through the porous media without mechanically plugging the pore throats. However, physicochemical interaction between the nanoparticles and the pore walls can cause significant retention of nanoparticles. The objective of this paper is to provide theoretical equations based on DLVO theory to calculate the rate of deposition and release at different temperatures, ionic strengths, and pH values. DLVO theory is used to understand the interaction between nanoparticles and rock minerals. Electrostatic interaction depends on the zeta potential of nanoparticles and pore surface. In this paper, an equation is developed to calculate zeta potential at different temperatures, ionic strengths, and pH values. The rate of deposition and release of Silica nanoparticles in a sandstone formation, where interaction energy profile has energy barrier, has been derived. To validate the theoretically calculated rates, a numerical model is developed to compare the theoretical calculations with experimental data. Increasing ionic strength and temperature decreases the energy barrier height and hence increases the rate of deposition. The effect of pH on the rate of deposition depends on the location of environment pH with respect to the isoelectric point of nanoparticles and rock surface. For extreme values of pH, energy barrier exists and rate of deposition is low. However, when the pH of the solution is between the isoelectric points of nanoparticles and rock surface, the energy barrier decreases and the rate of deposition increases. The rate of deposition is time dependent with the rate decreasing as more rock surface is covered by nanoparticles. These theoretically calculated rate values are used in a numerical model of the advection-dispersion equation with source/sink term. Several experimental data have been perfectly matched with the model that validates the theoretical calculations of the rate of deposition. The new mechanistic model for nanoparticles can be used to determine the fate of nanoparticles in porous media under different conditions of nanoparticle size, temperature, ionic strength, and pH. This model can help to understand the nanoparticles transport in porous media and effectively design nanoparticles fluid for injection into oil and gas reservoirs.