Estimation of Conductivity for Nanoporous Materials

摘要

Methods and systems for estimating conductivity of clay mineral systems, and for applying the estimates in larger-scale analysis. Conductivity of the clay may be estimated by constructing a molecular model of an anhydrous charge-neutral clay, and then assigning a charge density by substitution of ions in the model of the clay structure. Counterions are inserted for charge neutrality, and water molecules are added to the model to reflect a selected level of hydration. Following assignment of force-field coefficients, molecular dynamics simulation provides data from which diffusion coefficients can be estimated. Application of the Nernst-Einstein relationship to the diffusion coefficients of the counterions provides the ion conductivity of the clay system. This conductivity can be used to derive a formation factor, and can be applied in direct numerical simulation analysis.

主权项

1. A method of operating a computer system to calculate electrical conductivity in a clay mineral, comprising the steps of:
constructing a molecular representation of a clay mineral, comprised of:
an anhydrous structure of atoms arranged in a plurality of parallel layers, the anhydrous structure including substitution sites in place of metal atoms in the structure at a concentration corresponding to a selected charge density;counterions of at least one species disposed in an interlayer space between layers of the anhydrous structure, at a concentration corresponding to the selected charge density; anda plurality of water molecules disposed in the interlayer space; assigning force field parameters to the molecular representation in combination with boundary conditions corresponding to a selected pressure and temperature condition of the clay mineral; then operating the computer system to perform a molecular dynamics simulation of equations of motion over a simulation time interval, to determine positional coordinates of counterions in the representation at a plurality of times during the simulation time interval; from the positional coordinates at the plurality of times, calculating self-diffusion coefficients for one or more of the species of counterions; and then calculating ion conductivities for a species of counterions from the self-diffusion coefficients.