Lattice Boltzmann prediction of transport properties in reconstructed nanostructures of organic matters in shales

TL;DR

This study uses lattice Boltzmann simulations on reconstructed nanostructures of shale organic matter to predict transport properties, revealing the influence of pore size and overlap on diffusivity and permeability, and proposing modified equations for better accuracy.

Contribution

It introduces a pore-scale model based on the lattice Boltzmann method for predicting transport properties in reconstructed shale organic matter structures, with new correction equations for permeability and diffusivity.

Findings

Mean pore diameter and overlap tolerance significantly affect transport properties.

Modified Bruggeman equation provides better diffusivity estimates.

Knudsen corrections align closely with numerical results.

Abstract

Size, morphology and distributions of pores in organic matters of shale matrix are discussed based on high resolution images from experiments in the literature. 150 nanoscale structures of the organic matters are then reconstructed by randomly placing pore spheres with different diameters and overlap tolerances. Effects of porosity, the mean diameter and the overlap tolerance on void space connectivity and pore size distribution are studied. Further, a pore-scale model based on the Lattice Boltzmann method is developed to predict the Knudsen diffusivity and permeability of the reconstructed organic matters. The simulation results show that the mean pore diameter and overlap tolerance significantly affect the transport properties. The predicted Knudsen effective diffusivity is compared with Bruggeman equation and it is found that this equation underestimate the tortuosity. A modified Bruggeman equation is proposed based on the simulation results. The predicted intrinsic permeability is in acceptable agreement with Kozeny-Carman (KC) equation. In addition, a relationship is developed to determine the apparent permeability based on Knudsen diffusivity and intrinsic permeability. The predicted apparent permeability is compared with that predicted by various corrections in the literature. Knudsen's corrections match best with our numerical results and are recommended to calculate the apparent permeability.