Pore-scale prediction of transport properties in reconstructed nanostructures of organic matter in shales

Abstract

h i g h l i g h t sPore morphology in organic matter is discussed. 250 nanoscale structures of the organic matter are reconstructed. Pore connectivity and pore size distributions of organic matter pores are analyzed. Pore-scale modeling is conducted to predict permeability and diffusivity. Apparent permeability is predicted and compared with empirical correlations. a b s t r a c tSize, morphology and distributions of pores in organic matter of shale matrix are discussed based on high resolution images from experiments in the literature. 250 nanoscale structures of the organic matter 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. Furthermore, a pore-scale model based on the lattice Boltzmann method developed in a previous study is used to predict the Knudsen diffusivity and permeability of the reconstructed organic matter. 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 underestimates 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, the apparent permeability is determined based on Knudsen diffusivity and intrinsic permeability predicted. The apparent permeability is compared with that obtained with various correlations in the literature. Knudsen's correlations match best with our numerical results and are recommended for calculating the apparent permeability.

Apparent permeability prediction of organic shale with generalized lattice Boltzmann model considering surface diffusion effect

“…However, because of the complexity of boundary conditions, most of the applications of the slip-based LBM are limited to single channel or bundle of channels [23]. Recently, Chen et al [20,24] proposed a LB model based on the Dusty gas model (DGM) to predict the apparent permeability of shales with complex porous structures, where the complexity of the slip boundary conditions are avoided. Very recently, Chen et al [25] improved the generalized lattice Boltzmann model (GLBM) proposed by Guo and Zhao [26] for fluid flow through porous media by including the Klinkenberg effect, and performed several simulations based on heterogeneous shale matrix with natural fractures, organic matter and inorganic minerals [25,27].…”

Permeability prediction of shale matrix reconstructed using the elementary building block model

“…534 Therefore, the results indicate that InterP pores can effectively [1,2,4,5,7,9], in which fluid flow is characterized as rela-545 tively high Kn flow due to the small pore size [10,32]. In our previ-546 ous studies [11,12], porous structures of shales were reconstructed node is calculated using Eq. (5) [33], then Kn is calculated using the 556 mean free path and the pore size, and finally Eq.…”

“…Due to such a structural 77 heterogeneity, it is expected that fluid flow in shale matrix is very http complex. Complicating matters more is the gas slippage because 79 typical pore size in shale matrix is from a few nanometers to a 80 few microns [6,9], leading to gas transport with relatively high 81 Knudsen number (Kn, ratio between the mean free path of gas 82 molecules and the characteristic pore size of a porous medium) 83 [10][11][12]. Further, adsorbed gas in shale matrix particularly in OM 84 with higher affinity also plays a role on the gas transport in shale 85 matrix [13][14][15][16].…”

Study of the numerical simulation of tight sandstone gas molecular diffusion based on digital core technology

“…However, in existing studies, models are just simplified ideal models which do not represent the real pore structure of tight gas reservoirs. In this study, a refined digital model of the pore structure of tight sandstone reservoirs was built using advanced digital core technology (Guo et al 2016;Chen et al 2015;Liu et al 2014Liu et al , 2017Ni et al 2017;Yin et al 2016), and a numerical simulation of molecular diffusion was conducted on the basis of the model. This has provided new ideas for the study of the micro-mechanisms of molecular diffusion of tight gas.…”