Stokes-Brinkman Flow Simulation Based on 3-D μ-CT Images of Porous Rock Using Grayscale Pore Voxel Permeability

The direct flow simulation using high-resolution micro-computed tomographic (μ-CT) images of porous rock can be used to help understand the flow characteristics at the pore-scale and to estimate fluid properties; however, segmentation of pore space in grayscale 3-D μ-CT images, a necessary step in this process, is challenging because of issues related to the image resolution and pore-filling matrix in the gray-level images. We present a novel process for determining the voxel porosity and permeability of the gray-level regime and evaluating the bulk permeability using the Brinkman force lattice Boltzmann method. In this study, μ-CT images of Berea sandstone are acquired with two spatial resolutions. After the pore size distribution curve is experimentally obtained, the “apparent pore” voxels and “gray pore” voxels are determined based on the designated gray-level values in the gray-level (CT number) histogram, the cumulative and fractional pore volumes, and the linear relationship between CT number and individual voxel porosity. The results show that the boundary between apparent and gray pores in terms of size determines the volumetric fraction and specific surface area. Additionally, the permeability computed by considering the gray pore regime based on the proposed method is more similar to the experimentally measured value than the results of other segmentation methods because the gray pore domain is fully incorporated into the flow domain while preserving the pore connectivity. The proposed sequence of pore segmentation presents a method for handling gray-level pore space without compromising pore connectivity.