A Sensitivity Study of the Effect of Image Resolution on Predicted Petrophysical Properties

Abstract

Micro-CT scanning is a nondestructive technique that can provide three-dimensional images of rock pore structure at a resolution of a few microns. We compute petrophysical properties on three-dimensional images of benchmark rocks: two sandstones (Berea and Doddington) and two limestones (Estaillades and Ketton). We take scans at a voxel size of approximately 2.7 $\upmu \hbox {m}$ and with $1024^3$ voxels for both sandstone and limestone rocks. We numerically upscale the images to image sizes of $512^3, 256^3$ and $128^3$, representing voxel sizes of around 5.4, 10.8, and 21.6 $\upmu \hbox {m}$ respectively, covering the same domains with coarser resolution. We calculate porosity and permeability on these images by using direct simulation and by extracting geometrical equivalent networks. We find that the predicted porosity is fairly insensitive to resolution for sandstones studied with the selected range of resolutions but sensitive for limestones with lower porosity for larger voxel sizes. For the permeability predictions, we do not observe a clear trend in permeability as a function of voxel size; however, sandstones, roughly, have comparable permeability regardless of the voxel size. On the other hand, for limestones, we generally see a decreasing trend in permeability as a function of upscaled voxel size.