Petrophysical characterization of tight oil sandstones by microscale X-ray computed tomography

Abstract

Tight oil sandstones have complex pore structure due to multiple pore types and multiscale pore size ranging from several nanometers to dozens of microns. In this study, petrophyiscal properties of tight oil sandstones were quantified based on microscale X-ray computed tomography (μXCT) imaging techniques. The pore types in gray scale images were identified; porosity, pore size distribution (PSD), and pore connectivity were analyzed from segmented image stacks; and their permeability was calculated by representative elementary volume (REV) scale lattice Boltzmann method (LBM). Three types of pores including residual interparticle pores, grain dissolution pores and micro fractures were identified. A multi-threshold segmentation algorithm was applied to segment the image stacks into three constituents, namely, pore, matrix, and clay. The calculated volumetric fraction of the pore constituent from the segmented image stacks was smaller than experimental porosity, because a certain amount of porosity was also contributed by clay constituent. The PSD of the samples was found to be unimodal in the range of 3–69 μm, with the peak at around 10–15 μm. The clay constituent led to the increase in the overall connectivity of the images stacks, indicating that clays bridged the isolated pores. By assigning appropriate porosity and permeability to the clay constituent, calculated permeability of the samples using REV scale LBM well matched the experimental data. This study provides new insight into characterization of pore structure of tight oil sandstones by μXCT technique.