The approach to handle the unresolved pores at 3D X-ray Micro Computed Tomography (μCT) images ofcore samples is developed. It enables a sufficient widening of digital rock studies for tight rocks. The μCTimages of a low-permeable sandstone with a resolution of 1.2 μm/voxel have been generated. Pore SizeDistribution shows the presence of a significant amount of sub-resolution pores. Downsampling has beenapplied to estimate the actual porosity with extrapolation. Visual noise, artifacts, and roundoff errors are the major factors affecting the quality of μCT images. Weapply transform and spatial domain filtering to minimize all the artifacts. Regarding the overall concept ofporosity and through running a geometrical histogram analysis, the Random Walker segmentation as a robustmathematical algorithm has been applied to turn the greyscale μCT images into binary ones resemblingpores and grains. Next, the porosity of the binary images with a resolution of 1.2 μm/voxel has beencalculated. The procedure continues with downsampling to artificially reduce the resolution and calculatethe corresponding porosity.
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