Characterization of petrophysical properties using pore-network and lattice-Boltzmann modelling: Choice of method and image sub-volume size
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2016 Elsevier B.V. The invention and progression of micro-CT scanning technology has significantly improved the quality and resolution of tomographic images. It is now possible to fully resolve simpler pore systems and thus perform static modelling of flow properties. A substantial amount of research has been performed to fully develop workflows relating to the analysis of a number of sandstone and carbonate core samples from benchmark outcrop rocks. In this study the focus is on Bentheimer, Clashach and Doddington sandstone rocks and on Estaillades, Ketton and Portland limestone samples. These benchmarks have been imaged using a micro-CT at a resolution of about 3 m. The image-based modelling and analysis of the absolute permeabilities gave values within a similar range of the experimental results for all three of the sandstone samples. Results deviated greatly for the limestone due to the presence of unresolvable pore space, reflecting the need to acquire higher resolution data to obtain a full digital description of the samples at hand. The variation in the petrophysical parameters with the size of the selected subvolume (either 512 or 1024 voxels) is the focus in the present study. With the notable exception of Clashach, the homogeneous sandstones do give the same results for the two subset sizes. The limestone data varies by more than a factor of four for the permeabilities whereas the porosity varies by less than a factor of two. The extracted pore size distributions vary quite significantly from the experimental ones regardless of the subset size and the bimodal nature of the limestone pore space is not captured at all. This is reflected in the capillary pressure curves, the image-based ones are significantly different from the experimental ones. The reconstructed 3D acquisitions and 2D slices will be posted online to form a database that allows for download of the tomographic images and extracted pore spaces to serve as a resource for future comparative modelling studies.
