--> Mineralogical and Petrophysical Characterisation of a Fine Grained Sandstone With Significant Clay Coating Using 3-D Micro-CT and SEM Imaging From a 5mm Plug

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Mineralogical and Petrophysical Characterisation of a Fine Grained Sandstone With Significant Clay Coating Using 3-D Micro-CT and SEM Imaging From a 5mm Plug

Abstract

This project demonstrates how high resolution 3D X-ray microcomputed tomographic (micro-CT) imaging integrated with higher resolution SEM imaging and automated quantitative mineral mapping may be used to digitally determine petrophysical properties (e.g. porosity, permeability, relative permeability, capillary pressure curves, formation resistivity factor, Archie's cementation exponent, grain size distribution, pore and throat size distribution, water saturation, and elastic properties. The workflow was established on a sub-plug (5mm long by 5mm diameter) from a core plug of an Australian Jurassic, fine grained sandstone with significant grain coating. High resolution 3D micro-CT images of the sub-plug were acquired in as-received state and after saturating it with X-ray dense brine. The images were registered in 3D into perfect geometric alignment then a difference map was created of the connected porosity including pores that are below the resolution of the micro-CT images. The sample contains a lot of pore-filling materials and the grains are coated by clay. Segmentation of the 3D tomograms was carried out to map the 3D distribution of the grain coatings and other minerals and capture resolved as well as sub-resolution porosity. BSEM imaging (at higher resolution than the micro-CT images) of a polished section through the sub-plug was performed to better characterise the porosity of the pore-filling and grain-coating minerals and automated quantified mineral mapping by SEM-EDS (QEMSCAN™) was performed to identify the minerals and improve the segmentation. A pore network was then extracted from the segmented images and used as input into a quasi-static pore network model for multiphase simulations. The capillary pressure simulation was compared with experimental mercury injection data. There is a good agreement between the simulated and experimental data in the resolved porosity (macroporous) region of the curve.