Upscaling of Digital Rock Porosities by Correlation with Whole-Core CT Scan Histograms
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SPWLA Distinguished Speaker Series. Digital Rock technologies were developed to augment traditional core analysis and led to a much improved understanding of the microstructure of many rock core types. However, to produce an upscaled description of the reservoir, one must consolidate the measurements in scale over six orders of magnitude. Here, we show that a whole core CT scan may serve as the natural link between the length scales of Digital Rocks and modern logging tools. While the CT scan contains a fingerprint of the structure of the reservoir, the Digital Rock models show the microscopic composition of each CT scan voxel. For upscaling purposes, we established a quadratic correlation between the grey values in a CT scan and the porosities measured on core plugs. This correlation allowed us to generate a synthetic porosity log of millimeter resolution. After that, the length scale was increased by moving averages in the vertical direction. We investigated a thin bed reservoir with layers of halite filled sandstone alternating with layers free of halite at variable layer thicknesses. In this reservoir, the resulting synthetic porosity log compared well with the NMR log porosity within the uncertainty band over a total depth interval of 53.6 meters. We propose that field decisions could be accelerated if the quadratic correlation parameters are general for these types of sediment. In this case, one may generate synthetic porosity logs as soon as the CT scan is available, which is typically the first step in standard core analysis.
Stefan Hertel is a research physicist at Shell Intl. E&P Inc. in Houston, Texas. He holds a master’s degree in physics from the University of Leipzig, Germany and a Ph.D. in physics from the Victoria University of Wellington, New Zealand. In 2018 he was awarded the Giulio Cesare Borgia prize at the International Conference on Magnetic Resonance in Porous Media.