Upscaling Lithology and Porosity Types from the Microscope to the Core with Thin Section Petrography, Dual Energy CT, and Rock Types: Creation of Diagenesis and Porosity Type Logs
Authors: Jacob M. Proctor, André W. Droxler, Naum Derzhi, Heath H. Hopson, Paul (Mitch) Harris, Pankaj Khanna, and Daniel J. Lehrmann

ABSTRACT The primary objective of this study was to develop and validate a new approach to upscale lithology, diagenesis, and porosity from thin sections to cores using dual energy and multi-scale CT. A new rock typing approach (Genetic Rock Typing) is proposed to upscale diagenetic minerals and pore types, from thin sections to the core domain, to create a diagenesis log. A newly acquired large collection of Late Cambrian short cores from Mason County (Texas) was used for the development and validation of this new rock typing approach. Among the outcropping microbial buildups and their inter buildup sediments, the three main depositional facies, which underwent a wide range of diagenetic alteration pathways, was an adequate sample set to develop and test this new approach. Fractions of diagenetic calcite and diagenetic porosity were upscaled to the core scale using Genetic Rock Types (GRT). From this, we derived a Diagenesis Log at 0.5mm resolution that factors in depositional facies and the diagenetic overprint. The diagenesis log was subdivided based on the number of pore throat size classes within each GRT which provided a framework to distribute porosity types from thin sections to log form. When the predicted extent of diagenetic alteration from the diagenesis log is compared to that quantified for each thin section, a high correlation coefficient is observed (R2 = 0.918).
While this study was restricted to the core domain, whole core dual energy computed tomography (CT) (0.5 mm resolution) mineralogy and total porosity logs were integrated into a multi-scale CT scanning framework. This links directly to the photo electric effect (PE) and bulk density wireline logs because both are x-ray generating instruments and are governed by the same physical laws governing x-ray attenuation. This approach thus has the ability to span 6 orders of magnitude (500 mm to 0.0005 mm). The diagenesis log can be used to extrapolate porosity types from thin sections to logs, from which will generally transform qualitative geologic interpretations into quantitative numbers that petrophysicists, petroleum engineers, reservoir engineers, and geologists can use and rely upon.