Hyperspectral Imaging and Geochemical Characterization of an Eagle Ford Shale Core

Abstract

The similarity in appearance of dark-colored mudrocks can mislead even skilled examiners to describe such units as homogeneous, where further detailed geochemical analysis often reveals substantial variation in organic matter content and mineralogy. Capturing the variability in mudrock composition in a particular stratigraphic interval requires extensive analytical work performed on many samples. Hyperspectral imaging provides high-resolution characterization of mudrock core that can augment information from geochemical measurements of bulk samples and geophysical well logging data for interpretation of lithology and variability in resource potential. Recently, several mudrock cores from the U.S. Geological Survey Core Research Center were scanned using an integrated imaging system that generates high-resolution photographs (50 mm), 3D laser profiles (20 mm), and hyperspectral data (500 mm resolution, 450 – 2500 nm range). A core through Upper Cretaceous strata collected in Waco, Texas containing portions of the Del Rio Formation, Pepper Shale, lower and upper Eagle Ford Shale, and Austin Chalk is the focus of this study (~600 ft total). The hyperspectral results were compared to measurements of geochemical and mineralogical properties conducted on grab samples from approximately every two feet along with a typical suite of well logs. Mineral class maps and individual spatial distribution purity maps of particular minerals generated using the hyperspectral imaging data clearly delineate chemofacies boundaries that are consistent with the geochemical and mineralogical characterization, but are not immediately discernable from direct examination of the core or from high-resolution photographs. The fine grain size and high organic content in the lower Eagle Ford does reduce detection of some mineral species (including carbonates), but a distinctive aspectral signature distinguished the lower Eagle Ford from the more clay-rich and organic-lean units. Hydrocarbon spectral features reflect the high concentration of hydrogen-rich kerogen in the lower chemofacies of the lower Eagle Ford. Significant variability in clay content is a key feature of the different lithologies in the core and is attributed to fluctuating sea level and other variability in the depositional environment. Overall, the hyperspectral imaging results are confirmed by other datasets collected on the core and provide great detail on the variability in mudrock composition in the Eagle Ford.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018