Towards inferring elastic moduli for argillaceous sandstones: clay content estimation in drill core utilizing hyperspectral imaging [Master thesis]

This study investigates the feasibility of using hyperspectral imaging to estimate relative clay content in siliciclastic drill core as volumetric clay fraction provides a piece of the puzzle to infer elastic moduli in argillaceous sandstones, a task relevant to geomechanical modeling for CCS purposes. Towards this end, a new laboratory system for drill core scanning was set up and used to acquire VNIR-SWIR hyperspectral images of drill core sections. Images were acquired from 54 boxes of drill core of the Gassum Formation, an important reservoir candidate for Danish CCS projects. Spectral unmixing analysis and minimum wavelength mapping were used to attempt to estimate clay percentages throughout six of the drill core specimens that were scanned. Both approaches confirmed the presence of clay in the imaged specimens, but several challenges arose to derive the actual clay fractions needed to infer elastic moduli, in particular the need to ground-truth the clay contents with those inferred here from the imaging analysis. First-order clay percentage estimates are provided for three of the drill core specimens analyzed, but the other three did not yield robust results. It is suggested that these latter specimens are too homogenous for the unmixing approaches utilized in this study. The results motivate further work on clay content estimation by hyperspectral analysis to potentially provide a non-destructive workflow to obtain elastic moduli by proxy.