Fourier Transform Infrared Spectroscopic Determination of Shale Minerals in Reservoir Rocks

Abstract

Attenuated Total Reflectance Fourier transform infrared spectroscopy together with multivariate statistical regression was used to produce calibrations between spectra of standard mineral mixtures and gas shale reservoir rocks. A Classical Least Square (CLS) model was developed from the attenuated spectra of mixtures of five mineral standards chosen to represent the most frequently encountered minerals in shale-type reservoir rocks namely: quartz, illite/smectite (30:70), kaolinite, calcite and dolomite. The CLS model developed was able to quantify the mineral components of independent mixtures with an absolute error between 1 to 3wt% for all the pure minerals in the mixtures. Samples from a suite of shale reservoir rocks were analysed using standard Quantitative X-Ray Diffraction (QXRD) and with FTIR. Unknown mineral concentrations in the samples were then predicted using spectra and the calibration equations. Good correlations were
achieved between the QXRD and ATR-CLS predicted concentrations (r2>0.8), with average absolute error of between 1 to 6wt%. This provides evidence that attenuated FTIR is a promising method for rapid and accurate determination of minerals in reservoir rocks for building higher resolution data
without additional time consuming and expensive traditional analyses.

Keywords: Attenuated Total Reflectance Infrared Fourier Transform Spectroscopy; Classical Least Square analysis; Mineralogy; Reservoir rocks; Shales