--> Longwave Infrared (8-12 μm) Spectral Imaging for the Automated Mapping of Lithofacies in Athabasca Oil Sands Core

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Longwave Infrared (8-12 μm) Spectral Imaging for the Automated Mapping of Lithofacies in Athabasca Oil Sands Core

Abstract

Core logging is the principal method for investigating the subsurface in oil sands industry operations and every drilling season immense time and funds are dedicated to this labour-intensive process. In this study, we provide a first investigation of longwave infrared (LWIR, 8-12 μm) spectral imaging for the automated mapping of lithofacies in oil sands drill core. A dry core from the Kearl Lake area of the Athabasca deposit was used, spanning from Devonian carbonates at the base to upper McMurray Fm. at the top. The first step of the investigation was to build a spectral library for six lithofacies represented in the core: oil sand, clean sand, siltstone, mudstone, siderite and Devonian carbonates. Type sections of each were identified by visual inspection of the core. High resolution (293 bands) reflectance spectra were collected from 2 mm spots on the core using a hand-held FTIR (Fourier transform infrared) spectrometer. Individual spot spectra are the average of 64 scans and library spectra were produced by averaging 3 or more spot measurements for each lithofacies. FTIR spectra revealed unique spectral signatures in the 8-12 μm region for each lithofacies. For example, oil sand, clean siltstone and mudstone showed a systematic change in the shape of the 9 μm reflectance peak, which can be attributed to a decreasing quartz to clay ratio. FTIR spectra were compared to lower resolution spectra (35 bands) collected from LWIR spectral imagery of the core. A LWIR spectrum was collected for each lithofacies by averaging pixels from the same spots on the core used for FTIR measurements (∼80 pixels/1 cm spot). FTIR spectra were resampled to the resolution and range of the LWIR spectra, allowing direct comparison of the two data sets. Resampled FTIR results closely matched that of the LWIR spectra from the imagery; unique spectral characteristics, such as the change in shape of the 9 μm peak, could be observed even at low resolution. Using the image-derived spectra, an automatic classification technique was applied to the LWIR imagery to map the occurrence of each lithofacies in various boxes of core from the sample suite. The resulting core maps agree with visual inspection of the core and all six lithofacies were successfully classified. With a spectral library provided, the creation of spectral lithofacies maps is a fast and simple process, which suggests that this technique may have the potential to increase the efficiency of core logging in the oil sands.