Abstract

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) has recently been introduced and is currently being evaluated as a rapid, robust, and efficient technique for simultaneously quantifying kerogen and mineralogy from core and cuttings samples in the laboratory or at the wellsite. The technique we have developed is based on DRIFTS and quantifies mineralogy and kerogen content by measuring the vibrational frequency of chemical bonds. These bonds produce characteristic infrared signatures in common sedimentary minerals as well as organic matter. Core and cuttings samples from wells in unconventional reservoirs in North and South America were analyzed using our standard processing technique and the new full clay processing that solves for kerogen, illite, smectite, kaolinite, and chlorite, in addition to non-clay mineral components. Samples were also analyzed for mineralogy by the more accurate transmission dual range Fourier-transform infrared spectroscopy technique and for total organic carbon (TOC) by LECO/coulometry, and results for both mineralogy and TOC compare very well. The DRIFTS hydrocarbon signal is due to the C-H bond vibrational modes of aliphatic hydrocarbons. For samples of a given maturity, the strength of this absorbance is simply proportional to the hydrocarbon concentration. This signal decreases in magnitude faster than the TOC decreases for samples of differing maturities. As a result, the ratio of TOC to the DRIFTS signal is a new estimate of organic maturity that is shown to agree well with estimates from vitrinite reflectance or Tmax. This ratio is especially sensitive to kerogens that have entered the gas zone. Full DRIFTS analysis including sample preparation generally takes less than 30 minutes for any mud type allowing the technique to keep up with the drill bit at the wellsite.

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