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Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) Analysis of Marcellus Shale with Clay Typing


Horizontal drilling and hydraulic fracturing techniques have made tight shale reservoirs, such as the Marcellus Shale, a more economic source of natural gas. However, due to the cost and the limitations of operating wireline tools in horizontal wells, they are rarely logged. As a result, these important tight shale reservoirs are often poorly characterized. Accurate reservoir characterization is critical to understanding factors that may influence fracturing, completion, and the hydrocarbon production potential of a well. In the absence of log data, a practical and economic solution is necessary to help fill that data gap. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is a method of measuring the vibrations of characteristic chemical bonds in minerals and kerogen for earth materials. A technique has been developed that uses DRIFTS spectra to provide quantitative mineralogy for smectite, illite, kaolinite, chlorite, muscovite, quartz, calcite, and dolomite with an accuracy of ±5 wt%. The technique also simultaneously estimates kerogen or organic matter concentrations and calculates estimated total organic carbon (TOC). In addition, the DRIFTS technique provides information that can be used to estimate kerogen maturity. Understanding the mineralogy of a formation, especially the clay mineralogy, can affect completion quality and production of a well. For this study, 223 samples were collected by a mud logging company from a well in the Marcellus formation. DRIFTS mineralogy results were validated on a subset of samples by four independent data sources including transmission dual-range Fourier transform infrared spectroscopy, X-ray fluorescence, TOC by coulometry, and RockEval pyrolysis. Mineralogy and kerogen concentrations are presented to demonstrate the value added by the DRIFTS technique to the characterization of horizontal wells while drilling.