Fourier Transform Infrared Spectroscopy (FTIR) is a technique to determine qualitative and quantitative features of IR-active molecules in organic or inorganic solid, liquid or gas samples. It is a rapid relatively inexpensive method for the analysis of solids that are crystalline, microcrystalline, amorphous, or films. New advances make sample preparation straightforward. FTIR spectroscopy is used by geochemists to determine mineral structure (1), to quantify volatile element concentrations, structural changes in natural minerals and to calibrate data from remote sensing (2). To obtain the best possible IR spectra of samples it is necessary to choose the appropriate IR source, detection method and accessories. For this study I have used attenuated total reflection (ATR) which involves transmitting the IR beam through a crystal that has a moderately high refractive index which results in near-total internal reflection. The instrument used was the Bruker Alpha with a diamond press ATR. This allowed the analysis of small quantities of ground powder with a typical mass of less than 0.5g. The procedure results in absorbance spectra that are reproducible to within +/−5% standard deviation. A set of mineral standards was produced from pure mineral powders of calcite, dolomite, quartz, siderite, apatite, plagioclase feldspar, k-feldspar, kaolinite, chlorite, illite and smectite. Further to this standards were produced from a hydrocarbon powder which allowed quantitative analysis to be undertaken of both organic and inorganic components simultaneously. The sample spectra were evaluated using specific peak picking which produced an average absolute difference between the known and derived mineral concentrations of +/− 3% wt%. The technique does not require a size separation step to assess the weight percent of clay minerals. This therefore means that it has been possible to apply this technology for accurate and comprehensive determination of the major rock forming minerals and organic components at wellsite. Further this the mineralogical and organic components can be used to provide a calculated lithology, acid insoluble component and brittleness index all available at low cost and with a speed that allows key wellsite decisions to be made.
AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015