Authored by Somayeh Hosseininejad, former PhD candidate in the Department of Geoscience at the University of Calgary and 2014 ASD Students in Mining & Energy TerraSpec Instrument Program selected participant, provides a comparative look at Near-infrared (NIR), X-ray fluorescence (XRF) and scanning electron microscope (SEM) techniques in the mineralogical characterization of mudrock sedimentary system.

This research focuses on the mineralogical characterization of the mudrock formations deposited during Upper Cretaceous time within the interior paleo-sea in Canada (Townships 47-50 and ranges 5-11 west of the second meridian). Multiple cored boreholes were recently drilled by Questerre Energy Corp. in this area, which were used for this study. These units are rich in organic material and are potential oil and gas reservoirs. This study will help in characterizing the reservoir type and quality.

Different techniques were used to acquire mineralogical composition of these rocks. Core samples were analyzed using Energy dispersive X-ray fluorescence (EDXRF) technique, to acquire elemental concentrations of the studied mudrocks. Sampling was done depending on the scale of micro and macro facies variability to characterize the degree of heterogeneity of the strata. Mineralogy was also investigated through other techniques such as XRD and SEM/EDX. Detail petrography work was another helpful step to understand the mineralogy.

With integrating the mineralogy responses that we received using different techniques, we had almost the complete answer for mineralogical and chemical composition of these sedimentary units. Then we decided to take a step further and try the ASD TerraSpec® 4 Hi-Res mineral spectrometer as a complementary technique. NIR spectrometry provides qualitative data and is not able to detect specific mineral compositions such as quartz, however it a reliable technique in identifying clay minerals. It also provides fast and inexpensive data and does not require sample pre-treatment. This allows for higher resolution sampling with minimal analysis time.

The result of this study shows that there is a good correlation between NIR method and XRF in clay mineralogy, although the degree of correlation is related to the quality of the software which we use to interpret the data, as NIR is only able to predict the minerals present in the software library. Also, using the NIR spectrometer in the lab environment is usually associated with higher levels of noise and interference and the fact that the NIR spectra are strongly affected by the physical parameters such as particle size, density and moisture content is the main reason that it is not widely used for laboratory works and specifically fine-grained mudrock systems.

For more information on Somayeh’s research, read the full report Use of NIR Spectroscopy in Mineral Identification in Shale.