USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE A comparative look at NIR, XRF and SEM techniques

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1 USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE A comparative look at NIR, XRF and SEM techniques Somayeh Hosseininejad, Per Kent Pedersen, Ronald James Spencer, Festus Michael Uwuilekhue Department Of Geoscience, University Of Calgary CENTRE FOR APPLIED BASIN STUDIES

2 Alberta Saskatchewan Manitoba Arborfield Carrot River 0 MESOZOIC WILDCAT HILL PROVINCIAL PARK Ashville Upper B elle Fourche r oyne membe Gammon Mb member INTRODUCTION Paleogeography: The Upper Cretaceous sedimentary package of interest was deposited on the eastern margin of the Western Interior Seaway currently located in central-eastern of the Saskatchewan province. a: Paleo-geography map of the study area during late Cenomanian-early to mid Turonian and the position of the Western Interior Seaway (WIS) during that time. b: Paleo-map showing the position of the study area with respect to the position of paleo-shoreline and the current Cretaceous outcrop (manitoba escarpment) (modified from Kauffman, 1969). a. b. Boreal Sea Western Interior Seaway Study Area Hudson Seaway 60 N 45 N 30 N CANADA U.S.A. Western Interior Seaway Sask. 0 Km 500 Early Turonian Shoreline Position (after Kauffman, 1969) 1000km Early Turonian Paleolatitude (Sageman and Arthur,1994) Current Outcrop Edge (after McNeil and Caldwell,1981) Study Area Pasquia Hills Porcupine Hills Manitoba Escarpment Duck Mountain T52 T50 T48 T46 R13 R11 R9 R7 R5 R3W W W W W W W W W W W W W W W2 R13 R11 R9 R7 R5 R3W2 Current Pasquia Hills outcrop Viewed Well location Analyzed Well location T52 T50 T48 T46 Study area and core location: Study area is located in east-central Saskatchewan close to the current Pasquia Hills outcrop as indicated by black rectangle (left) and dashed red line (right). Stratigraphy: a:upper-cretaceous stratigraphic chart and high and low frequency sea-level curve (after MacNail, 2009 and Dean et al. 1998). b: Typical induction and resistivity log response for the studied interval. In this study, the upper part of the Belle-Fourche, Second White Speckled including Keld and members as well as the lower part of Carlile were analyzed. a. Period and Era Cretaceous Late Early Stage Companian Albian Cenomanian Turonian Santonian Conemancian Ma Southwest Manitoba Nicolas, 2009 Carlile 2WS Ashville upper lower Pierre Shale upper lower Boyne Laurier limestone Keld Belle Fourche Base of Fish Scale Zone Westgate Skull Creek Swan River Sea level Changes/OAE s McNeil (2009), Dean et al. (1998) Deeping Shallowing OAE III OAE II OAE I Greenhorn cyclothem Niobrara cyclothem cycles Movry cyclothem 55 O30 b. L-Pierre Shale Favel Carlile B. Keld Mb 350 m 450 m / /00 100/ /00 SP 20 0 R 20 USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE 2

3 Objectives: (i) to estimate mineralogical composition specifically clay mineralogy from the spectra, (ii) to qualitatively compare mineral concentrations calculated from XRF and XRD analyses, as well as mineral groups identified through SEM and microscopic petrography work with NIR results. NIR spectroscopy has been widely used in different scientific fields such as biology and medicine. However, it has been rarely used in mineral identification in finer sedimentary rocks specifically mudrocks. This work will allow us to verify the accuracy of this technique compared with XRF and XRD. The figure below compares NIR with the other methods used regarding price and ease of use. Increasing cost of experiment NIR XRF XRD SEM Qualitative Quantitative Quantitative Qualitative Increasing ease-of-use Chart comparing different techniques for mineral identification in this study including XRF, XRD and SEM along with NIR spectroscopy. Methodology: What is (Near-Infrared) NIR Spectroscopy? Visible Near-Infrared spectroscopy is a relatively new nondestructive method for mineral analysis. The method is based on activating chemical bonds by irradiating mineral mixtures thereby creating resonance vibration. Accordingly, the energy of the spectrum is reduced thereby generating an absorption spectrum whose position in the spectra region indicates the type of bonds and in many cases the minerals associated with them. The non-destructive reflection spectroscopy operates in the visible to Near Infrared region and has been utilized to identify all common clay minerals as well as sulfates, hydroxides and carbonates (Viscarra et. al, 2008). Due to their distinct spectral characteristics, clay minerals are easily identified using this method (Stefano, 2003), in addition to XRD and other mineralogical data, extensive mineral analysis can be done utilizing the method. The spectra produced from vis-nir NIR flowchart Near Infrared light radiation Chemical bond activation Creating resonance vibration Generating an absorbtion spectrum Data interpretation using software with proper mineral library Mineral Identification spectroscopy are commonly interpreted using appropriate computer based software with calibrated digital mineral libraries for fast and easy mineral identification. What is being measured? A standard spectroscope measures direct transmittance as a percentage (%T); this represents the percentage of the incident beam of light transmitted by the sample. This value is then used to calculate absorbance: Abs=log(1/T) T=Transmittance=%T/100 A number of things happen when a beam of light comes into contact with a solid. The beam may be reflected, transmitted, diffused, absorbed, refracted or polarized. The respective likelihood of these outcomes depends on the incident beam s angle of incidence in relation to the solid. With NIR spectroscopy, it becomes possible to measure the different percentages of the light reflected, transmitted or absorbed by the sample, whilst it takes into account the various phenomenon capable of producing misleading measurements such as diffusion, refraction and polarization. The spectral range covered is between 350 to 2500 nm. a. b. Absorption Scatter Incident beam Front reflection Back reflection Transmission Refraction Polarization Cosmic ɣ-rays X-Rays UV V Radio Waves I IR Rays S Micro UHF Short Med Long nm 10 nm nm Visible Infrared Fundamental Far Near Infrared Ultra Violet 10 nm ,500 50,000 nm a: Types of light Interactions with a solid. b: NIR reflectance spectra of mineral samples Equipment and Software Terraspec 4 Hi-Resolution mineral spectrometer with a contact probe attachment (for whole core samples) and mug light sampler (for powdered rock samples) was used in this analysis. Data capture was achieved using Indico Pro spectral acquisition software. The instrument (supplied by Analytical Spectral Devices, Boulder Colorado) has a spectral range between nm. Prior to scanning, the spectrometer was calibrated with a Spectralon white tile, this procedure was repeated every 10 minutes (auto timed for consistency) to ensure accurate mineral spectral capture. To improve signal to noise ratio, the instrument sample count rate was set at 200. The acquired spectral data was then analyzed and interpreted using The Spectral Geologist (TSG) Pro 7.1 software equipped with digital mineral libraries for mineral identification based on their unique spectral signatures. a: Spectrometer device, b: Powder samples used in this study, c: Using spectrometer on core samples. USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE 3

4 Silt VF F M C VC Gravel Quantitative XRF Mineralogy: Main Minerals RESULTS a. well ID: (wt%) (wt%) Toal Clay (wt%) (wt%) (wt%) Cross plots of major and 55 accessory mineral percentages 60 vs. depth for the well W2 using ED-XRF analysis. 65 This analysis was done on powder samples using mortar 70 and pistol to achieve higher 75 accuracy. Also showing the lithology log along with gamma and resistivity log. Straight horizontal lines are indicating 85 the boundaries between 90 different members within the studied interval. Major mineralogical changes occur along these boundaries indicating a change in sediment source as a result of sea-level fluctuation or change in the oceanographic state of the sea. The highest values for resistivity correspond to the highest carbonate content in the rock and highly cemented intervals. The abnormally high gamma values are related to thick to thin fish bone and bentonite beds. The inverse relationship between quartz and carbonate contents indicates different sources. In these sediments quartz is mainly detrital and different forms of carbonate minerals are mainly present as parts of calcareous fossil fragments as well as carbonate cement. are shown in more detail in the next figure. Apatite (wt%) Lithology Log Mud Gamma Resistivity API-GR OHM-M 1 10 Keld L-Colorado Unit Belle Fourche MB. b. Clay Minerals well ID: Total Clay well ID: Total Clay Cross-plots of clay minerals vs. depth for the two wells of W2 and using the XRF technique. Values are in weight percentages. Highest clay contents usually occur at the base of each parasequence, indicating the progradational nature of these units. Keld L-Colorado Unit BF Keld L-Colorado Unit BF Lower ratios of illite and smectite indicate lower depth of burial and lack of maturity in the sediments. In these sediments is usually present as cement in pore spaces. Qualitative SEM Mineralogy: Scanning electron microscopic images showing different groups of minerals including silicates, carbonates, sulfates and phosphates. SEM helps to study different minerals within the fabric of the rock. Silicate minerals include quartz and clay with minor amounts of feldspar. is present both as detrital grains and replacement cement. are mostly autogenic. Carbonates are in different Silicates Carbonates Sulfates forms such as calcite, as the most prominent, dolomite, siderite and ankerite. Minor mineral groups include Phosphates Phosphatic Phosphatic Phosphatic pyrite and phosphates. fish bone Phosphatic Apatite fish bone fish bone Apatite fish bone Phosphate is present in two Dolomite forms of apatite grains and Dolomite Silicfied shell fragment fish fragments. Silicfied shell fragment / / USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE 4

5 Second White Speckled RESULTS AND DISCUSSION Quantitative NIR Mineralogy: Keld Belle Fourche Spectrum plots for individual minerals present within each unit. Each mineral has a specific spectral signature, however, there are some overlaps in the spectral band produced by the minerals which makes the distinction between minerals a more challenging process. Despite the presence of significant amounts of carbonate in the, this mineral has not been detected in this unit for unknown reasons. The most mineral diversity has been detected in the Keld (only major plots are presented here). Comparison: NIR XRF XRD SEM, normal and Fluorescent light Petrography Carlile Carbonate /, Apatite, /Mica /Plagioclase /Plagioclase Keld (Carbonate) (Carbonate),, Zoisite (Epidote) Carbonate, / Pyite, Apatite, /, Apatite, /Mica /Plagioclase /Mica /Plagioclase, Dolomite, /smectite Feldespar/Plagioclase, apatite, phosphate, Dolomite /smectite Feldespar/Plagioclase, apatite, phosphate Belle Fourche Belle-Fourche, pyrite /, Apatite, /Mica /Plagioclase Feldespar/Plagioclase, USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE 5

6 Conclusion: NIR includes the least amount of sample preparation as well as measurement time. This feature makes the NIR one of the best techniques used for quick mineral identification in the field. Use of the NIR instrument in laboratory conditions is usually associated with higher levels of noise. The NIR instrument predicts different minerals present in the sample as a function of their near infrared (NIR) diffuse reflectance spectra. Minerals that do not have detectable response within that wavelength will not be detected. For example NIR is unable to identify quartz content as this mineral does not have a spectral response in the UV-vis-NIR range. NIR spectroscopy is found to be accurate and reliable in clay mineral identification compared with XRF and XRD method. NIR, unlike XRF and XRD, is a qualitative technique and one of the main difficulties to apply the NIR spectroscopy obtained from mudrock in quantitative form is the presence of broad and superimposed bands and the low absorption intensities. The fact that the spectra are strongly impacted by physical parameters (e.g., particle size, density, and moisture content) is the reason that NIR is not widely used in laboratory work specifically with fine grained mudrock samples. Another factor that interfere the NIR spectra from minerals is presence of organic material in the context of rock. Shale and mudrocks are one of the richest rock-types in terms of organic matter content. This fact makes the use of NIR spectroscopy more challenging for mudrock samples. The other challenge associated with the NIR technique is making use of the proper software with an appropriate mineral library (calibration) to interpret the data. In fact, NIR is only able to predict the minerals within the diversity of samples in the library. In order to achieve the best results from NIR spectroscopy, it is crucial to create a library specifically designed for each study. To create a complete designated library one has to use other available techniques such as XRF or XRD prior to using NIR. Table comparing different methods of analysis for mineral identification in this study including XRF, XRF, NIR and SEM. There is a good correlation in clay mineralogy between NIR method and the other techniques. NIR proves poor in major mineral detection such as calcite and quartz. Acknowledgements The authors would like to thank Analytical Spectral Devices, Boulder Colorado, for granting us the spectrometer and providing technical support. This study was supported by funds from Questerre Energy Corporation. References Bowtiz J. and Ehling, A., 2008, Non-destructive Infrared Analyses: a method for provenance analysis of sandstone, Environmental Geology, Vol. 56, Pg Stefano, C. J., Calrson, E. H., Ortiz, J. D., 2003, Clay Mineral Identification by Diffuse Spectral Reflectance, Geological Society of America, Abstracts with Programs, Vol. 35, No. 2, Pg. 18. Viscarra Rossel R.A., Walvoort D.J., McBratney A.B., Janik L.J., Skjemstad J.O., 2006, Visible, Near Infrared, Mid Infrared or Combined Diffuse Reflectance Spectroscopy for Simultaneous Assessment of Various Soil Properties, Geoderma, Vol: 131, Pg Bozkurt, Alper; Rosen, Arye; Rosen, Harel; Onaral, Banu (2005). A portable near infrared spectroscopy system for bedside monitoring of newborn Brain, BioMedical Engineering OnLine* *4* (1): 29. USE OF NIR SPECTROSCOPY IN MINERAL IDENTIFICATION IN SHALE 6