AAPG Foundation 2019 Grants-in-Aid Projects

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Applying automated X-Ray Fluorescence (XRF) and Laser Induced Breakdown Spectroscopy (LIBs) to high vertical resolution characterization for chemostratigraphy and petrotyping on Meramec


Unlike conventional reservoirs, it is challenging to develop tight formations, due to their significant vertical and horizontal heterogeneities. Many real-time field decisions, such as lateral placement, are made with the understanding of sequence stratigraphy and well’s petrophysical profile. Handheld X-Ray fluorescence (XRF) has been commonly used as a rapid scanning tool for elemental analysis on geochemical samples. Complimentary to XRF, handheld Laser Induced Breakdown Spectroscopy (LIBS) has recently been developed, but quickly considered as a useful tool. It captures the light elements, which XRF cannot, such as sodium, magnesium and more importantly carbon (both organic and inorganic), which are essential elements to understand rich organic sedimentary rocks. LIBS spectra generally have lower emission signal intensity for organic rich samples. Therefore, it is important to select optimal integration-delay time to capture better signal intensity for all emission lines ranging from the ultraviolet (180-400nm), through visible light (400-780nm) to infrared domains (780-960nm). Using a partial least square regression (PLS) and signal normalization, an inversion method was developed for rock slab samples. The trained dataset includes 150 samples from different tight formations, such as Meramec, Woodford, Eagle Ford, Barnett, Bakken, Vaca Muerta and Wolfcamp. The inversion provides quantitative elemental concentration results with reasonable uncertainty. The results were validated with 70 samples from different shale plays. XRF was obtained for the same samples and results showed a good correlation between LIBS and XRF for major elements (Al, Fe, Si, Mg, Si, Ca, K). Total carbon measured through LECO without acidizing was used to verify LIBS total carbon readings. With major elements abundance, mineralogy was determined; this provided carbonates concentration, which was used to calculate inorganic carbon. Organic carbon (TOC) was later estimated as the difference between total carbon and inorganic carbon. In this study, we demonstrated the complete elemental analysis on 400-ft of core sampled at a 1-foot depth resolution using both XRF and LIBS. The finished scan was achieved within reasonably short field time. Trace elements were used to understand formation chemostratigraphy, while major elements were used to invert for mineralogy and TOC.