DEVELOPMENT OF NEW SHALE GEOCHEMICAL REFERENCE MATERIALS: RESULTS FROM BOQUILLAS SHALE INTERLABORATORY TESTING AND OTHER STATUS UPDATES

Geochemical reference materials (GRM) relevant to source rocks from unconventional petroleum systems in the continental United States are being developed by the U.S. Geological Survey. A GRM under development using shale from the Late Cretaceous Boquillas Formation (ShBOQ-1) collected from a roadcut in southern Texas (ShBOQ-1) has undergone extensive interlaboratory testing to determine (1) major and trace element concentrations, (2) total organic carbon (TOC) content and programmed pyrolysis parameters, and (3) X-ray diffraction (XRD) mineralogy. The International Association of Geoanalysts recently used the ShBOQ-1 in their proficiency testing program (GeoPT40A), and determined concentrations for 56 elements or other analytes by 99 laboratories. The results of this study demonstrate the homogeneity of the GRM and indicate that it is viable for organic geochemical and mineralogical standardization. Results from participating industry, academic, and government geochemistry laboratories (12) show consistent mineralogical results for major phases on an organic-free basis (average wt. % with standard deviations): calcite 63 ± 3, quartz 23 ± 3, kaolinite 8 ± 2, and pyrite 1.5 ± 1. We have also quantified variability in TOC and programmed pyrolysis parameters based on data from a variety of different instrument types (average values with standard deviations): TOC 5.07 ± 0.16 wt. %; S2 hydrocarbon-generating potential 32.2 ± 2.9 mg/g; and Tmax 424.0 ± 1.4 °C. Additional petrographic studies are underway and similar characterization work is planned for four other GRMs that have been collected from the Late Cretaceous Mancos Shale (Piceance Basin), Devonian–Mississippian Woodford Shale (Anadarko Basin), Late Cretaceous Niobrara Shale (Denver-Julesburg Basin), and Middle Devonian Marcellus Shale (Appalachian Basin). These new GRMs will provide the petroleum industry and geochemistry community with matrix-matched materials facilitating best analytical practices and data quality assurance and control.