Boquillas Shale Reference Material ShBOQ-1: A USGS Standard for Carbonate Source Rocks

The road cut off US-90 west of Del Rio, Val Verde County, Texas, after the ShBOQ-1 material was collected. USGS / Justin E. Birdwell, 2015.

What a reference material is

Since 1951, the U.S. Geological Survey (USGS) has made geochemical reference materials (GRMs) — well-characterized samples that give USGS researchers, industry, universities and other agencies a benchmark for quality control and experiments. The USGS Mineral Resources Program's reference materials project and the Energy Resources Program's petroleum geochemistry lab have teamed up to collect GRMs of source rocks from major U.S. petroleum systems, to support analysis of organic-rich mudrocks worldwide.

ShBOQ-1

ShBOQ-1 comes from the Upper Cretaceous Boquillas Formation in southwest Texas. It suits studies of source rocks rich in carbonate minerals and in oil-prone, sulfur-rich marine organic matter, and resembles the lower Eagle Ford Shale, a major South Texas petroleum play.

• Collection: about 720 kilograms of rock were taken in 2015 from a road cut about 20 miles west of Comstock, Texas, on State Highway 90; 360 kg were processed into ShBOQ-1.
• Two versions: finer than 0.074 mm for lab analysis and finer than 4 mm for well-site studies; the data apply to both.

Early "ShBOQ-proto" material: rock powder, pressed pellets, cutting-size chips and a slab. USGS / Stephen A. Wilson, 2016.

How it was tested

Commercial, academic and government labs tested it for major and trace elements, total organic carbon (TOC), programmed pyrolysis (such as Rock-Eval), and X-ray diffraction (XRD) mineralogy.

• Elements: an international study by the International Association of Geoanalysts, with 99 labs, showed the material is homogeneous — so spread in the results reflects the analyses, not the rock. A USGS contract lab ran fourteen replicates per method, consistent with that study.
• Organic geochemistry: labs measured TOC by combustion and infrared analysis, and ran several pyrolysis instruments on the same standard temperature program. Outliers were removed repeatedly using the interquartile range until all values fell within average ± 1.5 × IQR.
• Mineralogy: matters for planning drilling and hydraulic fracturing in unconventional plays.

Key results

Full datasets are in the accompanying USGS data release (Birdwell and Wilson, 2021).

Sources

Based on Geochemical and Mineralogical Properties of Boquillas Shale Geochemical Reference Material ShBOQ-1, U.S. Geological Survey Fact Sheet 2021–3048, by Justin E. Birdwell and Stephen A. Wilson, USGS Publications Warehouse; a work of the United States government in the public domain. Photographs and table values recovered from the fact sheet's PDF.