Calculation of Texas Lignite Resources Using the National Coal Resources Data System

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1996

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Calculation of Texas lignite resources, according to U.S. Geological Survey (USGS) methodology, using the National Coal Resources Data System (NCRDS) and software, began in 1979 and is now complete with reporting here of resources in three new regions—Jackson-Yegua east, Jackson south, and Wilcox south. In these regions, site files containing well locations and total lignite thicknesses were created using Ingres, a relational database software. Resources were calculated using the Geographic Resources Analysis Support System (GRASS) GIS. Texas lignite resources were calculated from a database of 4,700 density and lithologic logs in terms of three USGS thickness categories (2.5 to 5 ft, >5 to 10 ft, and > 10 ft) and one Bureau of Economic Geology (BEG) category (≥3 ft). NCRDS resources, calculated using USGS methodology, total 46,979 million tons, of which 15,767 million tons (34 percent) are demonstrated resources. Most of them are in beds 2.5 to 5 ft thick. Two-thirds of the resources are in the Wilcox trend and one-third in the Jackson-Yegua trend. The state's richest lignite regions are Jackson-Yegua east and Wilcox east-central. In a comparison of NCRDS and BEG resource estimates, made using the same database and thickness category (≥3 ft), the USGS inflated inferred resources, whereas the BEG, using geologic models, constrained inferred resources and maximized demonstrated resources, which are 13,691 and 20,383 million tons, respectively. The USGS method is highly data dependent and can make no allowance for demonstrated resources as defined and estimated by the BEG with moderate certainty using geologic models. The computerized and geologic methods could be combined to improve resource estimates from limited data.

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