How the USGS Assesses U.S. Coal Resources and Reserves

From a U.S. Geological Survey fact sheet on the U.S. Coal Resources and Reserves Assessment Project, 2017.

The U.S. Coal Resources and Reserves Assessment Project, part of the USGS Energy Resources Program, carries out systematic, geology-based regional assessments of the significant coal beds in the country's major coal basins. They describe how much coal remains, its quality, where it is and whether it can be mined at a profit — objective information for energy strategy, environmental policy, land management and economic forecasting.

Why assess coal

The U.S. Energy Information Administration projected that about 30 percent of the country's electricity would come from coal over the following several years, and that coal would remain a major fuel for power generation for the foreseeable future. That coal lies in many beds and zones of differing thickness, rank, extent and quality in coal fields across the country. Knowing whether it can meet future demand requires regular, objective assessments.

Coal fields of the conterminous United States (modified from East, 2013). USGS.

Resources are not reserves

The United States has vast coal resources, but only a small percentage of them are reserves. The two words are often used as if they meant the same thing; the USGS, adapting its Circular 891, defines them differently:

• Coal resources are natural deposits of coal in the Earth's crust in amounts that make economic extraction currently or potentially feasible.
• Coal reserves are the part of the recoverable resources that can be mined economically at the time they are classified, even if the mining facilities are not yet built or running.

Resources are narrowed step by step, each step subtracting coal lost to past mining, geology, environmental limits or mining technology. Whether recoverable coal counts as a reserve changes over time with mining costs and the price of coal: to be economic, the coal's market value must exceed the cost of extracting it, which the USGS estimates with economic models based on regional mining practice and prefeasibility costs.

The Powder River Basin shows how much the numbers shrink:

Estimating recoverable resources and reserves gives a far more realistic picture of the coal actually available to mine with current technology.

What is new about these assessments

The project assesses the country's remaining coal, and the recoverable resources and reserves in individual significant coal beds — beds extensive and thick enough to warrant assessment — in the major provinces and regions. Unlike earlier USGS coal assessments, current ones:

• report tonnages for every resource category as well as reserves, not just total or remaining resources;
• cover basins or coal fields within basins, rather than areas ranging from whole regions down to single 7.5-minute quadrangles;
• focus on individual significant coal beds rather than zones containing several beds.

Where the work is

The current focus is the Northern Great Plains and Rocky Mountain coal provinces, with an emphasis on coal under federal land.

• Powder River Basin, Wyoming and Montana: the first basin assessed bed by bed.
• Greater Green River Basin, Wyoming and Colorado: the second, in three areas — the Little Snake River coal field and Red Desert (south-central Wyoming), the Yampa coal field (northwestern Colorado) and the Rock Springs uplift (southwest Wyoming). It was chosen because it holds large tracts of federal land — about 58 percent of the surface in the Little Snake River and Red Desert area — and much of it had never been formally assessed for coal. Much of the drill-hole data behind the new models was collected by the USGS within the previous five years.
• Under consideration: the Raton and Piceance basins in the Rocky Mountain Province and the Williston Basin in the Northern Great Plains; and the Illinois Basin, the northern Appalachian Basin and the Gulf Coast Province, which will keep supplying large amounts of U.S. coal.

Current assessment areas in the Greater Green River Basin. USGS.

How it is done

The method, peer-reviewed and based on established USGS practice, has three phases:

1. Data collection: geologic, coal-quality, restriction and economic data are gathered and organised.
2. Data modelling: significant coal beds are correlated and modelled.
3. Calculations: the geologic and economic models are evaluated, and resources and reserves calculated.

The USGS shares data, correlations and interpretations with federal and state agencies, including state geological surveys and the Bureau of Land Management. The results are used by universities, industry and many federal and state agencies.

Sources

• U.S. Geological Survey, Assessing U.S. Coal Resources and Reserves, Fact Sheet 2017–3067, by the U.S. Coal Resources and Reserves Assessment Project (Brian N. Shaffer, Jon E. Haacke, David C. Scott, Paul E. Pierce, Scott A. Kinney, Ricardo A. Olea and James A. Luppens). https://doi.org/10.3133/fs20173067 — the Powder River Basin table and two maps recovered from the PDF.
• The Powder River Basin figures are from Luppens and others (2015); the fact sheet also cites Rohrbacher and others (2005) and Wood and others (1983).
• Rewritten in hubnx's own words.