A new report by the U.S. Geological Survey (USGS) shows an overall slightly improved outlook for unconventional natural gas potential in five “priority” Rockies basins.

The estimates of unconventional resources are part of just-completed assessments of all undiscovered, technically recoverable oil and natural gas resources in the Uinta-Piceance Basins of Colorado and Utah, the Southwestern Wyoming area (Greater Green River Basin), San Juan Basin of New Mexico and Colorado, Montana Thrust Belt, and the Powder River Basin of Wyoming and Montana.

Overall findings in the assessment indicate a mean of about 183 Tcf of undiscovered gas, of which 92% (a mean of 169 Tcf) of the undiscovered gas resource is unconventional; an indication that unconventional resources contribute significantly to the total of the estimated U.S. oil and gas — much more so than conventional resources in the five basins.

Of the 169 Tcf of unconventional gas, the report calculates about 25% (42 Tcf) is coalbed gas. The 2002 mean estimates for all undiscovered natural gas, oil, and natural gas liquids are:

Of particular interest is the mean estimate of 14.3 Tcf of coalbed gas in the Powder River Basin (Wyoming), a substantial increase from 1.1 Tcf in the continuous gas numbers from the last assessment made by the USGS in 1995. The increased estimate is based upon new geologic information from increased exploration and drilling operations.

While the Powder River Basin showed the greatest increase in undiscovered resources from the 1995 tally, the San Juan Basin totals also jumped from about 28 Tcf to 50 Tcf, while the Southwest Wyoming area dropped from about 119 Tcf to about 85 Tcf. The Uinta-Piceance Basins were about the same, near 21 Tcf, while the Montana Thrust Belt went from about 2 Tcf to 8.5 Tcf.

The assessment is part of a scheduled update of the USGS 1995 National Oil and Gas Assessment. USGS has decided to make the results available as they are completed in the different areas. The agency has identified the 25 largest basins to be studied. Next up are the Wind River and Big Horn Basins and the Wyoming Thrust area, and the Eastern Great Basin in Nevada. These should be completed in a couple years, according to Project Chief Chris Schenk.

Schenk notes the agency’s latest data is based on “more geologic data for all the areas, better well production data” and improved methodologies in aggregating the data. The new techniques have provided the USGS with “refined capabilities of understanding the resource potential, particularly unconventional resources, the agency announcement said.

The 2002 National Oil and Gas Assessment provides estimates of undiscovered conventional and unconventional hydrocarbon resources — not be confused with hydrocarbon reserves, which are resources that have been discovered and proven to be recoverable.

Conventional resource accumulations are discrete fields with well-defined hydrocarbon water contacts, have obvious seals and traps, and the hydrocarbon is buoyant upon a column of water. Unconventional or continuous accumulations are regional in extent, have diffuse boundaries, do not have obvious seals and traps, and are not buoyant upon a water column.

Detailed fact sheets of each basin are available at https://energy.cr.usgs.gov/oilgas/noga/

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