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Updated Assessment of Undiscovered Continuous Tight Gas Resources in the Williams Fork and Wasatch Formations, Piceance and Uinta Basins, Colorado and Utah

Abstract

The U.S. Geological Survey (USGS) is currently assessing the undiscovered, technically recoverable tight gas resources using a geology-based assessment methodology for the interval from the base of the Upper Cretaceous Mesaverde Group through the Paleogene Wasatch Formation in the Piceance and Uinta Basins of Colorado and Utah. The Mesaverde Group was deposited in a coastal plain setting and the Wasatch Formation in a continental basin setting. Reservoir rocks are fluvial sandstones that are produced using directional drilling. The major source of gas are coastal plain coal beds and carbonaceous shale in the lower part of the Mesaverde Group. The Cameo coal zone in the Piceance Basin has total organic carbon contents as high as 70 weight percent. Over 9 trillion cubic feet of gas have been produced from the Mesaverde Group and Wasatch Formation in the Piceance and Uinta Basins. Gas in the Mesaverde Group was first discovered in the 1950’s from a vertical well in the Hunters Canyon Field. The first directional well to produce gas from the Williams Fork Formation was in 1991 in the White River Field of the Piceance Basin. Since that time, most tight gas production has been from directional wells. The continuous (unconventional) gas accumulations of the Mesaverde Group and Wasatch Formation in the Piceance and Uinta Basins, were previously assessed by the USGS in 2003 using 4 continuous assessment units (AUs). For the newly revised assessment, two continuous AUs were defined: (1) the Piceance Basin Mesaverde Tight Gas AU; and (2) the Uinta Basin Mesaverde Tight Gas AU. The AU boundaries extend to where vitrinite reflectance (%Ro) contours in coal source rocks are 0.75 percent or greater (indicating thermal maturity is in the gas window). The Piceance Basin Mesaverde Tight Gas AU now includes the previously defined Piceance Basin Continuous Gas AU and the Piceance Basin Transitional Gas AU. The Uinta Basin Mesaverde Tight Gas AU now includes the previously defined Uinta Basin Continuous Gas AU and the Uinta Basin Transitional Gas AU. These newly defined AUs, along with recent drilling and production data, will be used to quantitatively evaluate undiscovered, technically recoverable continuous tight gas resources from the base of the Mesaverde to the top of the Wasatch in the Piceance and Uinta Basins. Results are expected to be released in 2019.