Integrated Reservoir Characterization of the Entrada Erg-margin Gas Play, Utah: An Outcrop and Seismic Analog for the North Hill Creek/Flat Rock Field, Southern Uinta Basin, Utah

Thomas H. Morris, Department of Geology, Brigham Young University, S381 ESC, Provo, UT 84602, phone: (801)378-3761, [email protected], Will Monn, Department of Geology, Brigham Young University, S 371 ESC, Provo, UT 84602, John H. McBride, Department of Geology, Brigham Young University, S 371 ESC, Provo, 84602, and R. William Keach, II, Landmark and Brigham Young University, Houston, TX 77042.

Recent discovery of high-BTU gas-charged Jurassic reservoirs in the North Hill Creek/Flat Rock (NHC/FR) Field, southern Uinta Basin, Utah, have ignited interest in below-Tertiary reservoirs within the basin and other areas of Utah. Erg-margin rocks of the Jurassic Entrada Sandstone are of particular interest because of their potential to contain large, high quality reservoirs and develop stratigraphic traps. Entrada erg-margin sandstones exposed along the east flank of the Waterpocket Fold, south-central Utah, appear to be isolated sandstone bodies enveloped within the tidal flat “earthy” facies. Tidal flat facies are dominated by mudstones and siltstones. These outcrops are likely analogs for reservoirs in the NHC/FR Field.

Outcrop and log analyses are integrated with seismic attribute maps of the Entrada section from a 3D seismic survey acquired by Wind River Resources over the NHC/FR Field. Relative to important reservoir considerations, our study indicates: 1- eolian-influenced facies have porosities greater than 23 percent, 2- water table fluctuations during dune development affect reservoir quality, and 3- erg-margin, reservoir quality sandstone bodies can be offset vertically and isolated from each other.

Reservoir characterization studies of the outcrop include; photomosaics, identification of facies and potential baffles and barriers, porosity/permeability analysis, sedimentary petrology, grain size analysis, and measured sections including scintillometer logs. Strike- and dip-oriented, high resolution 2D seismic reflection profiles were shot in an attempt to understand the 3D architecture of