--> Abstract: Hydrocarbon Potential in the Grand Staircase-Escalante National Monument, Southern Utah, by T. C. Chidsey, Jr., D. A. Sprinkel, and M. L. Allison; #90928 (1999).

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CHIDSEY, T.C., JR., D.A. SPRINKEL, and M.L. ALLISON
Utah Geological Survey

Abstract: Hydrocarbon Potential in the Grand Staircase-Escalante National Monument, Southern Utah

The Grand Staircase-Escalante National Monument, which includes a large part of the Kaiparowits basin in southern Utah, contains all the necessary elements for oil and gas accumulations: reservoir rocks, source rocks, seals, and trapping mechanisms. Although the characteristics of the monument as a whole are favorable for the accumulation of oil and gas, wildcat well density is extremely low. Only 48 exploratory wells have been drilled within the monument, an average of 57 square miles per well.

Potential reservoirs in the monument are the Cambrian Tapeats Sandstone and Muav Limestone, Mississippian Redwall Limestone, Permian Kaibab Formation, and Timpoweap Member of the Triassic Moenkopi Formation. Potential source rocks include Precambrian, Cambrian, Mississippian, and Permian organic-rich strata. A recent study shows that the oil produced from Permian and Triassic reservoirs in the region are derived from organic-rich Permian source rocks (including the oil produced from Upper Valley field). Carrier formations and major faults can provide migration pathways through which oil and gas generated from these source rocks could have migrated into reservoirs and traps in the monument. Laramide-age, basement-cored surface anticlines observed within the monument are the potential traps. However, during the Pleistocene, changing hydrologic conditions shifted hydrodynamic drive to the southwest. The result was the displacement of oil from the crest of at least one structure and possibly others. The monument contains at least 24 major anticlines, many of them tens of miles long. Numerous subsidiary closures are likely to be present along these structures. Very few structures have been drilled off-crest so potential hydrodynamically displaced deposits remain largely untested.

Commercial deposits of oil were discovered in 1964 both within and along the margins of the monument an Upper Valley field. The Mississippian Redwall Limestone, Permian Kaibab Formation, and Timpoweap Member of the Triassic Moenkopi Formation are productive. Upper Valley field has produced 25,144,770 barrels of oil, ranking it as the ninth-largest oil field in Utah in terms of total production. There are 22 active wells in the field; five of these wells lie within the monument and accounted for nearly 27 percent of the field production in 1996, and 10 percent of the total cumulative field production. In total, the monument wells would be ranked as the eighteenth-largest field in Utah in terms of cumulative production.

The Cambrian Tapeats Sandstone is an ideal target for exploratory drilling. Only four wells have penetrated through the Cambrian Tapeats Sandstone and into Precambrian rocks on major anticlines in the monument; the most recent being Conoco's Reese Canyon State 32-2 well drilled in 1997. The BHP 28-1 Federal well drill-stem tested CO2 at an initial flow rate of 5.0 MMCFGPD from the Tapeats on the Circle Cliffs uplift. Possible source rocks for Tapeats reservoirs are the Proterozoic (Precambrian) Chuar Group of the Grand Canyon Supergroup below or the Cambrian Bright Angel Shale above. The Bright Angel also provides an effective seal Using Chuar source-rock volumetrics modified from a previous study and applying an entrapment rate of 10 percent in Cambrian Tapeats reservoirs, the oil in-place could be 270 million barrels or more within the monument.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas