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Abstract: A Precambrian-Cambrian Oil Play in Southern Utah

P. G. Lillis, J. G. Palacas, A. Warden

The potential of the Precambrian Chuar Group as a petroleum source rock in southern Utah and northern Arizona resulted in the drilling of two wildcat wells in 1994. Both wells penetrated the Cambrian Tapeats Sandstone (the target reservoir rock) and presumably Precambrian rocks. The first well, Burnett Federal 36-1, was drilled east of Kanab, Utah (sec.36, T.34S., R.3W.) to a total depth of 5,365 ft and encountered Precambrian (?) reddish-brown sedimentary rocks at 4,790 ft. The Tapeats Sandstone had live oil shows and minor CO2(?) gas shows. The second well, BHP Federal 28-1, was drilled near Capitol Reef (sec.28, T.33S., R.7E.) to a total depth of 6,185 ft and encountered the Tapeats Sandstone at 5,922 ft and Precambrian(?) phyllite at 6,125 ft. The upper Pal ozoic rocks had abundant live oil/tar shows, and the Cambrian Bright Angel Shale and Tapeats Sandstone had numerous oil shows. There were no gas shows in the well except for a large CO2 gas kick in the Tapeats Sandstone. A drill-stem test from 5,950 to 6,185 ft yielded mostly CO2 (92%) and nitrogen gas (6%) and minor amounts of helium, argon, hydrogen, and methane. The ^dgr13C of the CO2 is -3.9 per mil PDB. The chemical composition of the extracted oil in the Cambrian sandstones is significantly different than oils produced from the Upper Valley field (upper Paleozoic reservoirs) and the tar sands that are widespread throughout southern and central Utah. However, the oil composition is similar in several aspects to the composition of some of t e Precambrian Chuar Group bitumen extracts from the Grand Canyon area in Arizona. The encouraging features of both wells are the good reservoir characteristics and oil shows in the Tapeats Sandstone. In the BHP well the oil appears to be a new oil type, possibly derived from Precambrian or Cambrian source rocks.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada