The Chuar Petroleum System Revisited
The Neoproterozoic Chuar Group consists of marine mudstone, sandstone and dolomitic strata divided into the Galeros and Kwagunt Formations; the sequence is exposed only in the eastern Grand Canyon, Arizona. Research by the U.S. Geological Survey (USGS) in the late 1980s recognized strata within the group to be possible petroleum source rocks, and in particular the Walcott Member of the Kwagunt Formation. Industry interest in a Chuar oil play led to four exploratory wells drilled in the mid-1990s in southern Utah to test the overlying Cambrian Tapeats Sandstone reservoir, and confirm the existence of the Chuar in subcrop. Geochemical analyses by the USGS of Tapeats oil shows in two wells suggest that the Chuar may be the source of the shows, but the correlation is tentative. Distribution of the Chuar in the subsurface is poorly constrained, with one outcrop and five well penetrations, but recently published gravity/aeromagnetic interpretations provide further insight into the Chuar subcrop distribution. The Chuar petroleum system was reexamined as part of the USGS Paradox Basin resource assessment effort in 2011. A map was constructed to delineate the Chuar petroleum system that encompasses the projected Chuar source rock distribution and all oil shows in the Tapeats Sandstone, assuming that the Chuar is the most likely source for such oil shows. A total petroleum system map was constructed based on the assumption that oil generation in the Chuar occurred in the early Tertiary and migrated into existing Laramide-age traps. Two hypothetical plays were recognized but not assessed: a conventional play with a Chuar source and Tapeats reservoir, and an unconventional play with a Chuar source and reservoir. The conventional play has been tested by drilling with no success thus far, but the unconventional play is untested.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012