Covenant Oil Field, Central Utah Thrust Belt: Possible Harbinger of Future Discoveries
Laine, Michael D.1, Thomas C. Chidsey1, Douglas A. Sprinkel1,
John P. Vrona2, and Douglas K. Strickland2
1Utah Geological
Survey, Salt Lake City, UT
2Wolverine Gas and Oil
Corporation, Grand Rapids, MI
After over 50 years of exploration in the central Utah thrust belt,
or “Hingeline,” the 2004 discovery of Covenant oil field proved that
this region contains the right components (trap, reservoir, seal,
source, and migration history) for large accumulations of oil.
Covenant has produced over 3 million bbls of oil and no gas from the
Jurassic Navajo Sandstone; the field averages 5500 BOPD. The OOIP
is estimated at 100 million barrels; the estimated recovery factor is 40
to 50%.
The Covenant trap is an elongate, symmetric, northeast-trending
anticline, with nearly 800 ft of structural closure and bounded on the
east by a series of splay thrusts in a passive roof duplex. The eolian
Navajo Sandstone reservoir is effectively sealed by mudstone and
evaporites in the overlying Jurassic Twin Creek Limestone and
Arapien Shale. Oil analysis indicates a probable Mississippian source
– oil derived and migrated from rocks within the Hingeline region.
Cores from the Navajo Sandstone display a variety of eolian facies
(dune, interdune, lake/playa, fluvial/wadi), fracturing, and minor
faults which, in combination, create reservoir heterogeneity.
Reservoir sandstone is 97% frosted quartz grains (bimodal grain size),
with some quartz overgrowths and illite. The net reservoir thickness
is 424 ft over a 960-ac area. Porosity averages 12%; permeability is
≤100 mD. The drive mechanism is a strong water drive; water
saturation is 38%. A thorough understanding of all the components
that created Covenant field will determine whether it is a harbinger of
additional, large oil discoveries in this vast, under-explored region.
AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah