Covenant Oil Field, Central Utah Thrust Belt: Possible Harbinger of Future Discoveries

Chidsey, Thomas C.¹, Michael D. Laine¹, John P. Vrona², Douglas K. Strickland² (1) Utah Geological Survey, Salt Lake City, UT (2) Wolverine 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. To date, 10 producing wells and one dry hole have been drilled from two surface pads. Covenant has produced over 2 million bbls of oil and no gas; the field averages 6400 BOPD.

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 Jurassic 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 1600-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.