Covenant Oil Field in the Central Utah Thrust Belt—What has Been Learned in the 15 Years Since the Discovery
The 2004 discovery of Covenant field in the central Utah thrust belt proved the region had the right components for major accumulations of oil. The field has since produced over 25 million BO (with no gas) from an elongate, symmetric, northeast-trending hanging-wall anticline on the east-verging Salina thrust fault. The discovery set off a frenzy of leasing, seismic acquisition, and drilling. However, additional discoveries of similar size to Covenant have remained elusive and the lack of success combined with depressed oil prices and the success of unconventional shale plays caused activity to essentially cease. Despite a drop off in activity, much has been learned over the past 15 years about Covenant’s stratigraphy, facies, hydrocarbon source, and migration history that can be applied to future exploration efforts in central Utah.
Initially, production was interpreted to be from the eolian Lower Jurassic Navajo Sandstone that included upper and lower intervals separated by a significant interdune barrier. From regional correlations, palynology, and detailed facies analysis, we now know that the interdune and upper interval is the Middle Jurassic Temple Cap Formation. The Navajo represents a Sahara-like erg whereas the Temple Cap was deposited as coastal dunes (White Throne Member) and sabkha and tidal flat environments (Sinawava Member, i.e., the barrier interval).
The Covenant oil is likely derived from a relatively local Carboniferous-age source on the nearby Aurora/Valley Mountain thrust plate. Primary migration occurred 90-100 Ma into a paleotrap. When the current Covenant trap formed 70-80 Ma, remigration stripped the original gas-saturated oil of volatiles, thus no gas is produced from the field.
In 2018, the operator, Wolverine Gas and Oil Corp., drilled and completed three wells on the south flank of Covenant field to evaluate the productive limits of the field. Future exploration in central Utah should focus on Paleozoic-cored, blind thrust structures associated with fault imbricates and duplexes positioned near back thrust and extensional faults, and subthrust traps. Potential reservoirs include the Navajo Sandstone and now the Temple Cap Formation, as well as the Permian Kaibab Formation, Triassic Sinbad Limestone, and key members of the Middle Jurassic Arapien Formation. The lack of any associated gas at Covenant field suggests the possibility that potential gas-charged traps may also be present in the region.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019