EXPLORATION AND PETROLEUM GEOLOGY OF THE CENTRAL UTAH HINGELINE

The central Utah “Hingeline” has seen cycles of petroleum exploration for the past 50 years because explorationists viewed the geology as a natural extension of productive thrust belt-style structures in northern Utah. Early unsuccessful efforts tested anticlines identified from surface mapping and seismic reflection data. The lack of a Cretaceous source seemingly was to blame for these failures.

The 2004 discovery of Covenant oil field proved the Hingeline does contain the right components (trap, reservoir, seal, source, and migration history) for large accumulations of oil. Exploration is focused on the Navajo Sandstone within Paleozoic-cored blind thrusts east of the Charleston-Nebo and Pavant thrusts, which formed during the Sevier orogeny. Likely targets include anticlines associated with thrust imbricates (or imbricate fans) and possible antiformal stacks of horses forming duplex structures in the Navajo and other potential reservoirs. These features are complicated by post-Sevier geology (Basin and Range extensional structures and Tertiary-Quaternary cover).

Covenant field has already produced over 2.4 million barrels of oil. The trap is an elongate, symmetric, northeast-trending anticline bounded on the east by a series of splay thrusts in a passive roof duplex. The Navajo reservoir, comprising a variety of eolian facies, is effectively sealed by 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. A thorough understanding of all the components that created Covenant field will determine if it is a harbinger of additional, large oil discoveries in this vast, under-explored region.