Detailed Stratigraphy and Hydrocarbon Potential of the Devonian-Mississippian Pilot Shale, Western Utah, U.S.A.

Abstract

Detailed stratigraphic examination and extensive sampling of a ~1000-ft-thick surface section of the Devonian-Mississippian Pilot Shale from the Confusion Range in western Utah demonstrates clear potential for hydrocarbon production. Total organic carbon measurements from dark gray, calcareous and noncalcareous mudrocks, particularly in the lower parts of the formation, range from 1.4 to 2.4 wt.%, and Tmax values fall mostly in the oil potential window (438–449°F). The Pilot could be gas-productive elsewhere as a result of commonly recognized hydrothermal activity in both Nevada and Utah.

Overall, the Pilot Shale in Utah is heterogeneous, as the mudrocks are stratigraphically admixed with calcareous siltstones, micritic to organic limestones, occasional red beds, and fine-grained sandstones. The Pilot is representative of an offshore and locally deep basinal setting influenced by tectonic activity of the Antler orogen in central Nevada. The Pilot in this locality progressively shallows upward in an oscillatory fashion toward the overlying shelfal Mississippian Joana Limestone. The shallowest deposits in this section consist of distinctive red beds and oncolitic limestones. A near-complete surface gamma-log transect substantiates this overall trend and provides a valuable correlation to a nearby subsurface penetration, and possibly to future wells. Based on both lithologic and biostratigraphic conclusions involving previous conodont work, the lower Pilot is a clear facies equivalent to the Devonian Guilmette Formation and to its formational equivalents elsewhere. The upper Pilot is a lateral equivalent to shallow-water restricted carbonates and clastics, exposed both to the east and south (e.g., Pinyon Peak Limestone, Victoria Peak Quartzite, Fitchville Formation). Parenthetically, the Pilot is exceedingly variable in other sections measured to the west (Nevada), but these sequences also reveal potential for an unconventional hydrocarbon resource.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018