Hydrocarbon potential of arkosic sands in the Payette Basin, southwest Idaho: a discussion on basin fill, subsurface structure, and syndepositional maturation and migration history

Abstract

Miocene-Pliocene arkosic sandstone and mudstone deposits in the Payette Basin of southwest Idaho are derived dominantly from the Idaho Batholith and provide several unconsolidated to slightly consolidated fine to coarse sand stacked reservoir intervals for the natural gas and liquid condensate play. Other unique interbedded lithologies within the lacustrine and fluvial depositional system are tuffaceous and bentonitic intervals, rhyolitic and basaltic dikes and flows, and large deposits of evaporitic rocks. Recent analyses of well cuttings place the subsurface deposits in the Glenns Ferry, Chalk Hills, and Poison Creek formations of the Idaho Group. The middle Miocene Payette and Succor (Sucker) Creek formations may be present beneath the basal volcanic interval where the majority of the wells TD but is usually not penetrated because it lies in the poorly imaged and understood ‘Miocene acoustic basement’. Possible localized hydrocarbon source beds are exposed near Horseshoe Bend and a previous total organic carbon analysis report (Geochem Laboratories Report, 1981) indicates adequate organic content is present surficially but are undermature and are in the pre-peak oil generation window. These organic-rich surficial units project southward into the Payette Basin and may contribute to the hydrocarbons produced from conventional wells. Under higher geothermal regimes, more liquid condensate and an addition of liquid hydrocarbons is possible. In this study x-ray diffraction, clay, and petrophysical analyses help delineate significant sedimentary packages and highlight the interplay between clastic deposition and coeval volcanic rocks. Simplified depth-structure maps and isochores derived from well tops show a relative deepening and thickening of basin sediments in the northwest part of the basin. A detailed examination of the kerogen and palynomorph samples collected from surficial sediments north of the producing fields also show thermally immature indicators relative to hydrocarbon generation which is congruent and comparable to the geochemical report from Horseshoe Bend (Staplin, 1969; 1977) and Palynomorph Darkness Index (Goodhue & Clayton, 2010 Palynology Vol. 34, No. 2). Down-to-basin normal faults appear to provide structural controls for hydrocarbon-bearing sandstones. More exploration is needed to assess adequate hydrocarbon source, and the maturation and migration history in the basin. Other older organic-rich sedimentary rocks also occur in southern Idaho and may also contribute to the hydrocarbons of the Payette Basin.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016