Structure, Stratigraphy, And Hydrocarbon Potential of Butte
Valley, White Pine County, Nevada
Alfred H. Pekarek, Dept. of Earth
& Atmospheric Sciences, St. Cloud State University, MS 47, 720 Fourth Ave.
S, St. Cloud, MN 56301, phone: 320-308-4127, fax: 320-308-4262,
[email protected]
Butte Valley in east-central Nevada
occupies a tectonic transition zone between the weakly deformed Butte Mountains
on the west and a strongly deformed core complex to the east. East-central
Nevada underwent compressional tectonism in the Paleozoic and in the Mesozoic and
extensional tectonism in the Cenozoic. Consequently
it contains both compressional and extensional
structures favoring the development of a variety of hydrocarbon traps. An
essentially complete Paleozoic section (Permian strata are missing locally)
exceeds 20,000 feet of predominantly carbonate strata. A relatively thin
Tertiary cover (commonly only a few thousand feet thick) includes Oligocene volcanics and younger valley fill sediments. Source rocks
include nearly 2000 feet of the Mississippian Chainman Shale, the primary
petroleum source rock in east-central Nevada,
the Pilot Shale and some organic-rich carbonates. Published geochemical data
from well cuttings show the Chainman to be in the oil generating window.
Multiple carbonate reservoirs with solution enhanced fracture porosity are the
primary objectives. Paleozoic sandstones and Tertiary volcanics
provide secondary objectives. Gravity data and detailed photogeologic
mapping allows Butte
Valley to be subdivided
into 5 areas, each with unique geologic features. The northern areas appear
less prospective than the southern areas. Residual gravity data suggest a
variety of potential hydrocarbon traps, including reentrants and horsts. Photogeologic mapping suggest domal
traps under the valley fill adjacent to the Butte
Mountains and fault block traps
adjacent to the Eagan
Range. Geochemical data
(primarily soil gas) indicate some of these traps may contain accumulations of
hydrocarbons.