Origin and nature of the hydrocarbon seal in Railroad Valley, Nye County, Nevada

Conference · Sun Aug 01 00:00:00 EDT 1993 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:6705686

French, D E ^[1]; Hulen, J B ^[2]

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1. Independent Geologist, Billings, MT (United States)
2. Univ. of Utah Research Institute, Salt Lake City, UT (United States)

Over 33 million bbl of oil have been produced from the Basin-Range oil fields of Railroad Valley in eastern Nevada. Oil-reservoir rocks are Devonian to Tertiary age, forming structural or structural/stratigraphic traps beneath a widespread seal at the base of an alluvial and lacustrine, Miocene-Pliocene valley-fill sequence. This seal is mandated by Railroad Valley drilling results to date: sub-valley-fill strata are oil rich, but of 850,000 ft of valley fill penetrated by 214 wells, fewer than 150 ft have yielded oil shows. Temperatures from drill-stem tests also indicated that the seal commonly coincides with a thermocline. The nature and origin of the seal have been investigated at Bacon Flat and Grant Canyon fields in east-central Railroad Valley, and in nearby Horse Camp basin where a contemporaneous valley-fill sequence is exposed. At all three sites, the basal valley fill consists of tuffaceous clastic rocks in which volcanic ash has been altered to montmorillonite. At the two oil fields, these clay-rich rocks have also been hydrothermally kaolinized and silicified, enhancing the permeability barrier at the unconformity. The sealed zone and associated thermocline could affect the thermal regime of the basin, and thereby the size and distribution of potential hydrocarbon generation sites; they could mask the presence of commercial geothermal systems. Improved understanding of the sealing processes also could help constrain models of hydrocarbon-associated precious-metal deposits.

• OSTI ID: 6705686
• Report Number(s): CONF-930947-; CODEN: AABUD2
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 77:8; Conference: Rocky Mountain section meeting of the American Association of Petroleum Geologists (AAPG), Salt Lake City, UT (United States), 12-15 Sep 1993; ISSN 0149-1423
• Country of Publication: United States
• Language: English

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