ABSTRACT: Petroleum Potential of the Basin and Range Province, Western United States

Norman H. Foster, Richard R. Vincelette

All production to date in the Basin and Range province has been found in extensional fault-block traps. The top seal is the base of the Tertiary valley-fill sequence, under which various reservoir units subcrop. Side seals are either faults or impermeable units. Oil source rocks include the Tertiary Sheep Pass Formation, Mississippian Chainman Shale, the Ordovician Vinnini Formation, and possibly other Tertiary-Cretaceous freshwater deposits and other Paleozoic units west of the Roberts Mountains thrust. Reservoirs range in age from Tertiary to Paleozoic, have lithologies ranging from ignimbrites to dolomite, and most are highly fractured with some having matrix porosity.

Shell Oil Company made the first discovery on the east side of Railroad Valley, Nevada, in 1954 at Eagle Springs field. This field has produced 3921441 bbl through June 1989 from fractured Tertiary ignimbrites and fractured and porous freshwater carbonates. In 1976, Northwest Exploration found Trap Spring field, which has made 7906235 bbl through June 1989 from Tertiary fractured ignimbrites. Grant Canyon field, discovered in 1983 by Northwest, also produces from a fault-block trap. The reservoir, however, is Devonian Guilmetter fractured dolomite with some matrix porosity, and has yielded 10881574 bbl through June 1989. The two wells in the field average over 6000 bbl a day, and represent some of the best daily production in the United States Kate Spring field in Railroad Valley was iscovered by Evans in 1986 and has several wells producing from Paleozoic carbonates.

Oil has also been found in similar traps in Pine Valley, Nevada, located about 100 mi northwest of Railroad Valley. Several fields have been discovered from fault-block traps, most notably the Blackburn field found by Amoco in 1982. Although the volcanics are tight at Blackburn, the sands within the Chainman and Devonian carbonates are good reservoirs.

Significant potential remains in fault-block traps similar to established production, as well as in folded and thrusted structures currently being explored.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990