Print this pageAbstract: Geologic Techniques Used in Trap Spring Field Discovery, Railroad Valley, Nye County, Nevada
The geologic and geophysical criteria used to discover the Trap Spring field developed as a result of a thorough understanding of the Eagle Springs field, Nye County, Nevada.
The most prolific reservoirs in the field are the Oligocene Garrett Ranch fractured ignimbrites and the Eocene Sheep Pass Formation. These reservoirs are truncated by an unconformity and overlain and sealed by the Horse Camp Formation. Organic-rich lake beds in the Sheep Pass Formation were believed to be the source of the low-gravity, high-pour-point crude oil at Eagle Springs. These truncated beds are on a down-faulted block along the basin margin. The key to our success was the recognition that production is from the updip corner of the lowermost fault block along the major basin margin fault. To localize traps, geomorphology can be used to identify (1) the major boundary fault, (2) cross faults, and (3) structural noses extending into the basin, and thereby locate the position of he most downthrown block. On a seismic line across the Eagle Springs field it was easy to identify the truncated Sheep Pass and Garrett Ranch volcanic rocks. The Horse Camp Formation was deposited on this unconformable surface.
Prior to our exploration effort, dry holes were drilled in several of the valleys in the Basin-and-Range province. Most encountered bald Paleozoic highs. None of the wells were drilled on features that had the characteristics essential for an Eagle Springs-type accumulation.
The exploration approach was: (1) map the distribution of Sheep Pass reservoir and source-rock facies and the Garrett Ranch volcanic reservoir facies; (2) identify Eagle Springs-type geomorphic anomalies; (3) shoot high-quality seismic data to identify the stratigraphic units and map truncations; and (4) drill the best looking features, especially those updip from shows.
The second well in the program was the discovery well of the Trap Spring field. Approximately 1,200 BOPD was pumped from fractured Garrett Ranch volcanic rocks on a downfaulted truncation trap sealed by the Horse Camp Formation.
AAPG Search and Discovery Article #90964©1978 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah