History and future of oil exploration in the Great Basin
Abstract
About 800 wildcats have been drilled in the Great Basin since 1900. This has resulted in the discovery of 21 fields and sub-commercial accumulations for a 2.5% success rate. A wide variety of reservoirs have been established, including: Paleozoic limestone, sandstone, and dolomite; Tertiary limestone, sandstone, welded tuff, and landslide breccia. Source rocks include Devonian and Mississippian shales, and various Tertiary continental deposits. For the first 45 years wildcatting was limited to a few wells per year, and drilling was mainly associated with surface seeps or water-well shows. A few wells were located based on the anticlinal theory, and most were drilled by independent operators. After World War II the pace of exploration increased, with 5 to 15 wildcats being drilled per year. During this time major oil companies tested large surface anticlines in the region. The first commercial discovery was made in 1954 by Shell Oil at Eagle Springs in Railroad Valley. The discovery marked a transition from drilling surface anticlines to exploration of the basins using geophysical methods. Sagging commodity prices and lack of success following the Eagle Springs discovery caused a slump in wildcatting during the early 1970s, but the Trap
Spring discovery in late 1976 coupled with rising oil prices again created incentive for exploration. During this time the Railroad Valley model evolved which identifies prospects in terms of proximity to generation sites in time and space. Discoveries made during 1980-2000, including Bacon Flat (1981), Blackburn (1982), and Grant Canyon (1983), were based to some degree on this model. At the same time successful exploration in the Utah-Wyoming Thrust Belt provided incentive for exploration for large thrust-
fault
related structures in the region as well. Following the discovery of Ghost Ranch field in 1996, exploration drilling activity collapsed and by 2010 had reached pre-World War II levels of fewer than 5 wildcats per year. The collapse may be related to the boom in resource play drilling which drained capital from conventional high-risk exploration. In recent years attempts have been made to develop unconventional reservoirs in Railroad Valley and Elko County. Resource plays have the potential to fundamentally change the future of exploration in the region. Development of a resource target will necessarily result in the evaluation conventional traps that might otherwise not get attention.
AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016