What we know and wish we knew about oil exploration in Nevada

Abstract

Oil exploration in Nevada began in the early 20th century. Approximately 53 wells were spudded in the State between 1907 and January 1950. It is difficult to discern a play concept used to justify many of these wells. However, 12 wells were drilled in western Nevada in the 1920's based on shows of biogenic gas in water wells. Surface structures, such as the Illipah Anticline and Arden Dome, were tested in the 1920's and ‘30's. The deepest well during this time reached 5,218 feet beneath the featureless floor of Coaldale Marsh. It was reportedly located using a ‘Mansfield Patent Automatic Water and Oil Finder.’ Modern oil exploration in Nevada began in the mid 1950's with the first of three wells drilled by Standard Oil of California and Continental Oil. These wells were located by mapping surface anticlines defined by Paleozoic rocks. Although oil shows were reported, no production was established. It wasn't until 1954, when Shell Oil drilled their #1 Eagle Springs well in Railroad Valley, based on a seismically identified structural anomaly, that a producing oil well was discovered. Since then, 18 additional oil accumulations have been found, producing approximately 53 million barrels of oil. Drilling since 1950 has resulted in ~3% exploratory success rate (19 discoveries/~553 wildcat wells.) Of the critical limiting factors controlling hydrocarbon accumulations, Nevada is endowed with rich source rocks, highly permeable reservoir rocks capable of flowing thousands of barrels per day, and favorable structural configurations. But, it is lacking in high-quality seals, extensive generation sites, and favorable timing of trap development and oil migration. Although Nevada has experienced three major periods of deformation capable of trap formation and three episodes of hydrocarbon generation and migration, traps with the lowest risk are those closest to Miocene-Pliocene hydrocarbon kitchens. Exploration methods used to identify drillable prospects have routinely relied on reflection seismic data. Photogeologic, gravity, surface geochemistry, and rarely aeromagnetic data were also used to define prospects. However, all methods suffer serious deficiencies. Seismic cannot adequately image the complex structure in the Tertiary volcanics and Paleozoic sedimentary section. Photogeologic mapping is limited in its useful scope. Gravity, surface geochemistry and aeromagnetics may not provide the necessary resolution to clearly define potential traps. None seem capable of evaluating the quality of seal for a possible structural trap. Any strategy for overcoming these challenging conditions must improve the ability to recognize trapping configurations with lower risk. To do so, play concepts should focus on areas: 1) with geothermal activity that can enhance oil generation, reservoir porosity, and lateral and top seals; 2) of low-angle detachment faulting that can increase the likelihood of contiguous highly permeable reservoir rock; and, 3) of en echelon faulting that can develop open fractures within a potential reservoir block and promote deep circulation of geothermal groundwaters. In Nevada's Basin-and-Range Province, geology has conspired to create a continuum of environments favorable for the development of petroleum, geothermal, and precious-metal deposits and resources. Geologists exploring for oil in Nevada can benefit from strategies used in these two complementary disciplines in the search for new hydrocarbon accumulations.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016