SPEAKER: Mr. Jerry Walker, Consultant (Retired)
TOPIC: 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 1930’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.)
Nevada oil fields are anomalous compared to many conventional hydrocarbon accumulations. A review of the petroleum systems (i.e., hydrocarbon kitchen and container, plumbing, and timing) of Nevada’s four largest oil fields can illuminate these disparities. A fundamental difference is that in most mature oil-producing basins, exploration is focused on the hydrocarbon container, as generation of oil and gas in the hydrocarbon kitchen, the plumbing that controls the migration of the hydrocarbons from kitchen to container, and timing of generation, migration, and trap formation are no longer issues; however, in the Great Basin, exploration is driven by the hydrocarbon kitchen. Prospects are built first by identifying where source rocks are generating oil, and then by defining the trap, reservoir, and seal.
Grant Canyon Oil Field is Nevada’s largest. Two of its wells, the #3 and #4 Grant Canyon, are renowned for reportedly being the largest onshore oil producers in the lower 48 states from 1984 to 1991. However, the #10 Grant Canyon is the field’s Cinderella well. It was completed as a dry hole in 1993, despite coming in structurally tied as the second highest well in the field. Today, it is Nevada’s largest producing oil well, with the oil coming from the same reservoir that tested hot, fresh water in 1993.
Exploration methods used to identify potential hydrocarbon containers rely on reflection seismic, gravity, and surface geochemistry. However, all of these methods suffer serious deficiencies. Reflection seismic cannot adequately image the complex structure in the Tertiary volcanics and Paleozoic sedimentary section. Gravity and surface geochemistry do not provide adequate resolution to clearly define potential traps. None seem capable of evaluating the quality of reservoir and seal for a possible trap.
Any strategy for overcoming these challenging conditions must improve our ability to identify likely hydrocarbon containers. To do so, exploration should focus on areas with the potential for high quality reservoirs and seals by considering: 1) geothermal activity that can enhance oil generation, reservoir porosity, and lateral and top seals; 2) low-angle detachment faulting that can increase the likelihood of large blocks of highly permeable reservoir rock; and, 3) en echelon faulting that can form open fractures within a potential reservoir block, providing high permeability as well as promoting deep circulation of groundwater to depths sufficient for heating to moderate geothermal temperatures. Furthermore, new tools must be developed to better image and locate varied traps with quality reservoirs and seals.
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.
BIOGRAPHY: Jerry is a retired geologist with 41 years of experience in the oil patch exploring for and producing hydrocarbons. He branched out into geothermal during the last six years. Jerry has been employed as a geologist, geophysicist, engineer, landman, and manager for companies as large as Texaco and as small as a sole proprietorship. Since 1993 he has consulted in the Basin-and-Range Province, California, Colorado, Utah, Idaho-Utah-Wyoming thrust belt, Venezuela, Mexico, Hungary, Indonesia, Bangladesh, and the Gulf of Thailand. He graduated from Indiana University in 1972 with a B.S. in Geology and the University of Illinois in 1975 with an M.S. in Geology. Jerry has served as president of the Nevada Petroleum Society and the Rocky Mountain Section of the American Association of Petroleum Geologists, general co-chair of 2005 Rocky Mountain Section–AAPG and 2016 AAPG–Pacific Section–Rocky Mountain Section conventions, and director of the Rocky Mountain Section–AAPG Foundation.
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