|Fact Sheet 2005–3053: Text-Only Version|
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U.S. Department of the Interior
U.S. Geological Survey
Fact Sheet 2005-3053
Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 1.6 billion barrels of undiscovered oil and a mean of 1.8 trillion cubic feet of undiscovered natural gas in the Eastern Great Basin Province.
The U.S. Geological Survey (USGS) recently completed an assessment of the undiscovered oil and gas potential of the Eastern Great Basin Province of eastern Nevada, western Utah, southeastern Idaho, and northwestern Arizona (fig. 1). The province includes Neogene basins, Neogene ranges and structures, the central Nevada thrust belt, and the Sevier thrust belt. The assessment was based on the primary geologic elements that constitute a total petroleum system (TPS): petroleum source rocks (source rock maturation, petroleum generation, and migration), reservoir rocks (based on sequence stratigraphy and petrophysical properties), and petroleum traps (formation and timing). Using this geologic framework, the USGS defined the Paleozoic-Tertiary Composite TPS and three assessment units (AU) within the TPS, and quantitatively estimated the undiscovered oil and gas resources within the three AUs (table 1).
Figure 1. The Eastern Great Basin Province (red line) of Nevada, Utah, Idaho, and Arizona. Shown are major thrust faults, teeth on upthrown side.
The USGS estimated a mean of 1.6 billion barrels of oil (BBO), a mean of 1.8 trillion cubic feet of gas (TCFG), and a mean of 85 million barrels of total natural gas liquids (MMBNGL) in the Paleozoic-Tertiary Composite TPS. All of the assessed undiscovered oil and gas resources are conventional (table 1).
Of the total mean 1.6 billion barrels of oil (BBO), a mean of 827 million barrels of oil (MMBO) is estimated to be in the Neogene Basins AU, a mean of 470 MMBO in the Ranges and Other Structures AU, and a mean of 301 MMBO in the Sevier Thrust System AU.
Of the 1.8 TCFG, about 0.1 TCFG is estimated to be in the Neogene Basins AU, 1.2 TCFG in the Ranges and Other Structures AU, and 0.5 TCFG in the Sevier Thrust System AU.
Table 1. Eastern Great Basin Province assessment results. [MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. For gas fields, all liquids are included under the NGL (natural gas liquids) category. F95 represents a 95-percent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles are additive under the assumption of perfect positive correlation. Gray shade indicates not applicable]
The range in estimates of undiscovered conventional oil and gas (table 1) reﬂects the uncertainty of assessing new ﬁeld discoveries in the Eastern Great Basin Province. The small number of drilled wells and producing wells compared to the total geographic area of the province indicates a frontier (or unproven) status. The Neogene Basins AU has the best potential to add new reserves, with current production serving as a successful analogue. The Ranges and Other Structures AU is hypothetical with no current production. The recently discovered Covenant ﬁeld in the Sevier Thrust System AU provides insight into the potential of that area.
Oil shale, coal-bed gas, and biogenic gas were not quantitatively assessed in this study.
Supporting geologic studies of total petroleum systems and assessment units and the methodology used in the Eastern Great Basin Province are in progress. Assessment results are available at the USGS Central Energy Team Web site: http://energy.cr.usgs.gov/oilgas/noga/index.htm
Eastern Great Basin Assessment Team
Lawrence O. Anna (firstname.lastname@example.org, 303.236.5451), Laura N.R. Roberts, Christopher J. Potter, Ronald R. Charpentier, Troy Cook, Timothy R. Klett, Richard M. Pollastro, and Christopher J. Schenk.
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