AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA
Although large tracts in northeastern Nevada contain one, two, or perhaps even three parameters of the Critical Quartet, only narrow fairways show the overlap of mature source, reservoir, migration, and trap. These fairways have been delineated during the course of this evaluation and are offered as a tool with which the ambitious explorationist can discover petroleum in northeastern Nevada.
The data and results of the evaluation have been divided into volumes which address the stratigraphy, structure, geochemistry and geo-thermometry, prospects and conclusions and reference materials used.
The stratigraphy includes systematic descriptions of tectono-stratigraphic assemblages, the stratigraphic groups, formations and units, and their depositional setting. Stratigraphic units have been described systematically using a format which includes the type-section, geologic age, general lithology, average thickness, areal distribution, depositional setting, and where appropriate, a discussion of the exploration significance of the unit. The concluding portion of the second Stratigraphy Volume is a brief and concise paleogeography which summarizes the depositional framework in a chronological manner. The reader is encouraged to read the paleogeography section both before and after reading the rest of the stratigraphy.
The Structure Volume is divided into three major sections. The first section details the regional structural setting, and includes an examination of the major structural events/elements responsible for the creation of the present structural architecture of northeastern Nevada. The second portion is a description of the regional structural style focusing on the geometry of the ranges and valleys present within the evaluation area. The third portion of this volume is a discussion of the major structural domains with exploration significance, and a detailing of several potential hydrocarbon trap types within the evaluation area.
The Geochemical and Geothermal Data Volume presents the data and discusses the results of the 287 surface geochemical samples collected from 12 formations by Western Cordillera geologists. The gas chromatographic analysis of the Blackburn, Grant Canyon, Trap Spring and Eagle Springs oils and possible source equivalents are also discussed in the geochemical portion of this volume. The geothermal analysis includes the written and graphical interpretation of bottomhole temperature data compiled from 214 wells in the evaluation area. This data shows the distribution of modern geothermal gradients across the evaluation area. The final segment of the geothermal portion of the volume is the data and results of 13 samples analyzed for microcline paleothermometry. These analyses show the distribution of past thermal events capable of hydrocarbon generation.
The final volume is a discussion of the results and conclusions of the entire evaluation. Specific hydrocarbon prospects delineated by Western Cordillera are presented and discussed. We feel these prospects have high potential for undiscovered hydrocarbon accumulations within the evaluation area. The references used during the course of this evaluation are also included in the final volume.
Several plates and overlay displays have also been created for this evaluation. A detailed state of the art 1:200,000 Geologic Map of Northeastern Nevada (Plate I) was compiled from U.S.G.S., thesis and Western Cordillera mapping. An overlay showing the Sources of Geologic Map Data used for compilation is included as Overlay I.
With the exception of a time datumed Stratigraphic Correlation Diagram of Northeast Nevada, Plate II, the remaining displays were built to overlay the base map, and can therefore be stacked and compared with the surface geology. The correlation diagram incorporates 32 stratigraphic sections showing the regional correlation of units discussed in the stratigraphy volume.
A Cenozoic Basin Fill Isopach Overlay II, was carefully constructed by examining the available well logs and bouguer gravity data. This isopach provides a description of the depth and architecture of the Tertiary-formed basins in the evaluation area.
A Structural Domains Overlay III, details domains with consistent structural style. This overlay provides a visual characterization of structurally complicated and variable areas discussed in the structure volume. Major basin-bounding high-angle normal faults, lateral faults and lineaments are also presented on this overlay.
The organic carbon and maturity data have been contoured on individual TOC and TAI - Vitrinite Reflectance overlays for the Elko Formation and Triassic Sediments (Overlays V, and VI), the Chainman, Diamond Peak, Webb and Eleana Formations (Overlays VII and VIII), the Pilot, Woodruff and Roberts Mountains Formations (Overlays IX and X), and the Vinini and Valmy Formations (Overlays XI and XII). These overlays show the regional distribution of organic lean and rich rocks which are immature, mature, or overmature with respect to hydrocarbon generation. Radiometric age determinations on extrusive, intrusive and metamorphic rocks were compiled and displayed on the Radiometric Age Data Overlay XIII. The radiometric date and error bar, as well as the rock or mineral dated are specified. This overlay is instructive in understanding the timing of regional and local structural and thermal events.
The modern thermal gradients and fairways determined from the bottomhole thermal analysis are plotted and contoured on the Bottomhole Thermal Gradient Overlay XIV. This overlay utilizes the bottomhole temperature data obtained from 214 wells.
The results of the microcline paleothermometry discussed in the geochemistry and geothermal volume are shown graphically on the Microcline Paleothermometry Overlay XV. The release spectra plots, and isochron or mean ages for hydrocarbon generation events are presented. They show a regional distribution and age of particular thermal events that have affected the stratigraphic section.
The mature source fairways and hydrocarbon prospects delineated during this evaluation are composited on Prospects Overlay XVI. This overlay is a composite of the geochemical and structure overlays and shows areas with discrete closures.
We encourage the reader to take the time necessary to read all of the volumes and examine all of the plates and overlays included in this evaluation. It is our hope that this evaluation will stimulate discussion and lead to positive action culminating in the drilling of viable prospects.