Major Oil Plays in Utah and Vicinity
By Thomas C. Chidsey, Jr
One of the benefits of Utah’s diverse geology is a wealth of petroleum resources. Three oil-producing provinces exist in Utah and adjacent parts of Wyoming, Colorado, and Arizona—the thrust belt, Paradox Basin, and Uinta Basin. Utah produces oil from eight major “plays” within these provinces, where a play is defined by the U.S. Geological Survey as a set of known or postulated oil accumulations sharing similar geologic, geographic, and temporal properties such as hydrocarbon-generating source rocks, oil migration pathways, trapping mechanisms, and hydrocarbon types. The Utah Geological Survey (UGS) has recently completed a study, funded in part by the U.S. Department of Energy, that describes concisely and in new detail each of these major oil plays.
Utah Oil Production and Proven Reserves
Utah oil fields have produced over 1.36 billion barrels since production began in the 1940s. Although production declined from the mid1980s to 2002, when it reached a 40-year low, the trend has since reversed. Discovery of Covenant oil field in the central Utah thrust belt (“Hingeline”) play and increased development drilling in the Uinta Basin have stimulated the increased production. Among oil-producing states, Utah currently ranks eleventh in domestic oil production. There are over 200 active oil fields in Utah.
Despite over 40 years of production at rates that have varied by a factor of three, Utah’s proven oil reserves during this time have remained above 200 million barrels, indicating significant oil remains to be produced. As of 2009, proven reserves are relatively high, at 355 million barrels. With higher oil prices now prevailing, state-of-the-art horizontal drilling and secondary and tertiary recovery techniques should boost future production rates and ultimate recovery from known fields.
Potential Increased Recovery/New Technology
While Utah still contains large areas that are virtually unexplored, there is also significant potential for increased recovery from existing fields by improved understanding of reservoir (the oil-producing rock layers) characteristics and use of the latest drilling, wellcompletion, and secondary/tertiary production technologies. New exploratory targets may be identified and better defined using advanced technologies such as three-dimensional (3-D) seismic surveys or soil-gas surveys. Development of potential prospects is within the economic and technical capabilities of both major and small independent companies.
New UGS Study
The new UGS study will help increase recoverable oil reserves from existing field reservoirs and new discoveries by providing play portfolios for the major oil-producing provinces. The play portfolios include the following descriptions: (1) tectonic setting, (2) reservoir stratigraphy, thickness, and rock types (lithology), (3) type of oil traps, (4) rock properties, (5) oil and gas chemical and physical characteristics, (6) source rocks including timing of generation and migration of oil, (7) exploration and production history, (8) case-study oil field evaluations, (9) summaries of the state-of-the-art current and potential best drilling, completion, and production practices, and potential for new secondary/tertiary enhanced oil recovery, (10) descriptions of reservoir outcrop analogs for each play, (11) exploration potential and trends, and (12) maps of the major oil plays and subplays.
• The 2004 discovery of the 100-million-barrel Covenant field in the central Utah thrust belt changed the oil development potential of the Jurassic (176 million years) Navajo Sandstone Hingeline play from hypothetical to proven (another field, Providence, was discovered in 2008). Deep, Paleozoic-cored thrust structures (folds developed along low-angle faults where older rocks have been pushed over younger rocks) represent numerous future drilling targets.
• The best reservoir properties associated with the Mississippian (340 million years) Leadville Limestone Paradox Basin play were developed during late (34 million years), deep subsurface hydrothermal activity. Relatively low-cost surface geochemical surveys, hydrodynamic analysis, and other innovative techniques can identify potential Leadville hydrocarbon migration patterns and oil-prone areas in this environmentally sensitive region.
• Mapping the environments in which the reservoir rocks were deposited in the Paradox Formation (Pennsylvanian age—308 million years) play delineated very prospective trends in the Paradox Basin that may contain untested, ancient reef-like and Bahamas bank types of carbonate buildups that are potential hydrocarbon traps.
• In the Uinta Basin, the current production practices in several oil plays will leave a significant amount of oil unproduced in older wells. Special cased-hole well logs can identify by-passed oil in individual beds (40 or more in many wells). These beds can then be selectively stimulated to recover additional oil.
• Utah has numerous production-scale outcrop analogs that provide an excellent view of reservoir properties, environment of deposition, and lateral and vertical changes in these characteristics for each oil play. They can be used as a “template” for evaluation of data from rock core taken from wells, geophysical well logs, and seismic surveys, and the development of reservoir models for field development.
Who Benefits from the Study?
The Utah play portfolios in this study provide a comprehensive geologic, engineering, and geographic reference to help petroleum companies plan exploration, land-acquisition strategies, and field development. These portfolios can also help pipeline companies plan future facilities and pipelines. Other potential users of the portfolios include petroleum engineers, petroleum land specialists, landowners, bankers and investors, economists, utility companies, manufacturers, county planners, and numerous government resource management agencies.
Survey Notes, v. 42 no. 1, January 2010