Discovery of a new type of
geothermal energy resource in Utah offers
hope for significantly more potential across the western U.S., and a
boost in geothermal power production.
In 2011 and 2012, Utah
Geological Survey geoscientists, in partnership with a U.S. Geological Survey research
drilling crew, drilled nine temperature gradient holes in Utah’s Black Rock Desert basin
south of Delta to test a new concept that high temperature geothermal resources
might exist beneath young sedimentary basins.
Preliminary results show that near-surface temperature gradients in the
basin vary from about 60⁰C/km (33⁰F/1000 feet) to 100⁰C/km
(55⁰F/1000
feet). This implies temperatures of 150
to 250⁰C
(300 to 500⁰F) at 3 – 4 km depth (10,000 to 13,000 feet) beneath the
basin. An abandoned oil exploration well
drilled near Pavant Butte in the central part of the basin in 1981 confirms
these exceptionally high temperatures. Seven of the drill holes were funded by the
U.S. Department of Energy as part of a National Geothermal Data System project,
managed by the Arizona Geological Survey.
The new holes also confirm the results from three other research holes that
were drilled in the basin over the past few years; these were funded by the
Utah State Energy Program and the Utah Division of Wildlife Resources.
The 1,000 square kilometer
Black Rock Desert basin is filled with unconsolidated sediments to a depth of 3
km, while the underlying basin floor comprises a variety of Paleozoic and older
bedrocks. In some parts of the basin, porous
and permeable carbonates (limestones and dolomites) are known to be present and
these would be natural hosts for a geothermal reservoir. Using the drilling results, a reservoir
modeling team at the University of Utah estimates
a basin-wide power density of about 3 to 10 MWe/km2, (megawatts of
power per square kilometer) depending on reservoir temperature and
permeability. Given the large area of
this basin, the power potential is conservatively estimated to be hundreds of
megawatts, and preliminary economic modeling suggests a cost of electricity of
about 10c per kilowatt-hour over the life of a geothermal power project. The modeling assumes air-cooled binary power
generation with all produced water injected back to the reservoir so that there
would be no emissions or consumption of water.
The heat in the produced water would be exchanged at the surface in an
air-cooled binary power plant. Such
power plants are common these days in geothermal power developments. The cool,
injected water would move laterally in the reservoir between injection and
production wells, and can be considered as heat-farming at depth.
This basin is especially
attractive for geothermal development because of the existing nearby infrastructure
─ it is next to a large coal-fired power plant, a 300 MWe wind farm, and a
major electrical transmission line to California. [Right, location
of the new temperature gradient wells in the Black Rock Desert, and the inferred temperature at 3 kilometer depth (10,000
feet; 150⁰C = 300⁰F; 200⁰C = 400⁰F). The contours of
gravity outline a basin coinciding with the region of high temperature. Credit, UGS]
Geothermal exploration in the
Basin and Range Province of
western Utah and Nevada has
traditionally focused on narrow, hydrothermal upwelling zones along bounding
faults of mountain ranges. Most current power
developments have reservoir areas of less than 5 km2 (2 square
miles). However basins within the Basin
and Range usually have areas of many hundreds of square kilometers. Although the depth to potential reservoirs
beneath these basins is deeper than the geothermal industry is used to, the
large reservoir area offers economies of scale.
Drilling to depths of 3 – 4 km is not unusual in oil and gas
developments.
Dr. Rick Allis, Director of the
Utah Geological Survey and joint lead scientist of the sedimentary basin
geothermal research project, said that existing heat flow maps of the Basin and
Range don’t have the resolution to identify this type of geothermal energy resource.
“There are other potentially hot basins across the Basin and Range province
that need to be investigated using this exploration model. We have identified the Steptoe Valley and
Mary’s River –Toano basins in northeast Nevada as
obvious geothermal targets. There may also
be hot basins across the western U.S. that
have similar unrecognized geothermal energy potential.”
The project findings are being
presented at 2:30pm on
Monday, October 1, at the annual meeting of the Geothermal Resources Council in
Reno, Nevada. A question and answer period with Dr. Allis
will take place following the close of the session at 3:45pm at the Department of
Energy Geothermal Technologies Program booth, 610-612.
The National Geothermal Data
System is in operational test mode, integrating large amounts of information
from all 50 states to enhance the nation’s ability to discover and develop
geothermal energy. Visit the State Contributions site at www.stategeothermaldata.org.
A 3
minute video with and without subtitles is available at http://geology.utah.gov/blog/.
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