1a geothermal general-asw1
TRANSCRIPT
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SOURCE: geothermal.marin.org
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Geothermal energy is the natural heat of the Earth
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Heat flows outward from Earth's interior. The crust insulates us from Earth's interior heat. The mantle is semi-molten, the outer core is liquid and the inner core is solid.
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The deeper you go, the hotter it gets (in Fahrenheit and miles).
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The deeper you go, the hotter it gets
(in Celsius and kilometers).
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Earth's crust is broken into huge plates that move apart or push together at about the rate our fingernails grow. Convection of semi-molten rock in
the upper mantle helps drive plate tectonics.
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New crust forms along mid-ocean spreading centers and continental rift zones. When plates meet, one can slide
beneath another. Plumes of magma rise from the edges of sinking plates.
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Thinned or fractured crust allows magma to rise to the surface as lava. Most magma doesn't reach the surface
but heats large regions of underground rock.
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Rainwater can seep down faults and fractured rocks for miles. After being heated, it can return to the surface as
steam or hot water.
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When hot water and steam reach the surface, they can form fumaroles, hot springs, mud pots and other
interesting phenomena.
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When the rising hot water and steam is trapped in permeable and porous rocks under a layer of
impermeable rock, it can form a geothermal reservoir.
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Powerful Energy Source
Geothermal reservoirs can reach Geothermal reservoirs can reach
temperatures of 700temperatures of 70000F/ 370F/ 37000C C
(more than 3 minutes boiling)(more than 3 minutes boiling)
A geothermal reservoir is a powerful A geothermal reservoir is a powerful
source of energysource of energy
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Many areas have accessible geothermal resources, especially countries along the circum-Pacific "Ring of Fire," spreading
centers, continental rift zones and other hot spots.
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Exploration commonly begins with analysis of satellite images and aerial photographs
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Volcanoes are obvious indications of underground heat, this volcano, Mt. Mayon in the Albay province of the
Philippines erupted in 1999.
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Geologists explore volcanic regions to find the most likely areas for further study, like this steaming hillside
in El Hoyo, Nicaragua.
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Geologic landforms and fault structures are mapped in the region. This view overlooks Basin and Range terrain
East of the Sierra Nevadas.
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Geologic maps like this one are created, showing
rock type and ages in different colors.
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Data from electrical, magnetic, chemical and seismic
surveys is gathered in the field.
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The data obtained in the field are displayed in various
ways and analyzed
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Geologists and drillers study the data to decide whether to recommend drilling. Geothermal reservoirs suitable for commercial use can only be discovered by
drilling.
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First, a small- diameter "temperature gradient hole" is drilled (some only 200' deep, some over 4000 feet deep) with a truck-mounted rig to determine the temperatures
and underground rock types.
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Workers on a temperature gradient hole drilling project.
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Either rock fragments or long cores of rock are brought up from deep down the hole and temperatures are
measured at depth.
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Geologists examine the cored rock (shown here marked
with depth markers).
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Temperature results like this would definitely encourage the drilling of a larger, deeper well to try to find a
hydrothermal reservoir.
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Production-sized wells require large drill rigs like these and can cost as much as a million dollars or more to drill.
Geothermal wells can be drilled over two miles deep.
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On these large rigs, drilling continues 24 hours per day
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If a reservoir is discovered, characteristics of the well and
the reservoir are tested by flowing the well.
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If the well is good enough, a wellhead, with valves and control equipment, is built onto the top of the well
casing.
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This photograph shows a vertical geothermal
well test in the Nevada Desert.