References

1
Overview of Gulf Coast Geopressure Settings
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(John et. al 1998)
The Texas and Louisiana Gulf Coast region of the
US holds vast reserves of potential energy. This
energy falls into the category of geopressured
water resources. As the name implies, the water
at depth is over pressured and therefore flows to
the surface under its own power. This water
carries with it two important sources of energy,
natural gas and geothermal heat. Both can be
separated from the water and processed into
usable energy allowing the water to be reinjected
back into the earth. From 1975 to 1988 the US
Department of Energy spent millions of dollars
for data compilation and reports outlining
potential geopressure prospects. These reports
include, but are not limited to, temperature at
depth, geochemistry and geologic structure. The
data come from the multitude of wells along the
Gulf Coast. The reports culminated in outlining
what are called geopressured "fairways." These
fairways are areas in which several factors
overlap. First, the underlying formations must
have large bodies of high porosity sands and
therefore large volumes of water. This water has
to be overpressured thereby giving it a greater
thermal gradient. This provides higher
temperature water at a shallower depth. These
areas of overlapping characteristics, or
"fairways", are places where favorable conditions
exist for geothermal energy to be produced.
DOE Test wells From the mid 1970s to the early
1990s the DOE sponsored geopressure research on
wells in the Gulf Coast. Sixteen wells were
chosen and divided into two programs, Wells of
Opportunity and Design Wells. The Wells of
Opportunity focused on wells provided by the oil
and gas industry where geopressured reservoirs
were penetrated. Design wells were placed where
geologic and geophysical data indicated best
conditions for a geopressure prospect. Data
gathered include subsurface structure, regional
sandstone distribution, porosity permeability,
temperature, formation pressure and salinity.
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Temperature at Depth These temperature models
were calculated quantitatively using the
following relation where T(x) is the
temperature at depth x, Q0 is the surface heat
flow, K is the average thermal conductivity from
the surface to depth x, and A0 is the radioactive
heat contribution from crustal rocks. Target
temperatures (in pink) in the geopressured
fairways are reached as shallow as 4 km.
Pleasant Bayou Power Plant DOE with the Ben Holt
Company began operating the Pleasant Bayou Power
Plant, located in Brazoria, Texas, in 1989. The 1
MW plant produced 39.2 MMscf of methane gas and
1.4 MMstb of hot brine to produced 3,445 MWh of
electricity running at 98 capacity during its
operational run from November 1989 to May 1990.
Brazoria Fairway
200F
Top of geopressure
300F
Reservoir
Salt withdrawal basin
Corpus Christi Matagorda Fairways
Frio Sands These two figures show reservoirs
located in the Frio sandstone formation. The red
dashed lines are 200 and 300F isotherms, while
the blue lines represent the top of the
geopressure. This figure as well as the report
itself outlines in detail each of the fairways
positive and negative aspects. In the past, the
cutoff temperature has been the 300F isotherm,
todays standard of 230F is lower and
encompasses larger volume.
200F

• Brazoria Fairway
• thick sand
• high temperature
• high permeability

300F
Top of geopressure
References Bebout, D.G., Loucks, R.G., Gregory,
A.R., Report of Investigations No. 91 Frio
Sandstone Reservoirs in the Deep Subsurface Along
the Texas Gulf Coast Their Potential for
Production of Geopressured Geothermal Energy.
Bureau of Economic Geology, University of Texas
at Austin, Austin Texas, 1978. Bebout, D.G.,
Weise, B.R., Gregory, A.R., Edwards, M.B., Wilcox
Sandstone Reservoirs in the Deep Subsurface Along
the Texas Gulf Coast Their Potential for the
Production of Geothermal Energy, Bureau of
Economic Geology, University of Texas at Austin,
Austin, Texas, 1982. Blackwell, D.D., Negraru,
P.T., and Richards, M.C., Assessment of the
Enhanced Geothermal System Resource Base of the
United States, Natural Resources Research, DOI
10.1007/s11053-007-9028-7, 2007. Campbell, R.
G., and Hattar, M. M., Operating results from a
hybrid cycle power plant on a geopressured well,
Geothermal Resources Council Trans., 14, 521-530,
1990. Campbell, Richard G. Hatter, Mai M..
Design and Operation of a Geopressured-Geothermal
Hybrid Cycle Power Plant Final Volume I
February 1991. The Ben Holt Co. Pasadena,
California, 1991. Campbell, R.G., Hatter, M.M.,
Design and Operation of a Geopressured-Geothermal
Hybrid Cycle Power Plant Final Report Volume
II February 1991. The Ben Holt Co. Pasadena,
California, 1991. John, C.J., Maciasz, G.,
Harder, B.J., Gulf Coast Geopressured
Geothermal Program Summary Report Compilation
Volume I Executive Summary. Basin Research
Institute, Louisiana State University. Baton
Rouge, Louisiana, 1998.
Reservoir

• Matagorda Fairway
• thin sand
• limited aerial distribution
• high temperature
• high permeability

Hidalgo Armstrong Fairways
200F

• Corpus Christi
• thin sand
• high temperature
• low permeability

Top of geopressure
300F
Reservoir

• Armstrong Fairway
• thick sand
• moderate temperature
• permeability unknown

Poster by Patrick R. Stepp Southern Methodist
University

• Hidalgo Fairway
• thick sand
• high temperature
• low permeability

0 25 50 miles
(Bebout et. al 1978)