Once upon a time, Texas had a very successfully working geothermal power plant. Didn't know that, did you? Most people don't. In fact when a friend visited the site, he told me that you would never know that such a plant had existed....the cattle were very happy! So where was this plant, why was it built, and what happened to it?
In 1976, the USGS and AAPG published a joint map on subsurface temperatures and geothermal gradients throughout North America using data provided by various oil and gas companies. Besides the area covered by the Delaware and Val Verde Basins of West Texas, the Gulf Coast region (Texas and Louisiana) were listed as being areas of hot subsurface temperatures.
At about the same time (mid-1970's) the Department of Energy (DOE) established a geopressured-geothermal energy program as one way to help develop alternative energy resources, in view of the increasing dependence on imported fossil fuel energy. Those of us alive in the early 1970's remember long lines at gas stations and limited amounts of fuel that could be purchased. As taken directly from the document by Chacko and others (1998), the goals of this program were "to define the extent of the geopressured reservoirs, determine the technical feasibility of reservoir development including downhole, surface and disposal technologies, establish the economics of production, identify and mitigate adverse environmental impacts, identify and resolve legal and institutional barriers and determine the viability of commercial exploitation of this resource."
Extensive work was begun across the northern Gulf Coast region for this investigation. Investigations focused on the Wilcox and Frio/Vicksburg strata as to geologic integrity and reservoir capabilities. Some 16 wells were investigated for various reservoir and resource potential. The wells were classified in one of two categories, wells of opportunity or design wells. Wells of opportunity represented those wells that various oil and gas companies made available for testing. Design wells represented wells that the DOE had drilled on potentially favorable geopressured sites based upon existing geological and geophysical studies. Two of these design wells were used for long-term studies: the Gladys McCall #1 in Cameron Parish, Louisiana; and the Pleasant Bayou #2 in Brazoria County, Texas. It was the Brazoria well that was used for developing the first hybrid-cycle geothermal power plant.
The original concept as defined in the DOE document was to tap into three forms of energy within the region: the heat brought to the surface in the produced hot water (thermal energy); burning any entrained natural gas on site for electricity production (chemical energy); and using the high brine flow rates (>20,000 bbl/day) and the high well head pressure (mechanical energy) to generate electricity. Only the thermal and chemical energy was able to be captured and effectively used during the plant test, as well as capturing exhaust heat generated from the onsite burning of the natural gas.
The hybrid binary power plant was operated between September 1989 and May 1990. Wellhead production was estimated at a minimum of 20,000 bbls/day of brine with 22 scf/bbl of gas. The plant operated on only 10,000 bbl of water per day, or 292 gal/minute. Various scale and corrosion inhibitors were highly effective throughout the operating range of brine temperatures. Bottom hole temperature was given as 154oC (309oF), with a maximum brine T of 136oC (277oF). Permeability was estimated at around 160 md with a reservoir area of 36,000 acres.
The design power plant output was 905 kW. This was represented by 541 kW from the turbine, 650 kW from the gas engine, and a parasitic load of -286 kW. A capacity factor of 80.2% was reached, due to a 3-day plant outage and a 4-week turbine outage. The overall plant availability was 97.5%, on par with many other geothermal plants. During the 121 days of operation, 3,445 MWh of electricity were sold to Houston Power and Light.
While the project was described as a success in the final report (Campbell and Hattar, 1991), the project was never able to be commercialized due to the low cost of alternative resources, specifically oil and gas. Neither did there exist a Texas mandate for renewable energy production, nor were most people concerned about sufficient electricity availability. Of course this was before the California and NE blackouts. Overall, the cost for the project was in line with then existing geothermal plants in other parts of the country. Today, times have changed and serious investigations of geothermal energy in Texas need to be updated.
A temperature of 250°F is used as a baseline for a well or field to be considered for geothermal extraction to generate electricity in Texas and the Gulf Coast. This Texas map of temperatures at 250°F is used to determine where to look for wells for geothermal electrical production. The map shows how deep (on average) drilling needs to be in an area to reach that temperature. For example, in East Texas and South Texas hotter temperatures are found closer to the surface then in West Texas
References
Chacko, J.J., G. Maciasz, and B.J. Harder, 1998, Gulf coast geopressured-geothermal program summary report compilation: Volumes I, II A, II B, III, and IV: Basin Research Institute, Louisiana State University, DOE contract DE-FG07-95ID13366.
Campbell, R.G., and M.M. Hatter, 1991, Design and operation of a geopressured-geothermal hybrid cycle power plant: Final report vol. I, 180 p. and vol. II, 172; Eaton Operating Company, Inc. and United States Department of Energy, The Ben Holt Co., DOE contract DE-ACO7-85ID12578
Also see
http://www.osti.gov/bridge/product.biblio.jsp?osti_id=6700752
pangea.stanford.edu/ERE/pdf/IGAstandard/SGW/2007/erdlac.pdf
http://www1.eere.energy.gov/geothermal/gpw/profile_texas.html
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