Test site for geopressured geothermal well-Frio sandstone, Texas Gulf coast.




Bebout, D.G.; Loucks, R.G.; Gregory, A.R.

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University of Texas at Austin, Bureau of Economic Geology


A geopressured geothermal reservoir should have a sand volume of 3 cu mi (4.8 cu km) - 50 sq mi (130 sq km) in area and 300 ft (90 m) thick-subsurface fluid temperature of 300 F (150C), and permeability of at least 20 md. Data available suggest that the water will be saturated with methane. Regional and detailed studies of the Frio Formation along the Texas Gulf Coast have been completed by the Bureau of Economic Geology to develop such a prospect. In Hidalgo, Kenedy, Nueces, Matagorda, Brazoria, and Galveston Counties, several large fairways have been identified which have sufficient san thickness and fluid temperatures to be prospective. However, optimum permeability in sand bodies deeper than 12,000 feet (3600 m) is present in the quarts-rich sands of the Brazoria-Galveston County Fairway. For this reason, more detailed work has centered on this area and the Austin Bayou prospect has been identified. The Austin Bayou prospect has maximum dimensions of 10 by 25 mi (16 by 40 km) but, because of faulting, individual reservoirs willb e less than 60 sq mi (90 sq km) in area. The 10 to 30 ft (3 to 10 km) think samds cumulate to 1,200 ft (360 km) and permeabilities of 100 md are common. Sub-surface fluid temperatures are as high as 320 degrees F (160 degrees C). The reservoir sand in the austin Bayou propect is in the Anomalina bilateralis zone of the lower Frio where an early sand depocenter prograded caused it to be buried deeper and high subsurface fluid temperatures resulted. The Austin Bayou prospect meets all of the geological requirements for a geopressured geothermal reservoir. Barring environmental and legal problems, it is anticipated that a test well will be drilled in this area to evaluate further this potential alternate source of energy.




geology; sedimentation; sediments; sandstone; Frio sandstone; geological structures; legal aspects; geothermal power; energy resources