ABSTRACT

Drilling of the first well designed to test the geopressured geothermal resource for a sustained period of time was initiated in July 1978. Regional and site-specific geological and engineering studies supportive of this site were conducted by the University of Texas Bureau of Economic Geology and Department of Petroleum Engineering/Center for Energy Studies with funds from the U.S. Department of Energy. The area sought during these studies had to have reservoir volume of 3 cubic miles, minimum permeability of 20 md, and fluid temperature of 300°F. The Brazoria Fairway, Brazoria and Galveston Counties, best met with these specifications and the Austin Bayou Geothermal Prospect was developed in this fairway. Funds for drilling the No. 1 and No. 2 Pleasant Bayou geothermal test wells in the Austin Bayou Prospect were provided by DOE and the operator of the wells is General Crude Oil Company.

The geopressured sandstone reservoirs occur in the lower part of the Frio Formation between the depths of 14,000 and 17,000 ft. The sandstone units occur at the top of at least seven progradational deltaic cycles; cumulative thickness of all permeable sandstone units is 250 to 300 ft. Each deltaic cycle is composed of a gradational vertical succession characterized by low-permeability prodelta and distal delta-front sandstone and shale at the base grading to permeable distributary-mouth-bar and delta-plain sandstone and shale at the top.

Fluid will be produced from the No. 2 Pleasant Bayou well, stripped of methane and heat, then injected into Miocene sandstones at 6000 to 7000 ft depth in the nearby No. 1 Pleasant Bayou disposal well. The produced water is expected to have salinities ranging from 50,000 to 80,000 ppm, temperature from 300 to 350°F, pressure from 10,000 to 15,000 psi, and 40 cubic feet of methane per barrel. The two-year test period will evaluate the feasibility of long-term production of large quantities of water (ultimately 40,000 barrels per day) from geopressured reservoirs.

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