Significant Test Results, Energy Potential, and Geology of Some Gulf Coast Geopressured-Geothermal Sandstone Reservoirs

Chacko J. John, Donald A. Stevenson

Geopressured-geothermal reservoirs found in the northern Gulf of Mexico basin represent a large potential future energy resource. Three reservoirs in various stages of developmental testing are of current interest. Over a four-year testing period the Gladys McCall #1 (Cameron Parish, Louisiana) produced 27.3 million bbl of brine and 676 million scf of gas at an average rate of 20,000 bbl/day from perforations between 15,158 and 15,490 ft. This lower Miocene sandstone section forms part of a genetic unit of interconnected channel and point-bar sandstones deposited in a lower shelf environment. Pleasant Bayou 2 well (Brazoria County, Texas) is currently being flow-tested at 20,000 bbl/day and has a gas/brine ratio of approximately 23 scf/stb and a temperature of 291 °F An electric energy conversion system being set up here will test potential for electric generation from geopressured-geothermal energy. Superior Hulin #1 (Vermilion Parish, Louisiana) is a deep (21,549 ft) former gas well proposed to be completed as a geopressured-geothermal well. Initial log analysis indicates that a 570-ft thick sandstone, of probable submarine fan origin, may contain free gas in addition to solution gas and may thus represent an economically feasible geopressured-geothermal well. Gas-separated brine is disposed by subsurface injection into disposal wells. However, in areas where hydrocarbon fields with wells penetrating geopressured sands are present, hot brines could be injected into depleted hydrocarbon zones to aid secondary recovery.

The production and disposal of large volumes of geopressured-geothermal fluids present the potential for significant environmental problems associated with land subsidence, growth fault activation, and water quality. Hence, an environmental studies and monitoring program has been established with the aid of 13 continuous microseismic recording stations, surveyed benchmarks tied to National Geodetic Survey regional networks, and observation water wells. So far, no observable long-term detrimental effects have been noted.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.