Wide-ranging estimates of the magnitude and economic viability of the geopressured geothermal resource along the Gulf Coast have resulted in the establishment of significant research efforts in Texas and Louisiana. The energy resource consists of the heat and pressure of water, and the dissolved methane. The amount of methane in solution is directly related to the temperature, pressure, and salinity. Major questions being addressed by this research relate to prediction of subsurface fluid salinity and reservoir deliverability (size of contiguous sandstone unit, permeability, rock compressibility).

Success of the geopressured geothermal resource development is dependent upon identifying large, geopressured sandstone reservoirs with high permeability (20 md or greater), high temperature (higher than 250°F or 121°C), and low salinity (lower than 60,000 ppm). Extensive studies in Texas and Louisiana show that areas with favorable combinations of all these parameters are difficult to find. Subsurface data indicate that thick sandstones of the main-sand depocenters are, in most areas, not geopressured. Geopressured reservoirs, for the most part, lie gulfward within growth-faulted, delta-front sequences consisting of thick shales and thinner sandstones. Most wells which penetrate this delta-front section show that fluid temperature and pressure increase, and salinity decreas s, with depth; sandstone reservoir thickness and permeability decrease with depth. Therefore, the ideal geopressured geothermal reservoir is an exception and a compromise must be made.

Despite the limitations of locating an ideal reservoir, several short-term deep tests by industry have provided encouragement. More extensive long-term testing, now underway through the U.S. Department of Energy geopressured-geothermal Designed-Well Program, is providing answers to some of the questions.

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