Predicted Corrosion and Scale-Formation Properties of Geopressured Geothermal Waters From the Northern Gulf of Mexico Basin

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Abstract
Introduction: Geopressured geothermal waters arc present at depths greater than about 2500 m in Cenozoic and Mesozoic sedimentary rocks beneath an area of about 350 000 km2 in coastal Texas and Louisiana. The hydraulic pressure gradients in the geopressured zones are higher than hydrostatic [10.5 kPa/m (0.465 psi/ft)], and with increasing depth approach the psi/ft)], and with increasing depth approach the lithostatic pressure gradient of 22.6 kPa/m (1.0 psi/ft). The temperature gradients in the psi/ft). The temperature gradients in the geopressured zones also are higher than the gradients in the overlying normally pressured zone. The temperature gradient in geopressured zones in south Texas is 67 deg. C/km (3.7 deg. F/100 ft); the gradients decrease northward along coastal Texas and Louisiana (Fig. 1). There currently is an intensive research and development effort by public agencies and private companies to determine the feasibility of using these geopressured waters as sources of energy. Three forms of energy may be extracted from these waters:(1)thermal energy,(2)mechanical (hydraulic) energy, because these waters will be under high pressure at ground level, and(3)energy obtained pressure at ground level, and(3)energy obtained from dissolved gases, mainly methane, which may exceed the thermal energy if the waters are saturated with natural gas under subsurface conditions. This paper describes the chemical and physical parameters of selected geopressured geothermal parameters of selected geopressured geothermal waters that are important in determining their corrosion and scale-formation properties. The equations used here for predicting corrosion and scale formation apply to geopressured waters associated with oil and gas as well as geopressured waters from geothermal reservoirs. We have carried out detailed chemical analyses of 120 formation-water samples from geopressured and normally pressured production zones that range in depth from about 1000 to 5600 m. The 25 oil and gas fields sampled are in the McAllen-Pharr, Corpus Christi, and Houston-Galveston areas of Texas and in the Lafayette, LA, area. Oil and gas production is from sandstone reservoir rocks, which are mainly in the Frio Clay of Oligocene (?) age in Texas and of Miocene age in Louisiana. Chemical Composition: Chemical analyses of eight formation-water samples selected as typical of the geopressured zone in their respective areas appear in Table 1, which also gives the locations of the sampled wells, subsurface temperatures, pressures, and other pertinent data. More complete chemical analyses, as well as the field and laboratory procedures used for collection, preservation, and analysis, are given in Kharaka et preservation, and analysis, are given in Kharaka et al.

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