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Ongoing studies of the moderate-temperature hydrogeothermal resource potential of the Atlantic coastal plain use seismic reflection data to evaluate potential reservoirs. Resource evaluation is dependent upon the determination of temperature and reservoir characteristics. The temperature of a potential reservoir can be estimated accurately if heat flow and thermal conductivity of the overlying sediments are known. Heat flow was determined in 51 shallow (300 m) exploratory holes. Equilibrium geothermal gradients in these holes indicate that thermal conductivity is a function of bulk composition, and can be characterized by the relative proportions of quartz sand, clay minerals, and water.

Seismic reflection data are being correlated with thermal conductivity of cores and cuttings from drill holes by making use of the relations between seismic velocity and bulk composition, and thermal conductivity and bulk composition. Seismic lines tied into drill holes allow interpretation of thermal conductivities between holes by correlating velocities to sedimentary units with known compositions and thermal conductivities. The seismic data are also being used to estimate the distribution and size of potential hydrothermal reservoirs by interpreting compositional differences between acquifers and aquitards.

Thus, the location, size, and temperature of potential hydrothermal reservoirs are estimated from seismic data. Preliminary results suggest that water at temperatures exceeding 60°C may occur in many areas in the eastern United States. Results of a deep test at Crisfield, Maryland, are encouraging. Brackish water at a temperature of 57°C was produced from an acquifer at a depth of 1.2 km. Further testing of the transmissibility of the deep aquifers beneath the Atlantic coastal plain is necessary.

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