Abstract

Awareness of the energy availability problems in the United States has led to increasing curiosity about and interest in geothermal energy. The U.S. Department of Energy has contracted with state agencies in several Midcontinent states to evaluate geothermal prospects in the Midcontinent region. The data being gathered will augment and update the data published by the AAPG from their geothermal survey conducted about 10 years ago. The DOE program not only includes support for accurate geothermal gradient and heat flow measurements, but also includes programs in gravity, aeromagnetics, and geochemistry.

It is obvious from the start that this program will not discover any new "Old Faithful" type of geothermal resource. However, preliminary indications are that heat pump applications for space heating may be economically viable in this decade, especially in southeastern Kansas and northeastern Oklahoma. Geothermal gradients in that region are in the 50° C/km (2.8°F/hundred feet) range in the upper 300 meters of the sedimentary section. The gradients decrease drastically below this relatively shallow depth to about 15 to 20°C/km (0.8 to 1.1° F/hundred feet). It is not yet clear whether this change in gradient is due to changes in thermal conductivity in the sediments or to hydrothermal convection.

Low-grade geothermal energy could be produced from brine that comes to the surface as a by-product of oil production. Such energy could be used for space heating or even to eventually drive oil well pumps as low-temperature-differential engines are developed. The energy that could be extracted from such brine is six times the energy required to pump it if initial temperature is 150° and final temperature is 100°F and a lift of 3,000 feet with 50 percent pump efficiency is assumed.