New technologies are becoming available that produce electricity and space heat from relatively lower-temperature rocks, such as those penetrated by some of Ohio’s deep oil and gas wells. Ohio has produced hydrocarbons from deep boreholes since the 1860s, and approximately 275,000 documented wells have been drilled to depths from a few hundred feet to the recent record-setting depth of 13,500 feet in Belmont County. Beginning in the 1940s, the temperature log became one of the first downhole logs available for oil-and-gas exploration. In addition to geothermal energy potential, temperature log data has also become indispensible for understanding heat flow within Earth.
Modern temperature logs can resolve temperature changes as small as 0.05°F and are valuable tools for indicating shale content, fluid and gas flows into a wellbore, and cement tops and for calculating fluid resistivity and other parameters. Currently, the ODNR Division of Geological Survey is evaluating its large dataset of bottom-hole temperatures as well as more than 3,200 complete borehole temperature profiles. Selected bottom-hole temperature data will be corrected using best-practice procedures and the results will be used to construct more detailed temperature, gradient, and heat flow maps than are currently available for the state (Eckstein and others, 1982; Blackwell and others, 2004). The division also will make available deep- and shallow-geologic maps and other data relevant for low-temperature geothermal energy production.
In high-temperature geothermal plants, water or steam at very high temperatures (300–700°F [149–371°C]) is used to drive turbines that generate electricity. California has the most (48) installed geothermal power plants in the country, the first installed in 1960. Nevada is second with 20 installed power plants, while seven other states, primarily in the western United States, have at least one geothermal electric-generating project. In 2010, more than 180 geothermal projects in 15 states were in various stages of development. Electricity has been produced primarily from shallow high- and moderate-temperature geothermal sources; but electricity production from the upper end of the low-temperature geothermal range is now possible using binary-cycle power systems (Duffield and Sass, 2003; Manz, 2010).
In the binary power cycle, the working fluid (fluid with a very low boiling point) is selected to optimize the power output from a particular heat source, temperature, and fluid flow. The working fluid is vaporized by the heat flowing through the pre-heater and vaporizer. The vapor expands as it passes through the organic vapor turbine, which is coupled to the electrical generator. The exhaust vapor is subsequently cooled and condensed and is then recycled to the heater(s) and vaporizer.
Electricity production has been possible in conjunction with producing oil and gas wells and from coproduction associated with enhanced- and secondary-oil and gas recovery (McKenna and others, 2005). New research suggests electricity coproduction is possible with CO2 sequestration or with CO2-induced enhanced recovery projects (Pruess, 2006; Randolph and Saar, 2010). These techniques allow for space heating and electrical coproduction using injection fluids, such as brine or CO2, which are usually considered waste products in the energy production cycle. Binary-power technologies will become more important for recapturing energy from waste heat from large commercial electricity production and industrial processes. But this emerging technology may also become important in Ohio and other Appalachian and Illinois Basin states for deep, nonproducing wells; new oil and gas wells drilled in deep rocks; and in association with enhanced- and secondary-oil and gas recovery and CO2 sequestration.
Blackwell, D.D., and Richards, M.C., 2004, Geothermal map of North America: American Association of Petroleum Geologists, scale 1:6,500,000.
Eckstein, Yoram, Heimlich, R.A., Palmer, D.F., and Shannon, S.S., 1982, Geothermal investigations in Ohio and Pennsylvania: Los Alamos National Laboratory, LA-9223-HDR, 38 p.
Manz, L., 2010, Enhanced geothermal systems: North Dakota Department of Mineral Resources, Geo News, v. 37, no. 1, p. 10–12.
Pruess, K., 2006, Enhanced geothermal systems (EGS) using CO2 as working fluid—a novel approach for generating renewable energy with simultaneous sequestration of carbon: Geothermics, v. 35, no. 4, p. 351–367.