Geothermal energy development has a promising future as part of a broad energy supply mix to meet growing demand in the United States and globally. Currently developed hydrothermal systems are a significant energy source, but these systems have limited geographic extent. Research is underway, including ongoing pilot projects, to evaluate the potential for EGS, or Engineered Geothermal Systems, to drill into hot crystalline rock and create fractured reservoirs suitable for water injection and production cycles. However, a challenge to the economics of these systems is the drilling and fracturing cost.
" Co-production" of geothermal energy associated with oil operations has been demonstrated successfully at Teapot Dome (Anderson et al, 2009), where produced water is of sufficient quantity and adequate temperature to generate electricity with binary/hybrid systems. However, this approach has yet to be embraced by the oil industry.
A potential new path toward expanded geothermal energy production is to use known porous and permeable reservoir rocks in appropriate sedimentary basins, where those packages of rocks have sufficient temperature, thickness, porosity, and permeability, existing at depths that are not so great that drilling costs make the potential system uneconomic. This presentation describes a DOE-funded project to identify, screen, and model these potential systems, incorporating geology, engineering, and economic modeling disciplines.
Although sediment-hosted geothermal systems have not previously been an exploration target in the U.S., some producing reservoirs are hosted in sedimentary units. Many of the Imperial Valley geothermal systems (for example Salton Sea, Heber, and Cerro Prieto) are hosted in Quaternary-Tertiary sediments that have accumulated in the rift-basins associated with plate boundaries. A few Basin and Range geothermal systems are also hosted in Paleozoic and older sedimentary units (for example Cove Fort and Thermo, Utah). But a much larger potential target exists in " deep" sedimentary basins with known reservoir rocks, especially many that have produced oil and gas and that have extensive datasets available.