Basin-Centered Stratigraphic Reservoirs – Potential for Large Scale Geothermal Power Generation in the U.S.

Abstract

Recent growth in the installed geothermal power capacity of the U.S. has utilized binary plants mostly located on moderate-temperature hydrothermal systems. Many of the more attractive and accessible systems have been developed or are under investigation, and blind hydrothermal systems are difficult to locate. These moderate temperature systems are typically small (< 10 km2 in area) and power plants are often 10 – 30 MWe in size. If the U.S. is to achieve 5 - 10 GWe growth in geothermal capacity during the next decade as advocated by the Dept. of Energy Geothermal Technologies Office, it requires 100 MWe-scale power developments. This size power plant requires reservoir volumes of ~ 10 km3 for developments producing at near the installed capacity for at least 30 years. The modest success of EGS pilot projects since 1980, and the small size of moderate-temperature hydrothermal reservoirs in the western U.S. suggest limited potential for power growth in the next decade from these types of reservoirs. Stratigraphic reservoirs in high heat flow basins of the western U.S. have the potential to sustain 100 MWe-scale power developments and contribute the required growth. These sub-horizontal reservoirs need to have a temperature of at least 175°C for a levelized cost of electricity of US$ 100/MWe-hour, and are likely to be at 3 – 4 km depth in basins where the heat flow is at least 80 mW/m2. A review of porosity and permeability data from both oil reservoirs and groundwater aquifers suggests the high permeabilities required for geothermal production wells (100 mDarcy) are not uncommon. Modeling with reservoir transmissivities of 3 – 10 Darcy-meters yields power densities in the range 3 – 10 MWe/km2 of reservoir area. In the eastern Great Basin, large areas of Paleozoic carbonates underlie Tertiary– Quaternary fill in