Can Geothermal Power Replace Fossil Fuels?
Abstract
Development of geothermal energy in any capacity is a positive step toward a sustainable energy future. The resource is enormous and has the capacity to supply most future demand for electrical power if technology can meet some substantial challenges. Electrical power from geothermal energy has several compelling characteristics: a small footprint, low emissions, continuous availability, and sustainability. However, a common perception of geothermal energy is that it is available only in a few isolated localities and thus cannot contribute significantly to future electrical power needs. This perception neglects the stored thermal energy available everywhere in the upper 10 km of Earth’s crust. We are investigating the potential for power production in oil-producing sedimentary basins where subsurface temperatures are sufficient for intermediate geothermal resources (90 °C -150 °C) at depths greater than 3 km. Existing estimates of geothermal energy stored at depth in sedimentary formations in the U.S. have been based only on a few aquifers and have not included the greater volume of fluids in oil-bearing formations. We reevaluated the accessible geothermal resource base for the north central US and found that including geothermal fluids in oil-producing formations increased the resource estimate by a factor of eight. Preliminary analysis of other basins indicates that the current estimate of thermal energy in the U.S. (100,000 EJ) may be of the order of 400,000 EJ. This is particularly significant due to recent technological advances leading to commercialization of scalable organic Rankine cycle (ORC) engines. Until recently, ORC systems were available only on an at large scale, i.e., 10s of MW, and had efficiencies of about 10 percent. Currently there are at least five manufacturers making scalable ORC systems in the 50 kW to 1 MW range, and at least one system has an efficiency of about 17 percent and is expected to attain an efficiency in the low 20s as it is scaled up to produce power in the MW range. Values needed for these systems are temperatures of 92+ °C and flow rates of 140-1000 gpm. In a detailed analysis of the North Dakota part of the Williston Basin, we used heat flow, bottom-hole temperatures, and measured temperature gradients to calculate the energy contained within specific formations having temperatures in the range of 100 °C to 150 °C. We find that at a 2% recovery factor, approximately 4500 MW/hr can be recovered at depths of 3-4 km. North Dakota currently produces approximately 3100 MW/hr from non-renewable sources such as coal and petroleum. We conclude that the geothermal resource in the Williston Basin could completely replace fossil fuels as an electrical power supply for North Dakota.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.H53F1004K
- Keywords:
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- 1800 HYDROLOGY;
- 1829 HYDROLOGY / Groundwater hydrology;
- 1835 HYDROLOGY / Hydrogeophysics;
- 1878 HYDROLOGY / Water/energy interactions