New Developments in Oil and Gas Fields: Using Geothermal Energy for Electrical Production
Meredith L. Faber1, Maria C. Richards2, and David D. Blackwell3
1Department of Geological Sciences
P.O. Box 750395, Dallas, TX 75275-0395, 214-768-4140
2Department of Geological Sciences
P.O. Box 750395, Dallas, TX 75275-0395, 214-768-1975
3Department of Geological Sciences
P.O. Box 750395, Dallas, TX 75275-0395, 214-768-2745
Rising energy consumption in recent years has necessitated a thorough assessment of alternative energy sources, with particular emphasis on renewable resources. Geothermal energy, defined as heat produced within the Earth, has long been favored as a potential method of power generation because, unlike wind and solar resources, it is not perturbed by weather fluctuations and is a baseload power source.
Recent estimates suggest that geothermal energy is highly underutilized. According to the 2007 report on the Future of Geothermal Energy by the U.S. Department of Energy, the thermal potential available in Texas is equivalent to over 1 million Exajoules (1018 Joules) (Tester et al., 2006). Given this quantity, there is approximately 10,000 MW of electrical capacity to develop with an estimated 2,000 MW as a short-term goal. However, despite such an immense untapped natural resource, finding the appropriate locations for geothermal electrical development is problematic; fluid temperature is not a well parameter commonly recorded by the Texas Railroad Commission. Nevertheless, developing geothermally derived electrical power for commercial use is already being explored.
On January 22, 2007, 11,000 acres were leased by the Texas General Land Office to the geothermal company ORMAT Technologies for development. This sale follows upon the initial success of a geothermal-geopressure plant in Pleasant Bayou, Brazoria County, Texas which established the resource viability of geothermal-geopressure electrical production in the Gulf Coast region. Though the Pleasant Bayou test project was cut in 1990 due to extremely low oil and gas prices, today’s energy market suggests that electricity generated by geothermal power plants is cost competitive with prices between $0.05 to $0.08 per kWh.
Technological developments in both the geothermal and petroleum industries are largely responsible for the dramatic reduction in the cost of geothermally derived power. Notable among these developments is the new binary mini-power plant (225kW), a system designed to capitalize on the moderate temperature well fluids (165+ °F) present in existing oil and gas wells. Fundamentally, geothermal reservoirs are underground heat exchangers. In these binary cycle plants, well fluids circulate through a heat exchanger which transfers heat to a secondary working fluid, commonly isobutane or ammonia. The added heat converts the working fluid to gas which propels a turbine and generates electricity. Subsequent to heat extraction, the well fluids are reinjected into the geothermal reservoir via a nearby well.
These simple, modular units, which can range in power from 225kW to 1MW, require little additional infrastructure beyond that of oil and gas wells and, with proper maintenance and fluid management, have an estimated longevity of approximately 20 years and installation cost of $1-2 million. In addition, the closed-loop design renders them minimally invasive; well fluids do not contact moving parts, reducing corrosion, and emissions are carbon-free.
Existing plants, like the system in Chena, Alaska (using a temperature of 165°F), and the experimental plant in Pleasant Bayou, have successfully demonstrated the feasibility of geothermal power. The large-scale implementation of similar systems for electrical production is the focus of a current resource assessment study being conducted by the SMU Geothermal Lab.
Tester, J. W., Anderson, B., Batchelor, A., Blackwell, D., DiPippo, R., Drake, E., Garnish, J., Livesay, B., Moore, M.C., Nichols, K., Petty, S., Toksoz, N., Veatch, R., Augustine, C., Baria, R., Murphy, E., Negraru, P., Richards, M. 2006. The future of geothermal energy: Impact of enhanced geothermal systems (EGS) on the United States in the 21st century. Massachusetts Institute of Technology, DOE Contract DE-AC07-05ID14517 Final Report, 374 p.
AAPG Search and Discover Article #90065©2007 AAPG Southwest Section Meeting, Wichita Falls, Texas