|
Alaska’s geothermal energy resources
With many hot springs and volcanoes, Alaska has potential to make some use of natural sources for heat and power generation Alan Bailey for Petroleum News
In recognition of the potential to make use of natural geothermal energy in Alaska, the state Legislature is considering Senate Bill 161, which would enable the Alaska Department of Natural Resources to issue licenses for geothermal exploration. The licensing arrangements would be similar to those for oil and gas exploration licenses in areas of the state where oil and gas lease sales are not conducted. A geothermal facility involves the use of natural subsurface heat for power generation or other purposes.
DNR has in the past issued leases for geothermal exploration on the southern flank of the Mount Spurr volcano and on Augustine Island, both on the north side of Cook Inlet. But no geothermal development resulted from these leases.
During a meeting of the Senate Resources Committee on Feb. 21 Steve Masterman, director of Alaska’s Division of Geological and Geophysical Surveys, gave an overview of Alaska geothermal resources, as background to discussions on the proposed geothermal legislation.
Multiple factors Masterman commented that the potential to use geothermal energy as a viable heat source, to create steam or generate electricity, depends on a number of factors. There needs to be an elevated geothermal gradient in a geologic setting that allows the migration of fluids through subsurface rocks, he said. The thermal system needs to be large enough to support the desired operations. The location of the system is critical both in terms of the development costs for a geothermal facility, and in terms of viable access to an appropriately sized population or a commercial operation that can use the geothermal energy. Proximity to a power transmission system may also be important.
There are wide variations in subsurface heat flow rates around the state, with known hot springs and potential geothermal resources in a number of places. Particularly critical is the temperature of the geothermal water: The higher the water temperature, the more power can be generated. Chena hot springs in the Interior, for example, supports local power generation. The surface temperature is 60 C, while hot water entering boreholes for power production is at 80 C. The result is generation at a scale of hundreds of kilowatts, Masterman said. On the other hand, test drilling at Makushin, at Akutan in the Aleutian Islands, has revealed a temperature of nearly 200 C at a depth of a few hundred meters - this could support tens of megawatts of electricity generation, Masterman said.
However, other aspects of the geothermal resource quality are also extremely important. For example, the presence of reservoir rock with good permeability and porosity supports the flow of geothermal water, thus enabling the flow of water to a geothermal well and the replenishment of hot water in the subsurface. And the shallower the resource, the less expensive it will be to develop.
Alaska geothermal systems In general, there are two distinct types of geothermal system in Alaska: systems associated with the cooling of subsurface granite bodies, and systems associated with volcanoes along the Alaska Peninsula and the Aleutian Islands. The volcanic systems tend to be hotter, with magma near the surface capable of generating larger volumes of hot water. And, while the sometimes relatively porous and permeable volcanic rocks can form particularly effective geothermal reservoirs, in the granites the water tends to flow in fractures that need to be intersected by geothermal bore holes, Masterman said.
One distinctive fairway of granite-associated warm and hot springs runs east from the Seward Peninsula across the Alaska Interior. This region includes the well known hot springs at Chena, Circle and Manley, in the Fairbanks region. Geothermal power generation at the Chena resort has a 400-kilowatt capacity and has reduced the cost of local electricity from 30 cents to 5 cents per kilowatt hour, Masterman said. There is the potential to generate considerably more power by accessing geothermal water at higher temperatures at depth, he said.
Masterman commented that the most interesting hot spring on the Seward Peninsula is the Pilgrim hot spring, to the north of Nome. This spring has a temperature of 92 C at a depth of 120 meters, with a potential reservoir temperature of 150 C, and a theoretical electrical power capacity of about 4 megawatts. The source of the hot water has yet to be found, but the geothermal resource has the potential to provide power for Nome, or for a potential mine towards the village of Teller to the northwest.
There is another area of granite related hot springs in southeast Alaska, running from a zone west of Juneau southeast to the Ketchikan region. There are a number of hot springs of potential interest in this area, including two springs, the Goddard and Baranof hot springs, that are particularly well situated on either side of Sitka, Masterman said. These two springs, which are based on fractures in the rocks, have been investigated to a certain extent for power generation for Sitka, he said.
Volcanic systems In the volcanic systems along the Aleutians and the Alaska Peninsula people are investigating the potential use of the Makushin geothermal system to generate power for Dutch Harbor and for the local fish processing facilities. The potential is to build an 18 or 24 megawatt plant that could produce power for as little as 14 cents per kilowatt hour, a cost that would be competitive with current production using diesel generation, Masterman said. There is a similar geothermal system on the island of Akutan that could be used to support a fish processing system there, he added. And there are other geothermal systems at False Pass, Cold Bay and King Cove, he said.
In summary, Masterman commented that Alaska does have several locations with potential geothermal resources. These resources, where technically and economically feasible to develop, can form an excellent source of sustainable energy. And the technology for geothermal development is evolving, with new technologies and production methods allowing a wider range of geothermal systems to be developed, enabling a broader definition of viable geothermal resources.
|
