A promising opportunity
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Mount Spurr exhibits all parameters for a potential geothermal energy source
Alan Bailey for Petroleum News
Mount Spurr, an active volcano about 80 miles west of Anchorage, exhibits all three indicators of a potential source of geothermal energy, geothermal consultant Dr. Stephen Onacha, has told Petroleum News. Those indicators consist of a source of heat, abundant water for transporting the heat and fractures in the rocks that can provide channels for the water, Onacha said.
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The heat is associated with the volcanic activity, with the eruption history indicating that the heat is not excessively deep, another important consideration in the evaluation of the geothermal potential. There is obviously plenty of water in the region, given the high rainfall and the annual snow melt. And, with an active geologic fault system, the rocks around Mount Spurr are known to be extensively fractured.
The fault system can act as a channel both for hot water to flow from depth and for cold water to flow into the geothermal system, Onacha said.
Exploration project Onacha is working with GeoAlaska LLC on a project to explore for and potentially develop Mount Spurr geothermal resources, in conjunction with a two-year state geothermal prospecting license covering three state land tracts amounting to 6,376 acres. The land is on the south flank of the Crater Peak, the volcano’s active crater, and on land at the foot of the volcano extending south to the Chakachatna River. GeoAlaska is 100% owned by Dr. Paul Craig, an Anchorage resident with a long history of investing in the Alaska energy industry.
Analysis of the chemistry of water flowing from underground can provide insights into how the water has interacted with subsurface rocks and what temperature the water has reached, Onacha said. Based on this type of information, it appears that the geothermal water reservoir at Mount Spurr is at a temperature in excess of 260 C at a depth in excess of 2.5 kilometers (8,200 feet), he said. The actual geothermal well depth needed to support a viable geothermal project would involve a tradeoff between higher temperatures at greater depths, and the higher cost of drilling deeper wells, he said.
Onacha commented that hot springs in the area already provide evidence of water cycling through a geothermal system.
The big question is where best to drill, to tap into a viable resource.
Wells need to target fractures Given the relative impermeability of the subsurface rocks, wells would need to target fractures in the rocks that carry water, at depths where the water is at appropriate temperatures for geothermal use - the water tends to be relatively cold at shallow depths. The concept is to drill wells directionally along fractures towards Crater Peak, where temperatures are probably higher, Onacha said.
In addition to locating rock fractures through geologic research, it is possible to locate subsurface fractures through geophysical data analysis. The geophysical analysis is conducted using data from surface recordings of vibrations originating from earthquakes. In addition, the measurement of electric and magnetic signals that are transmitted naturally from the Earth can provide data that give insights into the electrical conductivity of the subsurface - relatively high conductivity can indicate the presence of subsurface water at elevated temperatures.
One of GeoAlaska’s exploration targets is the Capps Glacier Fault, a regional fault that runs approximately southwest to northeast, south of Crater Peak, Onacha said.
Surface exploration Next spring GeoAlaska plans to conduct some onsite exploration, collecting electrical conductivity data, and drilling 3,000-foot wells for measuring the subsurface temperature gradient. The company would like to construct a 3D model of the subsurface electrical signal, to help figure out where to conduct deeper drilling and to evaluate the scale of the resource. The expectation for future development is to start with a 35 megawatt power plant, with the possibility of future expansion, Onacha said.
Ormat Technologies, a Lower 48 geothermal company, conducted some Mount Spurr geothermal exploration on state leases between 2008 and 2011. The company failed to find a viable geothermal resource and eventually relinquished its leases. However, the Ormat exploration took place to the east of the area where GeoAlaska is exploring. Onacha commented that Ormat drilled in areas distant from where GeoAlaska thinks that the resource exists. Moreover, a well that drilled through a fault did not drill deep enough to encounter hot fluid. On the other hand, one of the Ormat wells did exhibit a higher temperature gradient, Onacha said.
A good location A major incentive for geothermal development at Mount Spurr arises from the fact that the location lies only about 40 miles from the gas-fired Beluga power generation facility, the nearest point on the Railbelt electricity transmission system. However, Onacha suggested that there may be additional uses for Mount Spurr geothermal, such as the use of the geothermal heat to support agriculture. In Iceland, geothermal developments have become popular as sites for recreational hot pools, he commented.
Onacha also said that GeoAlaska is figuring out how to engage with stakeholders in the system, to ensure that the project runs smoothly. He commented that the company hope to support the local community by training people to work as field technicians.
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