Just a few weeks after filing a plan for summer aerial surveys and fieldwork on the southern flanks of Mount Spurr, an active volcano on the western side of Alaska’s Cook Inlet, Reno-based Ormat Nevada has filed another plan, this time for drilling some small-diameter core holes as part of the company’s search for a viable geothermal power source for the Southcentral Alaska electricity grid.
Ormat says that it hopes to drill four holes in September using a lightweight drilling rig carried to drill sites by helicopter. Two of the sites are in the eastern part of the exploration area, with the other two sites in the central part of the area.
Geothermal exploration often includes the drilling of small diameter holes to determine subsurface temperature gradients and to determine the nature of the subsurface rocks, Ormat says. In this case the holes will be about 3.75 inches in diameter.
Summer programAccording to the company’s earlier filed exploration plan, datasets collected from airborne surveys and fieldwork done during the summer of 2010 will help identify potential drilling locations. Fieldwork includes surface gravity measurements in the exploration region, the measurement of electrical noise, geologic mapping and water sampling. Airborne surveys include the laser measurement of landforms and the measurement of electromagnetic radiation from the land surface.
The new drilling plan says that Ormat has already identified candidate drilling sites, although the company may choose different locations after assessing updated geophysical and geochemical data gathered during the summer.
Drilling crews will operate from an on-mountain camp and will travel to each drilling site by helicopter, working at higher sites to start with, before drilling at the sites at lower elevations. Each core hole should take about five days to complete so that, even after factoring in some weather delays, it should be possible to complete the four-hole program within 30 days.
However, completion of the program this year does depend on reasonable weather conditions relatively late in the exploration season.
“The late timeframe is required in order to accommodate collection and analysis of summer 2010 phase one exploration data,” Ormat says. “Ormat duly acknowledges the vagaries of weather in Alaska and is prepared to drill in inclement weather and/or move drilling activities to summer 2011.”
After drilling each hole, project personnel will take subsurface temperature readings after two days and then again after two weeks. A geologist at base camp will log the rock cores retrieved from the holes, with the cores being later flown to Anchorage for storage in a state core repository.