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Sierra Geothermal discovered temperatures hot enough for large-scale geothermal energy production at one of its wells near Silver Peak, Nev. | Photo courtesy of Sierra Geothermal
In May 2010, Sierra Geothermal determined temperature at the bottom of a well drilled at the company's Alum project near Silver Peak, Nev., was hot enough for commercial-sized geothermal energy production - measured as 147 degrees Celsius (297 degrees Fahrenheit). "It shows we have reached commercial temperatures," says Joel Ronne, Sierra Geothermal's chief operating officer and vice president. A promising discovery by a geothermal energy company could boost use of the renewable source in southwest Nevada, power thousands of homes and create jobs.
During the drilling process of the 4,868-foot well, Sierra Geothermal also found permeable rock, an essential ingredient for large scale energy production. Sierra Geothermal seeks to have a 30-megawatt plant online at Alum by 2014, which could power about 20,000 homes per year.
The U.S. Department of Energy's Geothermal Technologies Program awarded Sierra Geothermal $5 million through the American Recovery and Reinvestment Act to help fund the $12 million project, which seeks to confirm the potential for geothermal energy at Alum and demonstrate new exploration techniques.
Coils and 3D technology
Since the project began at Alum in November 2009, two wells have been drilled and several innovative technologies have been used to locate and drill for potential geothermal resources.
Sierra Geothermal’s Alum project is partially funded through the U.S. Department of Energy’s Geothermal Technologies Program (GTP). The company was awarded $5 million in Recovery Act funds for GTP’s Validation of Innovative Exploration Technologies program. Alum is one of several projects funded by GTP under its mission to research, develop, and demonstrate geothermal technologies. For a searchable database of GTP projects, click here.
These technologies solve a major problem often encountered in traditional rotary drilling for geothermal exploration. Since the drill string used to bore through rock consists of 30 foot joints or segments of pipe, deep drilling requires the process to be frequently interrupted as more joints or segments are added. This method can cause huge delays in production.
"The objective is to keep the bit turning on the bottom of the hole minimizing the non productive time, every time you drill another 30 feet you have to stop and put another joint of pipe in which slows everything down and can lead to complications like lost circulation and can even get you stuck in the hole," Ronne says.
The new technique called coiled tube drilling, which Sierra Geothermal used on the well, can drill continuously.
Instead of drill pipe, coiled tubing drill rigs use a continuous steel tube that is rolled onto a reel. Since the tubing is flexible and contains no joints, the drill can run continuously, making the technique more efficient. "With a coiled tubing drill rig you can drill a whole section of a well without stopping, whereas before to drill the same section you might have to stop 100 times or more" says Ronne.
To find possible geothermal sites, the company deployed a technology often used to help mineralogists find new mineral deposits - hyperspectral imaging. Aerial photography used to scan Alum with hypserspectral sensors provided an "indication of where different geothermal indicator minerals are located," Ronne explains.
Hyperspectral sensors detect portions of the electromagnetic spectrum and collect data as images of different bands or frequencies, which illustrate minerals using colors. The pictures are analyzed to identify minerals that are associated with geothermal activity. "Different minerals reflect different frequencies in varying amounts, giving them unique signatures so various minerals will show up as different colors," says Ronne. "It's similar to taking an image of just the blue light and another of just the red."
Exploring geothermal resources
The company has also developed a 3-D model of Alum's subsurface using geophysical information such as the magnetic and gravity data acquired at the surface. The tool provides Sierra Geothermal with a geological model for what is happening below the surface. The 3-D model will be merged with temperature data to help Sierra Geothermal prioritize where to drill.
So far, about 30 workers have been hired for phase one of the Alum project; Sierra Geothermal expects to create 12 to 14 permanent full-time jobs if the power plant is built.
The plant will be the southern-most large scale geothermal energy source in Nevada and will bring much needed economic relief to Esmeralda County, an area battered by the recession. "It could have a huge impact on the county's economy," says Ronne.
Sierra Geothermal has announced it is joining forces with Ram Power, which controls the lease adjacent to the Alum property. The deal is expected to be finalized in August for the combined entity to move forward with geothermal exploration plans.