Jeanne Roberts, EnergyBoom Contributor
May 28, 2010 | 3 Comments
The process for creating geothermal wells is very similar to that used for extracting oil and gas, at least in the initial phases.
A conventional drilling rig with a giant-sized drill bit rotating at variable speeds, depending on the density of the rock, drills into the earth, with water or mud circulating through the well shaft to bring rock cuttings to the surface and keep the drill bit (and the well bore) cool.
The technique changes only in the presence of high-temperature steam reservoirs. Then, the final step of drilling is accomplished with air, under pressure, to prevent drilling mud from clogging the bore and preventing the steam from emerging. The method is very nearly as old as the discovery of oil as a fuel source, and is expensive, time-consuming, dangerous and environmentally hazardous – at least in terms of fossil fuel extraction.
This method, previously used to fracture granite and marble for commercial use but effective only in surface or close-to-surface applications, is now being applied to deep-well geothermal drilling, but with water as the medium instead of air.
Not only does the method save money by not using drill bits, which break or wear out, costing crews thousands of dollars and hours of time, but drilling is continuous and considerably faster – 30 feet per hour as compared to traditional drilling’s top speed of 10 feet per hour.
The company at the forefront of this newly repurposed technology, Redwood City, California-based Potter Drilling, says that it intends to use the reinvented process to make drilling geothermal wells cheaper and more environmentally friendly. The technology can also be used, to equal advantage, in carbon sequestration, nuclear waste storage, and mining operations.
For Google, it’s part of an overall investment of more than US$30 million in renewable energy announced in 2008, $10 million of that earmarked for geothermal alone and divided among three geothermal companies/projects: AltaRock Energy, Inc., $6.25 million, including whatever was spent for its now defunct initial geothermal project at the Geysers in California; Potter Drilling, $4 million, in two payments, to develop large scale Enhanced Geothermal Systems, or EGS; and Dallas, Texas-based Southern Methodist University Geothermal Lab, $489,521, to map and evaluate U.S. geothermal energy resources.
There, in the past year and a half, the company has drilled holes ranging from one to four inches in diameter, 1,000 feet deep, to demonstrate the advantages of its hot-water spallation drilling method, which relies on the fact that rock types do not all expand the same amount when heated, resulting in stress and fracturing, the latter releasing the steam needed to power a geothermal energy system.
Geothermal energy can also be developed from hot water – either liquid already in the ground, or surface water pumped in and heated by hot rock formations – but this form of geothermal typically produces less energy because of the lower temperatures involved. (Water becomes steam because of a material phase change at 100 degrees Celsius, or 212 degrees Fahrenheit).
According to the Geothermal Energy Association, geothermal energy has the smallest land-use footprint of any power generation technology, including both traditional sources like coal and oil, and newer, renewable sources like solar and wind.
It is also more reliable than solar and wind, and can be used for baseload electricity generation; every geothermal energy plant built in the last century is still in production, even though production values may have fallen as a result of poor construction or sealing (as is also the case with the BP Gulf oil disaster), or carbonate clogging.
The single drawback to geothermal energy is the high cost of initial development, but if Potter Drilling has its way, that problem may be solved in the near future, leading to the sort of geothermal energy development that could power seven million American homes in the near term, and potentially almost the entire nation when EGS technology is perfected.
Jeanne Roberts is a freelance writer on environment and sustainability issues. In her previous life, she worked as both a reporter and a communications specialist for a major public utility. Her most recent book, Green Your Home, approaches environmentalism from a consumer’s perspective.
This article was originally published on the media outlet EnergyBoom and was reprinted with permission.
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