This is an excerpt from EERE Network News, a weekly electronic newsletter.
Drill Problems Halt Australian Hot Dry Rock Geothermal Project
An Australian effort to build the world's first commercial geothermal plant using hot dry rock (HDR) technology has temporarily come to a halt because of drilling problems. Today's geothermal power plants tap into existing underground reservoirs consisting of hot, fractured rock permeated by water or steam. Wells tapped into these reservoirs bring the hot fluid to the surface and convert its energy into electricity. However, the geothermal power industry could be greatly expanded by tapping a much larger resource of hot underground rock that is not permeated with water, or in other words, hot dry rock. To do so requires drilling a well into the hot dry rock, fracturing the rock with hydraulic pressure by pumping water down the well, then drilling a second well to intersect the new geothermal reservoir. A power plant employing this resource would draw hot water out of one well, convert its energy into electricity, then pump the cooler water down the second well, establishing a flow of water through the underground reservoir. The HDR technology, originated at DOE's Los Alamos National Laboratory, has been hampered by the need to drill two to three miles deep through hard, high-temperature granite.
Since 2003, Geodynamics Limited has been trying to establish an HDR geothermal plant in the Cooper Basin in South Australia. Drilling of its first well, Habanero #1, went smoothly, reaching a depth of 2.75 miles in September 2003, and the reservoir was hydraulically fractured in November and December 2003. The second well, Habanero #2, successfully reached a depth of 2.6 miles by October 2004, but soon after the drill string broke, leaving a length of drill pipe in the hole. While drilling a "sidetrack"—a parallel hole to avoid the stuck drill pipe—a plug got stuck in the well. Efforts to retrieve the plug in March 2005 caused it to drop to the bottom of the well. A subsequent flow test in April 2005 found some potential for power production, but concluded that the dropped plug was restricting the connection to the geothermal reservoir. The company's attempt to drill another sidetrack had one problem after another, concluding last month when the drill pipe became stuck. The company tried to free the drill pipe, but had to sever it, leaving a quarter-mile of drill pipe in the borehole.
Geodynamics has been using "snub drilling," a technology that essentially pushes the drill string into the ground. Although this method is effective at overcoming the high pressures that exist at the bottom of the well, the company decided in late June to switch to a conventional drilling rig, which will not be available until the end of this year. At that time, Geodynamics will drill yet another sidetrack, starting at a depth of about 2.3 miles. Despite the many delays and difficulties, the company emphasizes that the drilling problems will be overcome and the project is still viable. See the project history and recent news on the Geodynamics Web site.