Geothermal—Drilling Hot But Ground Shaking
Geothermal—Drilling Hot But Ground Shaking
Geothermal energy, tapping into the fission heat of the Earth’s core, has the potential to supply a major part of humanity’s energy needs without major outputs of carbon dioxide. Those possibilities got both good news and bad news in mid September 2009.
The good news was provided by ETH Zurich (Switzerland) who have done the basic research for a thermal drill to penetrate rock with potential for providing geothermal energy. Drilling is typically one of the greatest costs for geothermal energy, and indeed, any place on Earth could provide geothermal energy if drilling costs were low enough.
In fact, drilling costs for geothermal tend to be high for two reasons. First, except for a rare geologic sites, deep drilling is required. Second, heat (by definition) tends to be in igneous (that is volcanic-type) rocks, or at least metamorphic (sedimentary rocks that have been cooked by nearby magma). Such rocks tend to be harder and thus slower to drill through for the conventional rotary drills developed for oil drilling.
One approach from several decades ago was an electrically heated drill head that actually melted its way through the rock. This was an energy-intensive process, and it was not particularly fast.
The ETH researchers are developing a system for providing ethanol, oxygen, and water at supercritical pressure and temperature, and then succeeding in igniting them (Science Daily, http:www.sciencedaily.com/release/2009/090912144809.htm). The resulting temperature does not melt the rock; rather, the heat difference between the flame front and the rock further back causes spalling at the flame front, and chips of rock fly off. The flow of reaction products carries the chips away. In fact, the ETH researchers want to avoid melting rock because melting results in slower drilling speeds.
Caveat: Granted, this process has been tested in an exotic high-pressure chamber; however, it has not yet been used on an actual drilling operation. Real operations could have presently unknown problems. For example, fracturing of rock might cause major drops in pressure, thus losing the high-pressure needed for the supercritical flame front. Actual demonstration projects are needed to develop working flame drills.
Meanwhile, New Scientist was one of the journals describing a worrisome side effect of geothermal power production (Sept. 16, 2009, http://www.newscientist.com/article/dn17795-geothermal-power-quakes-find-defenders.html). The New Scientist article reported that Landau in the province of Rhineland-Palatinate had suffered a 2.7 magnitude quake near its geothermal power plant. This is a facility in which a hole was drilled into hot rock and steam was injected. A Swiss facility using this method also had small earthquakes. This echoes the deep injection of waste chemicals into the Colorado Rockies in the 1970s, and that operation was associated with temblors.
The optimistic view is that these temblors result from strains in the rock strata being released by the lubricant of the injected materials. By that logic, the temblors are releasing strains that would otherwise accumulate until they eventually produced a serious earthquake.
No one has been killed, or even seriously injured, by an earthquake near a geothermal site.
Still, the precautionary view might be that induced geothermal sites should be demonstrated in sparsely settled areas that only have wood frame houses (which are much more resistant to earthquake damage than major cities. Furthermore, some of these sites should be large power plants to check orders of magnitude large power plants.
Might it be worth the expense? The answer is, most emphatically yes. At best, testing would prepare the way for a major energy initiative. At worst, humanity would be warned away from a dangerous line of development.
Geothermal energy, tapping into the fission heat of the Earth’s core, has the potential to supply a major part of humanity’s energy needs without major outputs of carbon dioxide. Those possibilities got both good news and bad news in mid September 2009.
The good news was provided by ETH Zurich (Switzerland) who have done the basic research for a thermal drill to penetrate rock with potential for providing geothermal energy. Drilling is typically one of the greatest costs for geothermal energy, and indeed, any place on Earth could provide geothermal energy if drilling costs were low enough.
In fact, drilling costs for geothermal tend to be high for two reasons. First, except for a rare geologic sites, deep drilling is required. Second, heat (by definition) tends to be in igneous (that is volcanic-type) rocks, or at least metamorphic (sedimentary rocks that have been cooked by nearby magma). Such rocks tend to be harder and thus slower to drill through for the conventional rotary drills developed for oil drilling.
One approach from several decades ago was an electrically heated drill head that actually melted its way through the rock. This was an energy-intensive process, and it was not particularly fast.
The ETH researchers are developing a system for providing ethanol, oxygen, and water at supercritical pressure and temperature, and then succeeding in igniting them (Science Daily, http:www.sciencedaily.com/release/2009/090912144809.htm). The resulting temperature does not melt the rock; rather, the heat difference between the flame front and the rock further back causes spalling at the flame front, and chips of rock fly off. The flow of reaction products carries the chips away. In fact, the ETH researchers want to avoid melting rock because melting results in slower drilling speeds.
Caveat: Granted, this process has been tested in an exotic high-pressure chamber; however, it has not yet been used on an actual drilling operation. Real operations could have presently unknown problems. For example, fracturing of rock might cause major drops in pressure, thus losing the high-pressure needed for the supercritical flame front. Actual demonstration projects are needed to develop working flame drills.
Meanwhile, New Scientist was one of the journals describing a worrisome side effect of geothermal power production (Sept. 16, 2009, http://www.newscientist.com/article/dn17795-geothermal-power-quakes-find-defenders.html). The New Scientist article reported that Landau in the province of Rhineland-Palatinate had suffered a 2.7 magnitude quake near its geothermal power plant. This is a facility in which a hole was drilled into hot rock and steam was injected. A Swiss facility using this method also had small earthquakes. This echoes the deep injection of waste chemicals into the Colorado Rockies in the 1970s, and that operation was associated with temblors.
The optimistic view is that these temblors result from strains in the rock strata being released by the lubricant of the injected materials. By that logic, the temblors are releasing strains that would otherwise accumulate until they eventually produced a serious earthquake.
No one has been killed, or even seriously injured, by an earthquake near a geothermal site.
Still, the precautionary view might be that induced geothermal sites should be demonstrated in sparsely settled areas that only have wood frame houses (which are much more resistant to earthquake damage than major cities. Furthermore, some of these sites should be large power plants to check orders of magnitude large power plants.
Might it be worth the expense? The answer is, most emphatically yes. At best, testing would prepare the way for a major energy initiative. At worst, humanity would be warned away from a dangerous line of development.
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