Sandia LabNews

Sounds of drilling heard again at Mammoth Lakes

For the first time since 1993 the sounds of drilling in the Long Valley Exploratory Well near Mammoth Lakes, Calif., are being heard as researchers resume their quest to discover how deep magma flows under the tree-lined mountain terrain.

�We will be doing core drilling and expect to come away with some important scientific information as well as a determination of the potential use of magma heat energy for such real applications as generating electrical power,� says John Finger of Geothermal Research Dept. 6211, who serves as project co-manager with colleague Ron Jacobson.

John and Ron are living and working at Mammoth Lakes between July 15 and the end of September during the third phase of the drilling project.

Drilling of the Long Valley Exploratory Well reaches deep into the earth in an attempt to locate magma (molten rock). Once the location of the magma is pinpointed, the well could become an engineering laboratory for testing prototype systems and materials for exchanging heat with magma. It may also provide valuable information about earthquake activity in the area.

Three phases
Phase one of the project started in 1989 as part of the DOE Magma Energy Program, drilling to a depth of 2,568 feet. It was initially conceived as a magma energy well to be drilled in four phases to either a depth of 20,000 feet or a temperature of 500 degrees C, whichever came first. DOE canceled the program in 1990 but funded the second phase in 1991, which drilled to 7,588 feet in an effort to advance conventional geothermal exploration.

During this third phase, researchers hope to reach 12,500 feet � still a considerable distance from the magma, which is believed to be somewhere between 18,000 to 26,000 feet. This closer approach is expected to result in a much better estimate of the magma�s depth.

�The reason we are so interested in this area is that it is one of only three major volcanic calderas [craters formed after volcanoes erupt] 10 miles or more in diameter in the US that are still young enough to contain magma close to the surface,� John says. �Long Valley has had the most recent volcanic activity [the last eruption was 550 years ago], and there is extensive geophysical evidence of magma�s presence.�

The magma is physically close enough to reach using standard drilling methods, making it ideal for research.

If magma is ever reached, a heat exchanger could be inserted into it for long-term experiments. The heat exchanger, operating as a radiator in reverse, would use the magma to heat a liquid, which would then be pumped to the surface where the heat could be used for industrial processes or to generate electricity.

Since 1991, however, drilling at the Long Valley Well has been curtailed due to lack of funding. Some remedial work was done in 1993 to correct problems from the 1991 drilling, and a few seismic studies were conducted at about 6,600 feet.

Project back on track
Now, seven years after the last major drilling operation, the project is back on track, thanks to fund-raising efforts by John, Ron, John Sass of the US Geological Survey, and Dan Lyster, a representative of Mono County, Calif., where Mammoth Lakes is located. They obtained support from four organizations � the California Energy Commission, US Geological Survey, DOE, and the International Continental Drilling Program (ICDP), based in Potsdam, Germany � putting together a $2 million funding package.

Each entity, John says, has its own particular interest in the project. The California Energy Commission, DOE, and Mono County want to learn more about the role the Long Valley Caldera can play in the energy future of the area. Three geothermal power plants several miles south of the well now produce about 40 megawatts of electrical power. If sufficiently high temperatures and permeable rock are found, the Long Valley dome could provide enough fluids for a fourth geothermal plant. And if high temperatures exist, but the rock is impermeable, the site could still be a candidate for a electricity production, using a technique called hot-dry-rock. Sandia�s Geothermal Research Department will also have the opportunity to test several newly designed pieces of equipment in a realistic field environment.

The primary interest of the US Geological Survey is in the volcanic hazard posed by the caldera and neighboring Mammoth Mountain. The volcano first erupted 700,000 years ago with a major explosion, and it has remained active over the centuries. The current era of unrest began with an intense swarm of earthquakes, including four of magnitude 6, in 1980, and has continued at varying levels. During recent months earthquake activity has increased dramatically; the area experienced a 5.1 earthquake several weeks ago. Also, the caldera�s dome has risen sporadically over the past 12 to 15 years. In fact, the area where the drill rig is located has risen three feet since 1986.

The recent activity of the area has captured the interest of the international earth science community, and hence the support of the ICDP. The drilling project will be tied to the ICDP�s Drilling Information system. Daily drilling reports, digital core images, and other scientific information will be regularly fed into the system during and after drilling and will be available on the Web.

Third venture different
�This drilling venture will be different from the previous two,� John says. �During phases one and two we employed drilling techniques found in oil well drilling, using a rotary drill that crushed rock. We did some core drilling at the end of each phase. This time we will drill a continuous core, which will be brought up to the surface for study.�

And though the temperatures are expected to increase � possibly reaching as high as 350 degrees C, still considerably below the 900 degrees C temperature of magma � no �exotic� materials will be needed for the drill bits and other drilling equipment. The reason, John says, is because water is constantly circulating through the drill, keeping it cool.

Throughout the drilling process, bottom-hole temperatures and pressures will be obtained with a data logger. Depending on hole conditions, fluid samples may also be obtained. Upon completion, a steel liner will be left in place to allow a series of temperature logs over the next nine months.

Well to be reconfigured in 1999
During the summer of 1999 the well will be reconfigured as a downhole volcanological observatory for the US Geological Survey and other research institutions. The instruments to be used are still in the early design stages but will probably include seismometers to determine seismic activity and devices for monitoring water level, temperature, and strain.

The Long Valley Exploratory Well is one of very few research activities in the world drilling in a young caldera and studying the use of magma heat to generate electricity. Very hot wells have been drilled in Japan, Iceland, Indonesia, and other seismically active places, but, except for preliminary investigation by Shell International, no other work on magma is known to be underway.

John says information provided from this third phase will be valuable from two standpoints, energy and science.

�From the energy point of view, we may be able to determine if this is a realistic concept, � John says. �It would make a large difference whether the magma is 18,000 feet deep or 26,000.�

From the science standpoint, information may be obtained about how the calderas evolve and how they affect seismic activity.

�This drilling project is exciting because we are doing something unique and are satisfying the goals for a diverse group of customers � science, energy, and technology development,� John says. �We are eager to see what we will learn from this third go around.�