DOE-funded Seismic Tool Guides First Deep Well through San Andreas Fault

A newly commercialized Department of Energy–funded technology developed to aid the exploration and production of natural gas and oil has enabled researchers for the first time to drill through and observe an active portion of California's notorious San Andreas Fault.

The San Andreas fault—the boundary between the earth's Pacific and North American tectonic plates—is over 800 miles long and 10 miles deep. For years, scientists have speculated that it could be the source of the next major earthquake to hit California, with the epicenter likely near the small town of Parkfield in California's coastal mountain range.

With the help of new vertical seismic profiling technology, scientists have created an earthquake observatory two miles deep in a seismically-active section of the fault where earthquakes originate. The technology, developed with DOE funding by Brea, Calif.-based Paulsson Geophysical Services Inc., produces high-resolution, three-dimensional subsurface images.

The San Andreas Fault Observatory at Depth (SAFOD) is a borehole observatory for directly measuring the conditions under which earthquakes occur. The project is funded by the National Science Foundation and led by a team of scientists from Stanford University and the U.S. Geological Survey.

To locate the earthquake-prone portion of the fault, the team used Paulsson's 80-level borehole seismic receiver array, which is essentially a string of instruments for gathering subsurface seismic signals from within a borehole. The array, the world's longest, recorded over 1,000 earthquakes, including many events too small to detect on conventional seismographs positioned on the ground. The tool also was used in an active-source experiment that imaged in three dimensions the location and configuration of the San Andreas Fault at depth. All of this information was used to guide the SAFOD well across an active portion of the fault.

Phase 2 drilling began on June 13, 2005, and in August, the well penetrated the San Andreas Fault, setting the stage for decades of direct observation of earthquakes in their formative stages.

This is an example of a Department of Energy project that clearly has benefits outside the energy sector. Technology developed to make detailed three-dimensional maps of subsurface oil and natural gas deposits was used to steer a long-term earthquake research well. Information from the well will help scientists develop models for the San Andreas Fault that ultimately will lead to better safety plans for communities along the fault.

The oil and gas industry also quickly saw the value in what amounts to a quantum leap forward in vertical seismic profiling—already deemed the gold standard in seismic surveying.

"It's a big step forward," said Frances Toro, project manager for the National Energy Technology Laboratory (NETL) in Morgantown, W.Va., of the new technology, which was designed to sharpen the resolution of images obtained through vertical seismic profiling and cut downhole time needed to conduct seismic surveys in natural gas exploration and development wells. "The technology offers much better vertical and horizontal resolution of reservoir details when compared with what is possible with existing imaging techniques."

A number of oil and gas companies have deployed Paulsson's technology in major projects in Alaska and the Lower 48 states in recent months.

"The cables have been working flawlessly," Toro noted, adding that the Paulsson technology already has been commercialized without the NETL project moving to the formal demonstration phase. "Industry has been using this technology so much, we haven't been able to conduct a demo."

That underscores two key boons of DOE's gas and oil research program: the rapid commercialization of cutting-edge technologies that benefit America's energy security and the ancillary benefits that flow from applying the new technologies to other areas of scientific endeavor.

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