'Thumper' Trucks Shake out Marcellus Shale Details
Valley News-Dispatch
4 October 2010
By Chuck Biedka
A Texas company is shaking things up locally to get information about
Marcellus Shale and other underground rock formations.
Dawson Geophysical of Midland is using hydraulic equipment mounted on
three large trucks driven in tandem to "thump" the Route 780 road
surface.
Then, using sonar and 18 sensors that are put out every 110 feet from
each truck, the company charts the vibrations as they bounce off the
formations deep in the earth.
A map of sorts shows a two-dimensional, up-and-down view of the
subsurface.
The map shows Marcellus Shale and other rock formations a 1 1/2 miles
below the sensors, said Matt Leist, Dawson Geophysical's regional
manager.
The company is doing the work for Evans Geophysical Co., which is
assembling seismic data for a very large, multi-state subsurface map of
the Appalachian Basin -- home to the Marcellus formation and others
where natural gas can be found.
Company President Annette Evans said her Suttons Bay, Mich., seismic
data brokerage company has already obtained data for about 2,000 miles
of formations in parts of New York, Kentucky and West Virginia as well
as Pennsylvania.
Geologists and others will interpret the results and decide where to do
more tests.
The "vibroseis method" is the formal name for the testing being
performed, but it's commonly referred to as the "thumper" method.
"Vibroseis is a lot easier than using explosives, and you can use it on
roads and the quality is very good," she said.
Dawson Geophysical obtained permits from PennDOT to do the vibration
tests along the Route 56 bypass and Route 780 in Lower and Upper
Burrell. Tests started in the summer along Route 56 and are continuing
along Route 780.
Other Dawson crews are doing the same tests along Route 31 near Mount
Pleasant in the southeastern part of Westmoreland County.
Leist said trucks cover five to six miles a day. It takes some time,
but the crews work steadily.
The technicians place the sensors, start vibrations and begin taking
measurements. After collecting the data, they move down the road and
begin again.
"We only not work when there is bad weather. We can't get good readings
in rainy or windy conditions," he said.
WHAT OTHERS SAY
PennDOT officials said they have issued vibroseis test permits for
several years.
"I'm not aware of any problems," said District 12 permits engineer Rick
Marker. "We've not had any complaints."
Only Dawson Geophysical and Cougar Land Services, of Stafford, Texas,
have received the permits.
The companies don't have to post a surety bond, but "they are required
to have a certificate of insurance in case of damage," Marker said.
A state Department of Environmental Resources geologist concluded there
"never has been any evidence that the vibrations cause harm to the
environment or roads," said DEP spokeswoman Katy Gresh.
Steve Hovan, who chairs Indiana University of Pennsylvania's geoscience
department, said vibration testing is a "common and accurate" method to
obtain information about the subsurface.
He said it's useful for companies looking to drill wells into the
Marcellus Shale formation because it's usually very deep in this area.
Hovan said companies map the region's subsurface to get an idea where
the Marcellus formation can be found -- and where it likely will be
easiest to reach. The information is sold to gas-well drilling
companies.
"The tests aren't new," said John Asma, a spokesman for the
Houston-based Global Geophysical Co.
Vibration tests have been used by the companies since the 1960s, he
said.
For tests in the field, technicians can still drill 20-foot deep holes
and insert dynamite to send out the shock waves to measure, he said.
Chuck Biedka can be reached at cbiedka@tribweb.com or 724-226-4711.