The process of extracting energy-providing
oil and natural gas from shale and sand nestled below the Earth’s surface could
become a more exact science that produces more power and drives higher profits thanks to work by Pitt researchers.
Adjunct assistant professor of
Kumar and professor William Harbert
of the Department of Geology and
Environmental Science worked with the Department of Energy’s National
Energy Technology Lab researcher Richard Hammack to develop advance geophysical
workflows for detecting low-frequency earthquakes that shed light on the types
of rock deformation that occur during hydraulic fracturing. This knowledge can
be used to increase the amount of oil and natural gas that can be produced from
unconventional shale reservoirs.
The previously undetected resources
could be a windfall for an industry expected to produce an average of 90.3
billion cubic feet per day of dry natural gas this year and an average of 92.2
billion cubic feet of natural gas per day by 2020, according to the U.S. Energy
“This work answers a very
important question, which is, when you do hydraulic fracking, where exactly is
the energy going?” said Harbert.
Hydraulic fracturing, also known
as fracking, is the process where mixture of water, sand and chemicals are pumped under
high pressure into strategically drilled underground wells. Typically,
explained Kumar, companies conduct the process in ways that are designed to create
new fractures and increase the connectivity of preexisting fractures that leads
to instantaneous improvement in fluid flow.
“During the fracturing process, large
numbers of small magnitude earthquakes are generated that are recorded by
surface and/or borehole geophones. Based on the location of the microseismic
earthquake, you can try to create a picture of overall volume of rock that’s
been fractured. Based on that volume, companies can anticipate how much oil and
gas they are going to produce,” Kumar said.
For years, conventional wisdom
has been that shale reservoir rocks will show signs of instantaneous fracturing
due to high-pressure fluid injection, which is known as brittle deformation.
However, research by Kumar, Harbert, Hammack and former NETL intern Erich Zorn,
now a Senior Geologist at DiGioia Gray & Associates, has indicated that rocks with higher contents
of clay and other soft materials dominantly undergo non-brittle deformation,
which is characterized by slow rate of fracturing over longer periods of time
and release ultra low-frequency earthquakes.
They detailed the findings in the paper, “Long Period, Long Duration (LPLD) Seismicity
and their Probable Role in Reservoir Stimulation and Stage Productivity” which is recently
published in the journal SPE Reservoir Evaluation & Engineering.
“We found positive temporal
correlation between low frequency earthquakes and increased fluid activity
during hydraulic fracturing, suggesting that these unique events are generated in response to extensive reservoir fracturing,
triggered by highly elevated fluid pressure,” Kumar said. “These low
frequency seismic events of long duration are likely linked with non-brittle
deformation in the reservoir during hydraulic fracturing and contribute both in
the overall stimulation of the reservoir and gas production,” said Kumar.
Additionally, during field
research at a West Virginia hydraulic fracking site, Kumar demonstrated the
low-frequency earthquakes that signal non-brittle deformation and potential stimulation
of reservoir could be detected using low-cost surface seismometers placed on
the ground rather than borehole geophones and fiber optic sensors, which are
much more expensive and requires a well to be drilled specifically for
Combined, the findings could give oil
and gas industry executives more precise methods to extract greater amounts of
energy, cheaper equipment to get the process started and a broader view of the
types of areas that are worthy of exploring.
“Our analysis proposed that overall
deformation due to hydraulic fracking doesn’t belong to one particular type of
deformation, it undergoes both types, brittle and non-brittle,” said Kumar. “Taking
both into account can increase overall estimates of fracturing volume of rock,
therefore estimate of oil and gas productivity will be much higher.”
Hammack said the theory still
needs to be proved at other well-characterized sites that feature geophysical
models and he’s hoping the team will be able to monitor less-characterized
areas near Pittsburgh and Morgantown sometime this year.
And while he credited the work of
Stanford University geophysicist Mark Zoback for the first work involving low-frequency
earthquakes in shale gas wells, he said Kumar’s work with surface seismometers
helped to advance that to new heights.
“No one else had ever gone the lengths to build
a whole new science behind it,” Hammack said.