Spring Break
Sizing up seismic activity
By: Julie Rambin
Issue date: 6/25/09 Section: News
Chesapeake Energy, the company responsible for much of the drilling in Cleburne, denies any connection between drilling and earthquakes.
"Often earthquakes are located many miles below drilling sites," said Chesapeake Energy public relations manager Jerri Robbins. "There is no proof yet that drilling activities and seismic activities are related."
However, drilling and seismic activity can be related, according to some geophysicists.
"The shale is pretty brittle. [Drilling] changes the pressure from the natural gas field to the rock itself," said Christopher Mathewson, a Texas A&M University regents geophysics professor. "So the rock fails."
Earthquakes are comparable to a whoopee cushion, Mathewson said.
"When you sit on it, you increase the load at the surface to the point that you push the air out of the cushion. When you're expelling the air from the cushion, you're sinking further into the seat," Mathewson said. "You moved down, didn't you? That's subsidence, because of the change of pressure."
Subsidence is the downward movement of a field, Mathewson said, and this term is more appropriate for the Cleburne earthquakes.
"They're caused by changing the stress," Mathewson said. "They're not associated with a major fault displacement."
The seismic events in Cleburne may continue and might augment the available quantity of gas in a particular field, Mathewson said.
"Sometimes the rock breaks and it increases the amount of gas you can get out of them," Mathewson said. "So gas producers like them."
Though no damage has resulted, it is still necessary to learn more about the unexpected seismic activity, Hayward said.
"If I were in the town, I would not be particularly worried about them," he said. "The big question is, how deep are they? One of the reasons we're doing the study is to find out."
"Often earthquakes are located many miles below drilling sites," said Chesapeake Energy public relations manager Jerri Robbins. "There is no proof yet that drilling activities and seismic activities are related."
However, drilling and seismic activity can be related, according to some geophysicists.
"The shale is pretty brittle. [Drilling] changes the pressure from the natural gas field to the rock itself," said Christopher Mathewson, a Texas A&M University regents geophysics professor. "So the rock fails."
Earthquakes are comparable to a whoopee cushion, Mathewson said.
"When you sit on it, you increase the load at the surface to the point that you push the air out of the cushion. When you're expelling the air from the cushion, you're sinking further into the seat," Mathewson said. "You moved down, didn't you? That's subsidence, because of the change of pressure."
Subsidence is the downward movement of a field, Mathewson said, and this term is more appropriate for the Cleburne earthquakes.
"They're caused by changing the stress," Mathewson said. "They're not associated with a major fault displacement."
The seismic events in Cleburne may continue and might augment the available quantity of gas in a particular field, Mathewson said.
"Sometimes the rock breaks and it increases the amount of gas you can get out of them," Mathewson said. "So gas producers like them."
Though no damage has resulted, it is still necessary to learn more about the unexpected seismic activity, Hayward said.
"If I were in the town, I would not be particularly worried about them," he said. "The big question is, how deep are they? One of the reasons we're doing the study is to find out."
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