Seismic activity linked to injection wells may vary by region

March 31, 2015
The US portion of the Williston basin produced fewer earthquakes caused by wastewater injection than basins in Texas, University of Texas at Austin researchers found.


The US portion of the Williston basin produced fewer earthquakes caused by wastewater injection than basins in Texas, University of Texas at Austin researchers found.

Links between seismicity and production activities might vary by region, UT researchers said in a study published in the Seismological Research Letters (SRL).

Oil and gas activities in the Williston basin, underlying parts of Montana, North Dakota, South Dakota, and Canada's Saskatchewan, have evolved in recent years to include hydraulic fracturing and horizontal drilling.

UT scientists used available monitoring data to research for a possible connection between seismicity and production near the Bakken formation, which historically has had few seismic events.

"I'm looking at the relationship between seismicity and industry activity across different geographical areas," said Cliff Frohlich, lead-author of the study and associate director of the UT Institute for Geophysics.

Barnett shale studied

Frohlich previously conducted similar studies, including one of the Barnett shale near Fort Worth, Tex.

He and his colleagues analyzed data recorded by the EarthScope USArray, a National Science Foundation-funded network of temporary broadband seismometers and also statistics from IHS Inc., which compiles industry information using state regulatory sources.

The authors identified nine regional earthquakes in the Williston basin covering 100,000 sq km. Three of the nine earthquakes occurred near active injection wells, suggesting a connection to wastewater disposal.

Using a similar method, Frohlich's previous study of the Barnett shale found significantly greater induced seismicity--55 earthquakes within a 5,000 sq km near Fort Worth.

"Why are earthquakes triggered in some areas and not in others? It's an important question for regulators and the scientific community. Some answers are emerging," said Frohlich.

He cited differences in geology, orientation of pre-existing faults, local fault strength, injection practices, and the timing and duration of oil and gas production as potential factors influencing seismicity.

"Before we implement severe regulations or schemes to manage injection activity in a particular region, we need to do the homework--survey the relationship between seismicity and injection activity there to determine what's warranted," said Frohlich.

The study, "Analysis of Transportable Array (USArray) Data Shows Earthquakes are Scarce Near Injections Wells in the Williston basin, 2008-2011," was published in the March-April print edition of SRL.

In addition to Frohlich, authors include Jacob I. Walter and Julia F. W. Gale of UT-Austin. The Seismological Society of America publishes the journal SRL.

"Before we implement severe regulations or schemes to manage injection activity in a particular region, we need to do the homework--survey the relationship between seismicity and injection activity there to determine what's warranted," -- Cliff Frohlich, lead author of the study and associate director of the UT Institute for Geophysics