Induced Seismicity in the Bakken: Much Ado about Almost Nothing

Abstract:

This study investigates possible links between seismicity and wastewater injection in the Williston Basin and Bakken Formation in North Dakota and Montana. To identify Bakken earthquakes we analyzed seismic records collected by the EarthScope USArray temporary network of seismograph stations, deployed on a grid with 70-km spacing.

During the September 2008 – May 2011 study period we identified only nine earthquakes; of these only three were near injection wells. Thus, possibly triggered earthquakes are rarer near injection wells in the Bakken than in the Barnett Shale of Texas, or in central Oklahoma.

The reason why Bakken earthquakes are so scarce is unclear. In many respects the Bakken/Williston region is similar to the Barnett Shale/Fort Worth Basin of Texas. In both regions injection volumes increased significantly in late 2007, and both areas have low levels of natural seismicity. Yet, in Johnson and Tarrant counties in the Barnett, earthquakes near injection wells were numerous; in the Bakken and elsewhere in the Barnett, earthquakes near wells were scarce.

An important result of these surveys is that the relationship between seismicity and injection/production activities varies considerably in different geographic areas. In the Bakken and western counties of Texas’ Barnett Shale, there is almost no seismic activity near injection wells. In Oklahoma, Arkansas, parts of the Barnett, and near Timpson in east Texas, there are earthquakes associated with high-volume injection wells. In the Eagle Ford of Texas earthquakes are associated primarily with production (not injection). And near Snyder, TX, recent earthquakes are associated with CO₂injection.

This variability in response to injection complicates efforts to craft uniform policies or regulations to mitigate potential seismic hazards associated with injection practices. At a minimum it suggests that within particular geographic regions it is important to survey the relationship between seismicity and injection before considering possible policy responses or regulations. For these regional surveys, the records collected during the two-year deployment of USArray stations are valuable, although these may need to be augmented by continuing coverage.

Figure: Earthquakes, explosions, injection wells, and coal mines in the Bakken (shaded area).