Some people incorrectly think hydraulic fracturing — fracking — is responsible for the increase in earthquake activity in Oklahoma and Texas.
Scientists, however, believe the quakes are caused by the use of underground injection wells to dispose of oil and gas wastewater.
The increase in tremors spurred a coalition of scientists, regulators, industry experts and environmentalists to produce a 148-page report exploring why these earthquakes are occurring and how to prevent future incidents.
In the mid-1960s, earthquakes began to occur in some parts of the country that were using a technique called enhanced oil recovery, which involves pumping water into an oil formation to increase the amount of oil recovered by “flooding” the oil out of the rock.
On rare occasions, the technique caused tremors because secondary recovery operations often entailed large arrays of wells injecting fluids at high pressures into small confined reservoirs with low permeability.
Studies investigating the link between EOR and seismicity found the risk posed by induced earthquakes can be mitigated by careful control of the specific activity responsible for the induced seismicity.
Seismicity can eventually be stopped by either ceasing the injection or lowering the pumping pressures.
Similar safety procedures have been recommended for the wastewater disposal wells linked to tremors in Oklahoma and Texas.
The U.S. Geological Survey reports there are more than 35,000 injection wells used to dispose of oil and gas wastewater in the United States, and only a few dozen have been linked to any sort of felt seismic activity.
Taking precautions such as avoiding disposal near fault lines, installing pressure monitors in these wells, reducing the volume and pressures at which fluids are injected into these wells and perhaps shuttering specific wells entirely can greatly reduce the risk of additional tremors.
With scientists and engineers decades ago having figured out how to prevent earthquakes when injecting water into oil formations during enhanced oil recovery operations, one might well wonder why such earthquakes are still happening in Oklahoma and Texas.
Unsurprisingly, geology is the key factor determining why certain areas are more prone to quakes than others.
Injection wells are used at high volumes in Michigan, North Dakota and other areas yet have not resulted in any felt quakes, whereas a few wells operating under similar volumes in Oklahoma have brought an increase in tremors.
The specific factors making wastewater disposal in Oklahoma more of a risk than the same activity in North Dakota will take time to figure out, as the unique geology of each region complicates the issue and makes a “one-size-fits-all” regulatory approach a poor response.
Understanding the historical relationship between induced seismicity and oil and natural gas production is important for scientists and state regulators because it provides a road map for determining the causes of the current tremors and a toolbox of approaches to limit their occurrence in the future.
