November 11, 2019
In addition to producing oil and gas, the energy industry produces a lot of water: about 10 barrels of water per barrel of oil on average. New research led by The University of Texas at Austin has found that where the produced water is stored underground influences the risk of induced earthquakes.
Beyond supporting the link between water disposal and induced seismicity, the research also describes factors that can help reduce earthquake risk.
“If we want to manage seismicity, we really need to understand the controls,” said lead author Bridget Scanlon, a senior research scientist at UT’s Bureau of Economic Geology.
The research was published Oct. 31, 2018, in the journal Seismological Research Letters. Co-authors include Matthew Weingarten, assistant professor at San Diego State University; Kyle Murray, adjunct professor at the University of Oklahoma; and Robert Reedy, research scientist associate at the Bureau of Economic Geology.
The researchers found that the increased pressure that is caused by storing produced water inside geologic formations raises the risk of induced seismicity. The risk increases with the volume of water injected and the rate of injection, both at the well and regional scale.
Researchers specifically looked at water stored near tight oil plays, including the Bakken, Eagle Ford and Permian shale plays, and Oklahoma overall, which has high levels of induced seismicity in concentrated areas. The study found that, overall in Oklahoma, 56% of disposal wells are potentially associated with earthquakes. The next highest is the Eagle Ford Shale, where 20% of wells are potentially associated with earthquakes.
The study reported that the levels of induced seismic activity relate to, among other reasons, how the water is managed and where it is stored. In Oklahoma, the tendency to store water in deep geologic formations has increased the risk. In the other areas, water is stored at shallower depths, which limits exposure to potentially risky faults.
The findings are consistent with directives issued by the Oklahoma Corporation Commission in 2015 to mitigate seismicity, including to reduce injection rates and regional injection volumes by 40% in deep wells. This study confirmed the changes resulted in 70% fewer earthquakes over a magnitude 3.0 in 2017 compared with the peak year of 2015.
This shows that subsurface management practices can influence seismic risk. However, Scanlon said there can be trade-offs For example, shallow disposal may help lower the risk of earthquakes, but it could increase the risk of the produced water contaminating overlying aquifers.
“There’s no free lunch,” Scanlon said. “You keep iterating and doing things, but you must keep watching to see what’s happening.”