Since 2009, earthquakes in the Delaware Basin, a prolific oil-producing region in West Texas and New Mexico, have been on the rise. The majority of them, according to a study led by researchers at The University of Texas at Austin, can be linked to oil and gas production.
The researchers examined data from 2017 to 2020 that tracked seismicity and oil and gas production in the region and discovered that 68 percent of earthquakes above magnitude 1.5 were strongly associated with one or more of the following oil and gas production activities: hydraulic fracturing or disposal of produced formation water into either shallow or deep geologic formations. All subsurface reservoirs contain formation water, which is produced alongside oil and gas. Produced water is disposed of by companies injecting it into geologic formations separate from oil and gas reservoirs.
According to the study's co-author, Alexandros Savvaidis, a researcher at the UT Bureau of Economic Geology and the principal investigator of Texas' state seismic monitoring network and seismicity research TexNet, all of these production activities are known to increase subsurface pore pressure, which is a mechanism for triggering earthquakes. The study was able to determine which activities are linked to past earthquakes by combining statistical analysis and physics-based modeling.
"This paper demonstrates that we now know a lot about how oil and gas activities and seismic activity are related," said Savvaidis. "Modeling techniques could assist oil and gas producers and regulators in identifying potential risks and adjusting production and disposal activity to reduce them."
The researchers examined approximately 5,000 earthquakes and chose the magnitude 1.5 or greater threshold. Injection into shallow sedimentary formations above the hydraulic fracturing depth was linked to 43 percent of earthquakes above magnitude 1.5; 12 percent were linked to injection into deep sedimentary formations above the basement rock but below the hydraulic fracturing depth. The magnitude 5.0 earthquake in Mentone, Texas, in 2020, occurred in a region where seismicity was strongly associated with deep-produced water injection.
Only 13% of earthquakes were linked to hydraulic fracturing, a process that uses highly pressurized fluid to create and enhance fractures in the rock to increase the flow of oil and gas. However, this was higher than anticipated.
The model divided the Delaware basin region into five-kilometer squares (about three miles), with researchers examining the relationships between seismicity, oil and gas activity, and subsurface pore pressure for each square over time.
The model was created by a postdoctoral researcher at the UT Jackson School of Geosciences, where a bureau is a research unit. The model was first used in a 2020 study that discovered a link between produced water disposal and earthquakes in Oklahoma.
"We believe the framework presented in this study is applicable to other regions around the world that may be experiencing seismicity associated with subsurface fluid injection operations," said Grigoratos, now a postdoctoral researcher at ETH Zurich.
According to the researchers, TexNet played an important role in the research by providing around-the-clock seismic monitoring across the state. TexNet also recently launched an online tool for oil and gas operators to voluntarily report data on produced water injection, supplementing the information available in national registries.
"Although there is still much to learn and more work to be done, particularly in terms of mitigation and forecasting," said Scott Tinker, the bureau's director and a governor-appointed member of the TexNet Advisory Committee. "This knowledge enables academics, regulators, and industry to collaborate in order to mitigate and minimize risk." It is the type of coordination required in many types of industrial operations. I am pleased to see Texas in the lead."
The TexNet program of the state of Texas funded the study. Ellen Rathje, a professor at the University of Texas Cockrell School of Engineering, is also a co-author of the study.
Journal Seismological Research Letters.