The underlying strata and geological formations across Texas have provided an abundance of natural resources, including the recent developments of shale oil and gas resources. The development of these resources, and the attendant seismic and other geological implications of those activities, requires knowledge of the permeability of widely varying geologic formations and subsurface stress regimes and tectonics and how they are affected by hydraulic fracturing processes.
Earthquakes have increased in Texas. Before 2008, Texas recorded about 2 earthquakesa year. Since then, there have been about 12-15 a year.
Some of these earthquakes are linked to wastewater disposal from oil and gas development, not with hydraulic fracturing.
Seismic monitoring stations in Texas will increase from 18 to 43.
Wastewater disposal wells near earthquake locations now must receive special approval from state regulators.
Frequently Asked Questions
Do we know what’s causing all of these new earthquakes?
In some cases, a link has been established between these seismic events and oil and gas development activity, specifically the disposal of wastewater. But what remains unknown is a complete understanding of the physics of that process and understanding how much earthquakes can be mitigated or eliminated. There’s still much that remains unknown: faults are ubiquitous across Texas but remain incompletely characterized.
The majority of known faults present in Texas are stable and are not prone to generating earthquakes. To date, induced earthquakes in Texas have been associated with wastewater disposal wells, not with hydraulic fracturing.
What is being done to address these knowledge gaps?
We need to learn more about where and when earthquakes are occurring. In 2005, there were only six permanent seismographic stations in Texas. By 2015, that number had increased to 17. Soon, thanks to the implementation of the TexNet initiative (a state-funded research project), Texas will have an additional 22 permanent seismic stations in Texas as well as employ 36 portable stations for monitoring local areas of interest, like in the Dallas-Fort Worth area.
These stations will allow us to better monitor earthquakes and better share seismic data. The more that is known about the earthquakes, the better equipped we’ll be to come up with ways to mitigate or avoid induced earthquakes.
Can we do anything to stop induced earthquakes?
If the physics of induced earthquakes can be better understood, criteria can be established for the disposal of wastewater from shale oil and gas production: how far away the disposal must be from a fault, or how much fluid can be disposed. Compared to some other states like Oklahoma, Texas has had a relatively low number of possibly induced earthquakes.
“We know there are earthquakes in Texas and that some of them have been linked to oil and gas operations. But what remains unknown is a complete understanding of the physics of that process that can lead to these earthquakes and understanding the degree we can mitigate or eliminate them.”
~Brian Stump, Southern Methodist University
- Geologic faults are ubiquitous across Texas; these faults are poorly and incompletely characterized.
- The majority of known faults in the subsurface in Texas are stable and are not prone to generating earthquakes.
- There has been an increase in the rate of recorded seismicity in Texas over the last several years. Between 1975 and 2008 there were, on average, one to two earthquakes per year of magnitude greater than M3.0. Between 2008 and 2016, the rate increased to about 12 to 15 earthquakes per year on average.
- Under certain unique geologic conditions, faults that are at or near critical stress may slip and produce an earthquake if nearby fluid injection alters the effective subsurface stresses acting on a fault.
- Mechanisms of both natural and induced earthquakes in Texas are not completely understood, and building physically-complete models to study them requires the integration of data that always will have irreducible uncertainties.
- To date, potentially induced earthquakes in Texas, felt at the surface, have been associated with fluid disposal in Class II disposal wells, not with the hydraulic fracturing process.
- The TexNet goals address an integrated research portfolio that considers seismicity analysis, geologic characterization, fluid-flow modeling, and geomechanical analysis.
- Future geologic and seismological research initiatives should develop improved and transparent approaches that seek to balance concerns surrounding data handling and sharing, and that promote sharing of data.
- Development of a common data platform and standardized data formats could enable various entities collecting data to contribute to better data integration. It also could facilitate interdisciplinary collaboration directed toward mitigation and avoidance of induced seismicity.
Brian Stump (Lead)
Southern Methodist University
ExxonMobil Upstream Research Company
Railroad Commission of Texas