Originally published on Forbes.com on September 19, 2021

If the exponential growth of earthquakes continue, mitigation efforts will need to be imposed in the Delaware basin.

Earthquakes are increasing rapidly in the Delaware portion of the Permian basin which is located in southeastern New Mexico and crosses over the southern border into west Texas.

This growth, which is exponential since 2015, is reminiscent of earthquakes in Oklahoma that reached their peak in 2015, and caused quite a scare in the state.  Later they were shown to be earthquakes induced by disposal wells that were getting rid of massive amounts of produced water — dirty water that comes up with oil or gas in production wells.

In Oklahoma, the produced water was injected deep underground and from there it permeated into the basement rock which is often highly faulted. The water pressure, if it meets a critically-stressed fault, can trigger fault slip and an earthquake. The same situation no doubt exists in the Delaware basin.

For every barrel of oil produced from a well in Oklahoma, 7 – 20 barrels of water were produced. In the Delaware basin the ratio is 3-10 water/oil.

Figure 1. 235 M > 3 earthquakes in Delaware basin from 1 January 2009 – 12 September 2021. Source: USGS.

The 235 M > 3 earthquakes in the Delaware since 2009 are shown in Figure 1. The majority are in Texas, not New Mexico. These quakes are generally attributed to injection of produced water by disposal wells.

Permian oil production started to grow after 2011 when the new-technology fracking of long horizontal wells appeared. Production flattened for a year in 2015 but then accelerated rapidly in 2017 and 2018. More oil and gas wells mean more produced water to be disposed.

A rapid uplift in produced water in the Permian is consistent with more earthquakes connected with disposal wells, and reflects an active drilling campaign in the Delaware portion of the Permian basin.

Figure 2. Produced water in several shale plays. Data for Oklahoma is state-wide. Source: ResearchGate.

In 2017, the Permian as a whole produced 63 billion gal or 1.5 billion bbl per year (Figure 2). A large fraction of this was injected in disposal wells. This enormous volume of water was as much as Oklahoma produced in 2015 when that state recorded 890 earthquakes of M > 3.

There are hints that Texas below the border of New Mexico is double-dipping their earthquake risk because produced water from New Mexico is trucked across the border to Texas disposal wells. If the earthquake risk continues to increase in the Delaware basin, New Mexico may not be happy because its produced water has been shipped and disposed interstate rather than recycled, which is the state’s intention.

An exec for a water recycling company said about 200 disposal wells in Texas that lay within 10 miles of the New Mexico line argued for a connection between the disposal wells and growing seismicity.

How do the earthquakes compare with Oklahoma?

The big question is, are the earthquakes in the Delaware mirroring what happened in Oklahoma? And do the states’ regulators need to get involved like they did in Oklahoma to mitigate the earthquakes?

Let’s look at the time profile of earthquakes in the Delaware, of magnitude M > 3. These are ones than can be felt at the surface. Figure 3 shows that after moderate increases in 2015-2019, earthquakes grew more frequent in 2020 and 2021. Most of the quakes in 2021 occurred in the first clump of Figure 1 – just below the New Mexico border.

This behavior is similar to the earthquake history (M > 3) in Oklahoma shown on Figure 3 – five lower level years before two higher level years.

The peak rate was 890/year in 2015 before declining due to regulation and well shut-ins as oil price fell (the decline is truncated in the figure but did begin in 2016).

Figure 3. Earthquakes M > 3 are shooting up in Delaware basin (left panel). Earthquakes in Oklahoma (right panel). Source: USGS.

Shifting Oklahoma data forward by 6 years gives an “eyeball match” to compare the data in Figure 4. The right panel, using a logarithmic scale shows earthquake numbers at both locations are rising exponentially at the same rate of increase.

But earthquake numbers in Delaware are lower than in Oklahoma. This could be because less water has been disposed in the Delaware, or there are fewer locations of fault-lines that are triggered by water disposal.

Still, the same exponential rate of increase should be a concern in the Delaware – because it suggests that in years 2022 and 2023 earthquake numbers could rise to levels similar to 585/year and 890/year as observed in Oklahoma.

Figure 4. Left panel uses an “eyeball match” time shift of 6 years to compare the data. Right panel is log plot of same data. Source: USGS.

Takeaways.

Earthquakes in the Delaware basin are bunched in two local areas (Figure 1), possibly where fault lines are situated. Most of the earthquakes are in Texas, but larger ones, M > 4, have been felt in New Mexico.  

In the Delaware basin, seven M > 4 quakes have surged in 2021 with only two other M = 4 events in 2015. Six out of seven of these events had their epicenters in Texas, in the clump of quakes just below the border with New Mexico in Figure 1.

The data comparison with Oklahoma (Figure 4) shows a similar exponential increase of earthquakes with time in both locations. This suggests earthquakes in the Delaware may continue an exponential increase to higher levels as experienced by Oklahoma in 2014 and 2015 (up to almost 1,000 quakes per year).

This is an unnerving interpretation because more and more M > 4 quakes would occur and even a few dangerous M > 5 quakes. A history of the Oklahoma earthquakes is given elsewhere.

The US Nuclear Regulatory Commission (NRC) has evaluated a proposal by Holtec International to build a storage site for radioactive nuclear waste in the middle of hundreds of oil and gas wells in the New Mexico portion of the Delaware basin. The figures above support the case that the Permian basin may not be the best place to store nuclear waste.  

Earthquake mitigation. 

Adrienne Sandoval, director of the State’s Oil Conservation Division, said OCD connected seismicity to water disposal on the New Mexico portion of the Delaware basin.

“We don’t want any earthquake activity that could threaten property or people in any way. The larger the earthquake, the larger the potential for impacts so we want to mitigate that.”

If the exponential growth of earthquakes continue, mitigation efforts will need to be imposed in the Delaware basin, such as:

• Limiting total disposal volumes per well.
• Injecting further away (shallower) from the basement, where these earthquakes occur (earthquake depths are 15,000-27,000 ft in Delaware basin).
• Monitor seismic activity and shut-in in disposal wells in the vicinity of intense earthquakes (fault lines).
• Switch from well disposal to recycling of produced water that can be used in fracking of future wells. This would save a lot of aquifer or city water that has been used in the past – a football stadium of water up to 40 feet over the grassed area is needed to completely frac a new-technology shale well. Recycling is happening in the Delaware basin but needs to be accelerated.

If the exponential increase continues it may lead to M > 5 earthquakes as were recorded in Oklahoma. The largest was the Pawnee quake at M = 5.8 on September 3, 2016. An earthquake of this size can create serious damage to buildings, as has happened in other magnitude 5 quakes in Oklahoma.