There is a whole lot of shaking going on in West Texas. The number of earthquakes above 3.5 magnitude has increased dramatically over the past 2 years. When I lived in Southern California, we wouldn’t get out of bed for anything less than a 5.0, but this seismicity was enough to get the Texas Railroad Commission’s (RRC) attention. It responded by restricting saltwater injection in select seismic response areas (SRA). Details can be found in this issue’s Exploration & Development (E&D) section (p.38), but in summary the RRC put the hammer down on saltwater injection around Midland-Odessa in late September 2021 and followed up in October by implementing restrictions farther west in the Northern Culberson-Reeves SRA.
This response raised more than a few eyebrows, not only for concern about produced water volumes taken off the injection disposal market, but also for RRC’s identification of saltwater disposal (SWD) as the main culprit in the new seismic activity.
If one looks closer, however, both concerns are not as dramatic as they appear. SWD injection has been reduced by about 50% for shallow and moderately shallow wells, which sounds significant, but a 50% cut in allowable injection volume still leaves far more injection volume than had been injected pre-restriction. There still is plenty of headspace for injection, and the new restriction only affects a single moderately shallow well in the Gardendale SRA. Deep injection wells, however, are another story. The new restrictions reduce incremental injection volume by 90% over the previously allowable volume and will affect about half the wells. For those who own these wells, life has indeed become more complicated and less profitable.
The other concern is RRC’s targeting SWD as the cause of this seismicity. To be fair, the RRC did not definitively claim that SWD is responsible, and the announced restrictions clearly state that this will be a year-long trial to see if seismicity reduces under the restrictions. Give the
RRC credit, it had the courage to perform a field-wide experiment.
The E&D article shows data that suggest there are no direct correlations between SWD and seismicity in the Gardendale SRA. Tectonics appear to result from a complicated dance between fluid extraction, injection, and fracturing. This is not a bold statement; why wouldn’t the earth violently respond to all this sudden mass and pressure redistribution? I do not expect to see much if any difference in seismicity after the year-long restriction expires, and I expect allowable injection volumes will reset to previous levels. But what I think is irrelevant, and we will have an opportunity to see for ourselves.
Regardless of the outcome, the truth is that the Permian basin is really a vast water field that produces oil as a byproduct, and the produced water not only needs to be dealt with in the present, but plans need to be made to deal with even more in the future. Injection may be naturally limited. Injection pressures at the surface are approaching maximum allowable levels, and without monitoring bottomhole pressures, who knows what is really going on down there?
Fortunately, Texas created the Texas Produced Water Consortium specifically to address these issues. The bill creating it was signed into law in June of this year and the consortium’s mission is to study both the economic impact of resuing produced water and the technology needed to reuse it. In addition to monitoring seismicity and following the trail of produced water from wellhead to disposal, it will follow New Mexico’s Produced Water Consortium studies of alternative uses for produced water, from irrigation to industrial plant cooling.
In the meantime, the good people of West Texas may have to take tips from California on how to earthquake proof their houses.
