by Mark Christian - January 20, 2018 - Updated 8:01 pm CDT
Author's note: It is helpful for readers to understand wastewater disposal when reading the recently published study by Virginia Tech researchers. To enhance that understanding, I included a couple of paragraphs about wastewater disposal via underground injection in Oklahoma.
Since 2011, Oklahoma became the most earthquake-prone state in the nation. Over the same time period, the volume of wastewater pumped into the Arbuckle formation via wastewater disposal wells increased 81%, a fact that plays a leading role in the scientific community's hypothesis that wastewater disposal wells induce seismic activity.
Most people think about oil production as pure crude oil flowing up and out of the ground. In reality, a typical oil well produces a brownish mixture of oil, natural gas, and produced water, along with dissolved solids from the ancient reservoir. The mixture is produced through the wellhead and flowed to a separator located at the wellsite to separate the water from the gas and oil.
After the produced water has been through the separator and stripped of hydrocarbons, it is ready for disposal. The most common method of wastewater disposal in Oklahoma is injection into underground disposal wells. Since water recycling technologies are currently not in widespread use due to the cost, most oil companies turn to underground injection as their most cost-effective disposal option.
Disposal wells are drilled deep to get below the water table and other productive oil and gas formations. There are several deep rock layers suitable for produced water injection, but in Oklahoma, the "Arbuckle formation" is the most popular choice. Oil companies have completed more than 60% of Oklahoma disposal wells to the Arbuckle formation - an underpressured sedimentary rock formation that lies just above the crystalline basement rock (granite).
The lifespan of a typical oil or gas well in Oklahoma can exceed fifty (50) years. Hydrocarbon production gradually declines over time, but the well will continue to produce formation water. A single well can produce tens of millions of barrels of salt water over its lifetime. Usually, when a well goes "dry", meaning hydrocarbon production has stopped, water production continues.
In 2015, produced water injection in Oklahoma peaked at 1.5 billion barrels. That's equivalent to 63 billion gallons.
For several years in a row, the Mississippi Lime play in Northern Oklahoma experienced the largest year over year increase in produced water injection. The largest growth occurred in Alfalfa and Woods County. Between the two counties, disposal volumes exceeded 42 million gallons per day until seismic activity caused disposal well shutdowns and volume curtailments.
Although earthquake activity began to pick up in 2009, the general public did not take notice until 2011. There was little data on induced seismicity available to the Oklahoma scientific community, but strong earthquakes shook homes on a daily basis and kept citizens focused on the issue.
In May of 2014, the USGS and the Oklahoma Geological Survey sounded a rare alarm. They issued an earthquake warning for the first time in any state east of the Rockies. The agencies warned that the risk of a damaging earthquake (larger than magnitude 5.0) had increased significantly in central Oklahoma where Oklahoma City is located along with the bulk of the population.
In 2015, both the State's Governor, Mary Fallin (R), and Oklahoma's largest oil and gas trade association, the Oklahoma Independent Petroleum Association (OIPA), acknowledged a link between wastewater injection in the Arbuckle formation and the enormous number of earthquakes that rattled the state.
Virginia Tech study claims Okla. regulators aren't doing enough to stop earthquakes
The earthquake issue in Oklahoma has been the focus of numerous scientific studies from around the world. Last week, researchers at Virginia Tech's College of Science published a study that claimed Oklahoma authorities have not reduced wastewater disposal volumes enough to stop large earthquakes. The study also claimed that based upon a historical account of earthquake activity in the Sooner state, a salt water disposal well can trigger an earthquake 78 miles away, nearly four times the distance Oklahoma regulators currently believe injected wastewater can induce seismicity.
The study was led by Ryan M. Pollyea, an assistant professor with the Virginia Tech College of Science's geosciences department and director of the Computational Geofluids Laboratory. Pollyea conducted a geospatial analysis of earthquake activity in Oklahoma by plotting disposal well locations in relation to earthquake epicenters.
Pollyea's analysis indicated earthquake epicenters are tied in proximity and timeliness to wastewater injection and by tracking disposal well location data, the team could help predict how corresponding earthquake activity will change according to injection volume and time.
The correlation was clear: “When we plotted the average annual well locations and earthquake epicenters, they moved together in space,” says Pollyea. The researchers also found that SWD volume and earthquake occurrence are spatially correlated up to 125 km,(78 miles). That's the distance within which there seems to be a connection between injection volume, fluid movement, and earthquake occurrence. Virginia Tech News | January 10, 2018
Even more concerning, the Virginia Tech study says Oklahoma regulators have not reduced wastewater disposal volumes enough to stop the large, destructive earthquakes.
"When we compared the spatial correlation using datasets that include only magnitude 3-plus earthquakes, there was no change," said Pollyea, adding that a larger reduction in wastewater injection volumes is needed to reduce the dangers of large magnitude earthquakes. Virginia Tech News | January 10, 2018
Pollyea's study did not provide details on how much additional volume should be reduced nor did it take into account how substantially reducing or stopping injection can actually trigger an earthquake.
In a 2015 interview, former Oklahoma State seismologist, Austin Holland, discussed how a moratorium on wastewater injection could actually produce powerful earthquakes.
Putting a sudden stop to injections might actually cause new earthquakes. “There’s a fair amount of modeling that shows that might be the case,” he said. Austin Holland, Former Oklahoma State Seismologist | July 30, 2015
A Spanish research team studying the effects of post-injection seismicity found that after a formation is pressurized by long term water injection, a rapid decrease in formation pressure results in a rapid increase in stress on fault lines, further supporting Holland's view that stopping injection or reducing it too suddenly could destabilize existing fault lines and trigger earthquakes.
Specifically, post-injection seismicity may occur on unfavorably oriented faults that were originally stable. During injection, such faults become destabilized by thermal and shear slip stress changes, but are held static by the superposition of pressure forcing. However, they become unstable and fail when the pressure forcing dissipates shortly after injection stops abruptly, which suggests that the magnitude of post injection seisms can be lowered by reducing the flow rate slowly. Silvia De Simonea, Jesus Carreraa, Vıctor Vilarrasaa. Institute of Environmental Assessment and Water Research. Superposition approach to understanding triggering mechanisms of post injection seismicity. Barcelona, Spain. 2017.
Oklahoma Regulators Take Conservative, Data Driven Approach
Scientists working with the U.S. Geological Survey also believe that reducing injection volumes "too aggressively" may produce "unintended consequences".
In simple terms, wastewater injection causes pressure to build in rock formations over time. When injection stops abruptly or is reduced too quickly, the resulting loss of formation pressure can destabilize faults to a point of failure.
In past press releases and media interviews, the agency responsible for regulating Oklahoma's oil and gas industry (including underground injection), the Oklahoma Corporation Commission (OCC), stated they are acutely aware of these risks and use scientific data to calculate injection volume reductions and the rate at which the reduction is made.
Based on historical actions taken by the OCC, earthquakes are evaluated on a case by case basis and have been found to be, on average, 12 miles from the suspect disposal well.
After reviewing empirical data and consulting with state and federal geological surveys, university researchers, state seismologists, and oil industry geologists, the OCC developed a plan of action announced in a March 07, 2016 media release titled the "Regional Earthquake Response Plan for Central Oklahoma and Expansion of the Area of Interest" . The plan reduced disposal volumes by 40% and was a proactive step to mitigate future man-made earthquakes.
It defined a 15,000 square mile area of interest (AOI) which covers a large part of western and central Oklahoma. Additionally, it implemented an 11,000 square mile volume reduction for Arbuckle disposal wells located inside of the AOI and reduced injection volumes by 300,000 barrels per day.
In February of 2017, the OCC issued its latest proactive directive aimed at limiting growth of future disposal rates to ensure there are no surprise jumps in disposal volumes. The directive capped high volume disposal wells at a fraction of their permitted volumes which removed more than 2 million barrels per day of potential disposal capacity. The directive offers oil companies flexibility in how they handle their disposal, and OGCD Director, Tim Baker said, "the new rules were the result of a Data Driven approach".
OCC's efforts begin to pay off.
Since the regional volume reduction plan was implemented, earthquakes with magnitudes less than M3.0 have been significantly reduced on a year over year basis.
According to the U.S. Geological Survey, Oklahoma had 478 M3.1+ quakes in 2016. In 2017, that number dropped to 204, a decline of more than 50%.
Larger quakes still occur more frequently than the smaller quakes and scientists are trying to understand why? Some experts believe that falling reservoir pressures may be to blame.
The OCC and Oklahoma Geological Survey (OGS) are working together to better understand induced seismicity by studying reservoir characteristics in the Arbuckle formation and analyzing the precise relationships between volume, rate, timing of fluid injection, water movement along fault lines, and the effects of reservoir pressure over large areas.
The Virginia Tech study is helpful in terms of collecting new spatial data on Oklahoma's induced seismicity, but its recommendations implied that Oklahoma regulators and government officials are not doing enough, and that is not correct.
The OCC is making responsible and prudent decisions based upon scientific facts while collaborating with the Oklahoma Geological Survey, Oklahoma Department of Energy, oil companies, researchers at the University of Oklahoma and Oklahoma State University to better understand the Arbuckle formation and its characteristics.
Virginia Tech researchers analyzed the spatial correlation between earthquakes and the disposal wells believed to be responsible for inducing seismicity and concluded that a disposal well in Oklahoma can induce seismic activity up to 78 miles away. They did not examine local geologic features that prevent water movement over such long distances.
The 78-mile distance implies the OCC should draw larger circles around earthquake epicenters to capture more disposal wells in volume reductions zones. If the OCC were to execute this recommendation, nearly the entire state of Oklahoma would be inside of a volume restriction zone (including areas with no history of seismic activity). 95% of all disposal wells in Oklahoma, including every disposal well from Wichita, Kansas to Dallas, Texas would be included. See map below.
his would penalize oil companies by shutting down oil and gas production in areas where no seismic activity has occurred, costing hard working Oklahomans their jobs and creating an economic trickle down effect that would hurt the economies of local communities.
Oklahoma has become a laboratory for seismic research. Along with the USGS and Oklahoma Geological Survey, university researchers at Stanford, Cornell University, University of California, University of Colorado, University of Oklahoma, and even academic institutions in Europe have dedicated resources to better understand subsurface geology, underground injection, and water movement through formations under Oklahoma. The Oklahoma Corporation Commission is analyzing this research as it becomes available to enhance their existing knowledge.
None of that research has been critical of the OCC's efforts until the Virginia Tech research was published.
Critics of Oklahoma's efforts to eliminate induced seismicity should take a step back and consider all the variables at play, both above and below ground, instead of finding fault with a small piece of a big puzzle.
In the final analysis, earthquakes can bring down buildings and end lives. That is why our neighbors who work at the Oklahoma Corporation Commission are applying science and engaging expert partners to stop more earthquakes from occurring in Oklahoma.
And since our homes have stopped shaking three times a day, it looks like their efforts are beginning to pay off.
Article by Mark Christian, Senior Consultant at CHRIS Well Consulting, LLC.
© Mark Christian 2018. All Rights Reserved.
You may contact Mark at: email@example.com
Opinions expressed in this article are solely those of the Author and not those of CHRIS Well Consulting, LLC.
February 2016 - January 2018