As oil drilling in Kansas has slowed since winter, so have the number and power of earthquakes emanating from Harper and Sumner counties.
It’s no coincidence, say state geologists.
There were 67 earthquakes with a magnitude of at least 3.0 in the last year, including a 4.9 quake in November, according to the U.S. Geological Survey. Since April 1, there have been just 15 — and none in July.
But the geologists remain cautious. They don’t know yet how much of the decline in earthquakes is caused by a slowdown in the use of disposal wells for the waste saltwater created as a byproduct of oil and gas drilling.
The update on the state’s study of injection-well-related earthquakes was delivered by a panel of state geologists and regulators at the Kansas Independent Oil and Gas Association annual meeting Monday.
It’s too early to start issuing rules on how drillers must operate, said Rex Buchanan, interim head of the Kansas Geological Survey and one of the speakers on the panel.
Oil drilling has fallen sharply since January because of falling oil prices. Then in March, the Kansas Corporation Commission ordered a reduction in the amount of saltwater pumped down about 20 injection wells in five areas of Harper and Sumner counties that have seen heavy seismic activity.
What makes it complicated is that Kansas oil and gas drillers have been fracking wells and pumping saltwater into disposal wells for more than 60 years all across the state with relatively little seismic activity. So the oil and gas industries were pretty skeptical when people first started to connect the two.
The injection wells are drilled down to the Arbuckle formation, a porous layer of sedimentary rock that sits many thousands of feet down just above the “basement” layers of much-harder igneous and metamorphic rock. The saltwater for decades has been easily absorbed into the Arbuckle, so what’s different now?
The volume, said the geologists on Monday.
The arrival of large-scale horizontal drilling and multistage fracking of the Mississippian Lime starting in 2010 produced huge quantities of subsurface water, an average of 15 barrels of saltwater for every barrel of oil, said Lynn Watney, a geologist with the Kansas Geological Survey. In 2014, he said, oil and gas drillers pumped 90 million barrels of water into the Arbuckle in Harper County.
That’s what the geologists don’t quite understand. They can’t pinpoint one earthquake as being caused by one well.
It seems to be more of a large-scale pressure generated by multiple wells on often unmapped faults. That makes it difficult to define where it’s OK to inject water and where it isn’t.
They want to know as exactly as possible what’s going on, why and under what conditions before issuing any orders to drillers.
Buchanan said it’s important to keep studying the problem because the price of oil will go back up and drillers will start getting busy again.
“What you don’t want is to be back in the same spot five years from now,” he said.