Friday, December 30, 2016

No proven tie between quake, 
injection wells ?

State oil and gas regulators are in monitoring mode following a minor Christmas Day earthquake west of New Castle, but have found no obvious connection between the quake and wastewater injection wells in the area.
Stuart Ellsworth, engineering manager for the agency, says it also has done an evaluation following a larger, magnitude-4 earthquake that happened Dec. 23 in northern New Mexico, just across the border from Trinidad, Colo. But it found that the few Colorado injection wells near that epicenter are relatively inactive, either being shut in or having fluids injected at a low rate.
The quake around 11:15 p.m. Christmas night was a magnitude 2.9 with an epicenter just south of the Colorado River. On Oct. 23 another, an even smaller quake of a magnitude 2.1 occurred almost immediately north of the Dec. 25 epicenter, just across the river and Interstate 70.
Ellsworth said four companies are operating injection wells within about 6 miles of the site of the Christmas Day quake, mostly to the southwest. All are injecting wastewater at low volumes and within specified pressures, he said. Higher injection volume rates and pressures are considered factors that could contribute to earthquakes.
Scientists and Oklahoma’s state government have determined there’s an apparent correlation between oil and gas wastewater wells and a sharp increase in earthquakes in that state. And an injection well in the Greeley area was linked a few years ago to a 3.2-magnitude quake and smaller subsequent ones.
Ellsworth said Colorado has about 350 wastewater disposal wells, compared to about 3,000 in Oklahoma. Wells in Oklahoma are undergoing injection rates of about 30,000 to 60,000 barrels of water a day, and the Greeley well had an injection rate of 10,000 barrels a day. Ellsworth said most wells in Colorado see injection rates of about 1,000 barrels a day. He said rock formations can’t absorb water being injected into them at too fast of a rate, and the science suggests against exceeding 10,000 barrels a day.
The COGCC has instituted a system for responding to earthquakes in areas where there are injection wells, with criteria for moderating or suspending operations in the case of higher-magnitude quakes. The system calls for monitoring an area in the case of an earthquake of magnitude 2.5 or higher, and so the agency is monitoring the area of the Christmas quake, Ellsworth said.
Ellsworth said the COGCC hasn’t requested any injection-operation changes by companies in the case of either the Garfield County or New Mexico border quakes.
Don Blakeman, a geophysicist and earthquake analyst with the U.S. Geological Survey, noted that earthquakes aren’t uncommon in Colorado.
“We see them every once in a while. They’re not unusual at all,” Blakeman said.
Ellsworth said there were two quakes in that same area west of New Castle back in the 1990s. That was before there was much drilling and injection well activity in that area. He said there haven’t been a lot of earthquakes in western Colorado’s Piceance Basin despite it being peppered with injection wells, and there’s never been a correlation between injection wells and earthquakes in the basin.
Decades ago in the Rangely area, federal researchers affirmed the ability to inject fluids to the point of causing seismic activity by doing just that, Ellsworth said.
While some researchers have suggested a link between high-rate injection wells and earthquakes in the Trinidad area, Ellsworth said the COGCC has never been able to make a correlation between injection activities and quakes there. Part of the problem in trying to draw such conclusions in that area is that it has a long history of natural-occurring earthquakes.
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