On June 24, the Colorado Oil and Gas Conservation Commission ordered NGL Water Solutions DJ LLC to halt activity for 20 days at one of its wastewater injection sites in Weld County, following a magnitude 2.6 earthquake recorded June 23.The site, called SWD C4A, is east of the Greeley-Weld County Airport.According to a National Public Radio post at http://stateimpact.npr.org, an injection well is an underground site, which stores fluids relating to oil and gas drilling, including fluids used for hydraulic fracturing.The company agreed to the stoppage to gather necessary data and further analyze whether the injection activity at that site was tied to the recent earthquake in the vicinity, said Matt Lepore, COGCC director. The COGCC will also use data gathered from a 3.4 magnitude earthquake that occurred in Greeley May 31.The University of Colorado at Boulder conducted seismic monitoring and continued throughout the 20-day shutdown period, Lepore said. ìWe havenít definitively concluded that the well caused the seismic events,î he said. ìSome (seismic) events had been occurring during the shutdown period, and weíre not sure if those were connected to the well. Thatís something weíre still grappling with.îDuring the shutdown, NGL inspected the well and noticed a possible cause, Lepore said. ìWe did flow tests during the shutdown period, and they demonstrated that a high percentage of water was going in at the bottom of the well; and the logs showed a potentially highly fractured part of the well,î he said. To battle the fracture, the operator clogged about 400 feet of the bottom portion of the well with cement. Tests now indicate that a much smaller percentage of the water is going into that area, he said.On July 18, NGL was given the go-ahead to begin injecting wastewater back into the well at a reduced volume flow of 5,000 barrels of water per day, which is significantly less than the previous volume flow, Lepore said.Monitoring will continue for 40 days after that, with assessments at day 20 and then at day 40 to determine how to proceed, he said. If at day 20 there are no seismic events greater than 2.5 on the Richter scale, NGL will be allowed to increase the flow from 5,000 barrels per day at a maximum pressure of 1,512 pounds per square inch to 7,000 per day at the same pressure, Lepore said. If another event occurs that is higher than a magnitude 2.5 ó which represents the U.S. Geological Surveyís default threshold for seismic event ó within a 2.5 mile radius of the well, the COGCC will immediately halt activity at the site again, Lepore said.ìWeíre moving slowly and deliberately and just taking it one step at a time,î Lepore said.Other areas around the country like Oklahoma have experienced similar seismic activity linked to wastewater injection sites, according to an article published on colorado.edu July 3 by CU-Boulder: ìPrior to 2008, Oklahoma averaged about two earthquakes per year with a magnitude of 3.0 or greater, according to the U.S. Geological Survey. This year, between Jan. 1 and May 2, there have been 145 Ö . The increase in earthquakes in the state coincided with a boom in hydraulic fracturing, which generates a large amount of wastewater.îThe article further states, ìThe researchers used hydrogeological models to determine how much pressure the injected wastewater was building up in the pores of the rocks underground. Under high pressure, fluids can seep into existing faults and pry apart the rocks, allowing them to slip past each other more easily and cause earthquakes.îAccording to an article posted on KOCO5 News Live koco.com July 23, Glen Brown, a geologist with Continental Resources, addressed fellow geologists at a luncheon in Oklahoma City, hosted by the Oklahoma City Geologist Society. Brown said he believes the surge in earthquakes in the state is related to a worldwide surge in seismic activity, including recent massive earthquakes in Japan and Chile, rather than being induced by wastewater injection wells.Brown said the amount of seismic activity in the last few years is unusual, but itís not unprecedented. What is unprecedented is the increased ability to observe and measure the earthquakes, he said.Shemin Ge, professor of hydrogeology at CU-Boulder, said the injection site in Weld County has not been operating as long as the sites in Oklahoma that appear to have caused those earthquakes. Thus, in terms of total volume, there isnít as much liquid to create the pressure that could lead to seismic activity, she said.ìThe response from the Colorado Oil and Gas Conservation Commission was pretty quick, and I think thatís a good thing to prevent or mitigate any potential hazard,î she said. ìHowever, I would have a hard time not to relate the (seismic) activity in Oklahoma to those injection sites. That area was pretty quiet in general before all these activities. Itís not like Japan or California that see a lot of activity. We have a very good reason to suspect that those earthquakes (Oklahoma) are related to injection activities.îAs for the injection site in Weld County, the COGCC is still investigating whether NGL is in violation of the permitted injection volumes, Lepore said. If the company is in violation, they could face financial penalties, he said.
