Less than 1% of wastewater disposal wells in the United States used by the oil and gas industry have a potential link to induced seismicity, according to a report released this month by Energy In Depth (EID), an energy industry-backed national shale gas education initiative.
Meanwhile, a 4.7-magnitude earthquake struck northern Oklahoma early Thursday, and was felt across large swaths of the state and neighboring Kansas. In response to the quake, the Oklahoma Corporation Commission's (OCC) Oil and Gas Conservation Division (OGCD) ordered two disposal wells to stop operations immediately, and for another 23 wells to reduce their intake volumes.
According to a 21-page report by EID, the U.S. Geological Survey (USGS) says there are about 150,000 Class II injection wells across the country with activities linked to the oil and gas industry. Of those 150,000 wells, about 40,000 are designated as disposal wells. EID said data from USGS and several peer-reviewed studies show that of the 40,000, only 218 wells either have a link, or are suspected of having a link, to induced seismicity.
"In other words, only 0.15% of all Class II injection wells, and 0.55% of all federally regulated disposal wells in the United States, have been tangentially associated with a seismic event of any size," EID said. "This means that 99.85% of all Class II wells in the United States, and 98.45% of all disposal wells in the United States, continue to operate without any issues whatsoever related to seismicity."
EID said 89 of the 218 wells with potential links to seismicity are in Oklahoma and 81 are in Kansas, which means that combined the two states account for 78% of the wells under scrutiny. The remaining wells are in Texas (27), Colorado (11), Arkansas (four), New Mexico (three), Alabama (two) and Ohio (one).
Although Oklahoma had endured the most seismic activity, EID said wastewater volumes in the state were about 30% higher in the 1980s, yet there were only a handful of earthquakes reported at that time. EID also said that while 99% of all earthquakes in Oklahoma are within nine miles of an injection well, several parts of the state -- specifically, southwestern, western and northeast Oklahoma -- have many injection wells but either little or no seismic activity.
"Data [from the 1980s] are sparse, and some scientists have suggested that much of the water may have been injected into wells used for enhanced oil recovery," EID said. "Regardless, this underscores the fact that any link between wastewater injection and seismicity is highly complex, and due to a variety of factors that are often site-specific."
EID cited a 2014 study by researchers from Cornell University, the University of Colorado, Columbia University and the USGS that said four wells may have caused up to 20% of the earthquakes between 2008 and 2013 in the central United States, including Oklahoma (see Shale Daily, July 7, 2014).
The USGS's Earthquake Hazards Program said the epicenter of Thursday's earthquake was eight miles southwest of Cherokee, OK, at a depth of 3.8 miles. A map on the program's website indicates the temblor was felt within a 100-mile radius of Cherokee.
On Thursday, the OCC ordered Aexco Petroleum Inc. to shut down its McDaniel SWD 1-18 well, and for Chesapeake Operating Inc. to do likewise with its Dutch Harbor SWD 1-14 well. Both wells are located within three miles of the epicenter of Thursday's earthquake. The other 23 wells were order to reduce their volumes by either 25% or 50%. Total daily average intake is to be reduced by 40%, from 209,600 b/d* to 126.465 b/d*.
For months, the OCC has been taking action to reduce the number and intensity of earthquakes in the state, ordering some disposal wells to shut down operations and others to reduce the volume of wastewater they accept. The watershed moment came in April, when the OGCD issued new rules for injection well operators working in "areas of interest" that inject into the Arbuckle Formation, the state's deepest formation (see Shale Daily, April 2).
The OCC shut down two wells and ordered volumes to be cut at another three in September (see Shale Daily, Sept. 21), and ordered 13 wells to change operations in October (see Shale Daily, Oct. 19). The operators of two wells voluntarily agreed to shut down their operations in July, and a third agreed to cut intake volumes by half (see Shale Daily, July 29).
Last March, the OGCD issued a directive to operators of 347 disposal wells targeting the Arbuckle formation to prove that they are not injecting oil and gas waste into basement rock below it. The directive was expanded to include an additional 211 disposal wells earlier this month. The wells are all within "areas of interest," which include 21 of the state's 77 counties that have seen increased seismicity (see Shale Daily, July 20; April 2).
Scientists with the Oklahoma Geological Survey (OGS) reported in April that the state was being hit by earthquakes at a rate about 600 times greater than historic background data (see Shale Daily, April 22). Seismicity increased from an average of one-and-a-half earthquakes of 3.0 magnitude or greater to about two-and-a-half such earthquakes every day in 2014.
According to the OGS, the earthquakes are primarily occurring within the crystalline basement. The majority of the state's approximately 900 injection wells target the Arbuckle formation, which closely overlies the crystalline basement.
Last fall, Oklahoma regulators shut in a disposal well that was thought to have been drilled too deep following a spate of seismic activity in the area (see Shale Daily, Oct. 31, 2014).
*Correction: In the original article, the Oklahoma Corporation Commission's Oil and Gas Conservation Division provided inaccurate data for the total daily average and reduced daily average of 25 wastewater wells involved in an order on Thursday. The correct figures are 209,600 b/d for the total daily average, and 126,465 b/d for the reduced daily average.