Does saltwater disposal cause earthquakes?

.Underground Injection Issues - Seismicity                                    December 21, 2012
The Saltwater Disposal Institute (SWDI) specializes in economical, safe management of Oil and Gas wastes, primarily waste water and primarily via deep-well injection. We will publish this blog on a regular basis to shed light on regulatory trends and industry responses for the benefit of general public and industry investors.

Deep-well injection in the news:
Injection wells, especially those associated with the Shale-Gas play; appear every day in the national news media. Conflicting stories often appear side-by-side in print, internet, and on broadcast news. Well owners and investors must be aware of potential environmental liabilities associated with disposal wells and earthquakes. Several well-known and researched seismic events form the nugget of these news stories; summaries are provided below:

Photo: Amy Sancetta, A.P. With the skyline of Youngstown in the distance, a brine injection well owned by Northstar Disposal Services, LLC works. The company has halted operations at the well, which disposes of brine used in gas and oil drilling, after a series of earthquakes hit the Youngstown area.  Source: Aaron Marshall, Cleveland Plain Dealer, Jan 15, 2012.

Ohio:  Columbia University seismologist John Armbruster reports his evidence and conclusion (http://www.cleveland.com/open/index.ssf/2012/01/earthquake_raises_issues_on_oi.html) that the deep disposal of thousands of barrels of brine wastewater daily into the Youngstown, Ohio injection well caused the earthquakes including the widely publicized 4.0 quake on New Year's Eve 2011.

Armbruster located the epicenter within a mile of the Northstar Disposal Well at approximately 7,500 feet deep.  The disposal wells adjacent to the epicenter manage large volumes of water originating in the shale-gas play; it injects waste water as deep as 9,180 feet.  The Ohio Department of Natural Resources has shut down four disposal wells in the area.

Arkansas: North Central Arkansas has lately seen a number of unusual quakes that have made the news.  The Guy-Greenbrier swarm culminated in a 4.7 quake on February 27, 2011.  The quakes had depths measured between 3.9 and 2.4 miles (12,000 to 20,000 feet). (http://deathby1000papercuts.com/2011/04/new-earthquake-swarm-in-arkansas-april-8-2011-dozen-small-to-moderate-quakes-rattle-greenbrier/ )  The Arkansas Oil and Gas Commission has ordered injection wells in that part of the state to be shut-in until further decisions can be made.     

Texas: The Dallas-Fort Worth area has been the location of recent noticeable earthquakes.  Frohlich et al,    (http://startelegram.typepad.com/files/earthquake-study-10march2010.pdf ) map locations of natural and induced quakes around DFW and relate several to SWDs.  In 2008 and 2009 several clusters of quakes occurred with strengths of 1.5 to 3.3 Richter, correlated in location and depth to large oil and gas disposal wells in the area of Cleburne, Texas. The wells have been voluntarily shut-in by their operators. Depths of the quakes match up well to the Ellenburger injection zone. The map produced by Frohlich et al illustrates the phenomenon - while many Barnett shale-gas wells operate in the area of the quakes, two large disposal wells are also located in the area and only one disposal well is closely correlated to recent seismic activity. At the same time, quakes extend less than a mile from that particular disposal well. This is clear evidence that it is the disposal well, not the shale-gas wells that have initiated these particular quakes.

Colorado: In 1967 a 5.5 magnitude earthquake shook the area of Colorado around the Rocky Mountain Arsenal where a very large, 12,180-foot deep disposal well was injecting large volumes of hazardous wastes (that is, not associated in any way with oil and gas activity).   (http://foodfreedom.files.wordpress.com/2011/11/earthquake-hazard-associated-with-deep-well-injection-report-to-epa-nicholson-wesson-1990.pdf)  The quake detectors located the epicenter of the larger quakes at the base of the injection zone in the deep well.  The USGS and the EPA were convinced of a causal relationship and the well was shut-in, although the strongest quakes occurred after the shut-in. 

Oklahoma: On November 2011 several earthquakes occurred in Central Oklahoma. The swarm of events culminated with a November 5^th 5.6 magnitude temblor that was noticeable over a large portion of the state. The quakes were centered around Lincoln County.  Dr. Katie Keranen of the University of Oklahoma presented a paper at the American Geophysical Union conference this month entitled Fluid injection triggering of 2011 earthquake sequence in Oklahoma, here is the abstract of that paper:

Significant earthquakes are increasingly occurring within the United States midcontinent, with nine having moment-magnitude (Mw) ≥4.0 and five with Mw≥5.0 in 2011 alone. In parallel, wastewater injection into deep sedimentary formations has increased as unconventional oil and gas resources are developed. Injected fluids may lower normal stress on existing fault planes, and the correlation between injection wells and earthquake locations led to speculation that many 2011 earthquakes were triggered by injection. The largest earthquake potentially related to injection (Mw5.7) struck in November 2011 in central Oklahoma. Here we use aftershocks to document the fault patterns responsible for the M5.7 earthquake and a prolific sequence of related events, and use the timing and spatial correlation of the earthquakes with injection wells and subsurface structures to show that the earthquakes were likely triggered by fluid injection. The aftershock sequence details rupture along three distinct fault planes, the first of which reaches within 250 meters of active injection wells and within 1 km of the surface. This earthquake sequence began where fluids are injected at low pressure into a depleted oil reservoir bound by faults that effectively seal fluid flow. Injection into sealed compartments allows reservoir pressure to increase gradually over time, suggesting that reservoir volume, in this case, controls the triggering timescale. This process allows multi-year lags between the commencement of fluid injection and triggered earthquakes.

This paper will be used by critics of deep-well disposal to oppose new and existing permits for commercial disposal wells. Operators and investors need to be aware of this information – it may be possible that large disposal projects can cause significant earthquakes.

Colorado: The August 23, 2011 quake outside of Trinidad Colorado was described by the USGS as a 5.3 magnitude quake originating from a point 2.5 miles below the surface. Author Art McGarr of the USGS and colleagues totaled earthquakes in the Raton Basin and noted a total of five quakes 3.0 and larger from 1970 to 2001 and 95 quakes 3.0 or higher from 2001 to 2011; the annual rate for these two periods therefore increased more than 50 times from 0.167 per year to 9.5 per year. The USGS study – Present Triggered Seismicity Sequence in the Raton Basin of Southern Colorado/Northern New Mexico – was presented in San Francisco at the American Geophysical Union annual conference on Dec 5, 2012. Following is the abstract:

The occurrence of an earthquake of magnitude (M) 5.3 near Trinidad, CO, on 23 August 2011 renewed interest in the possibility that an earthquake sequence in this region that began in August 2001 is the result of industrial activities. Our investigation of this seismicity, in the Raton Basin of northern New Mexico and southern Colorado, led us to conclude that the majority, if not all of the earthquakes since August 2001 have been triggered by the deep injection of wastewater related to the production of natural gas from the coal-bed methane field here. The evidence that this earthquake sequence was triggered by wastewater injection is threefold. First, there was a marked increase in seismicity shortly after major fluid injection began in the Raton Basin. From 1970 through July of 2001, there were five earthquakes of magnitude 3 and larger located in the Raton Basin. In the subsequent 10 years from August of 2001 through the end of 2011, there were 95 earthquakes of magnitude 3 and larger. The statistical likelihood of this rate increase occurring naturally was determined to be 0.01%. Second, the vast majority of the seismicity is located close (within 5km) to active disposal wells in this region. Additionally, this seismicity is primarily shallow, ranging in depth between 2 and 8 km, with the shallowest seismicity occurring within 500 m depth of the injection intervals. Finally, these wells have injected exceptionally high volumes of wastewater. The 23 August 2011 M5.3 earthquake, located adjacent to two high-volume disposal wells, is the largest earthquake to date for which there is compelling evidence of triggering by fluid injection activities; indeed, these two nearly-co-located wells injected about 4.9 million cubic meters of wastewater during the period leading up to the M5.3 earthquake, more than 7 times as much as the disposal well at the Rocky Mountain Arsenal that caused damaging earthquakes in the Denver, CO, region in the 1960s. Much of the seismicity since 2001 falls on a 15km-long, NE-trending lineation of seismicity dipping steeply to the SE. The focal mechanisms of the largest earthquakes since mid-2001 are consistent with both the direction of the seismicity lineation and the regional tectonic regime of east-west extension centered on the Rio Grande rift.

While a cause-and-effect relationship has not been demonstrated as yet for the Trinidad quakes, the circumstantial evidence is persuasive. Deep well injection apparently does induce this seismicity. Many of the quakes have been minor but a 5.3 magnitude is certainly large enough to damage local structures.

Dr. McGarr also presented a compilation of nine injection – earthquake pairs across the continent.  Included is a plot of magnitude versus injection volume.  This plot could be used as an approximation of maximum injection volume that can be allowed before reaching a maximum allowable earthquake.  For example, if the agency decrees that induced earthquakes can be no more than 3.0 magnitude (approximately the smallest event detected by people in the open), then an individual injection well could only inject a total volume of 7,500 bbls (1,200 m³). 

The methodology used by Dr. McGarr should be utilized to zero in on a more accurate determination for the safe injection limit that could then be incorporated into state and federal regulations. While there are geological factors that might affect induced seismicity (such as proximity to faults, brittleness, etc.), these factors are poorly known in most areas and around most SWD wells. The best solution to defining an injection limit is to plot as many SWDs from varied settings to arrive at a single, conservative limit that may be scientifically applied to all geological settings. Whatever the methodology, more data is required.

Advice to SWD owners and investors: Disposal wells are most often drilled in areas of good subsurface control and good geological knowledge.  In most cases seismic information should exist to predict the presence of large faults at depths similar to the injection zones.  It would certainly behoove the owner-operator of the disposal well to include documentation of faulting in the area with the disposal well permit application. Going further, it would be valuable to install seismic monitoring devices near the SWD well, interpretation of the monitoring records could be performed by the operator, the regulatory agency, or research academics interested in the field. It is up to the operator to determine the cost:benefit calculation for installing earthquake monitors.

About the author:  Bruce G. Langhus, Ph.D. is a petroleum geologist with over 45 years' experience in oil and gas business including water-flood design and operation; Class I, II, and III disposal well location, permitting and operation; and injection well remediation.  Dr. Langhus has been the Class II Program Manager in Oklahoma, the second largest UIC program in the country.  He was a founding partner of ALL Consulting, a successful geotechnical consultancy in Tulsa, OK.  Dr. Langhus is now part of Amerex Resources, operators of disposal facilities in Texas, Oklahoma, Montana, and North Dakota.