seismic monitoring & mitigation - OERB

Environmental Stewardship | Land

SEISMIC MONITORING & MITIGATION

There have been questions raised about the increase in seismic activity in Oklahoma over the past five years. Like the citizens of the state, Oklahoma’s oil and natural gas producers are concerned about these events and are helping seismologists and other experts gain insights regarding the nature of these events. Oklahoma’s oil and natural gas producers are working closely with the Oklahoma Geological Survey, the University of Oklahoma College of Earth and Energy and the Oklahoma Corporation Commission to better understand current seismic activity in our state.

OKLAHOMA’S SEISMIC HISTORY Oklahoma has long been recognized as having earthquake activity as it sits on top of numerous and sizable natural fault lines. In fact, Oklahoma has been seismically active for over a millennia. Our state has several major geological-paleo structures like the Nemaha Ridge, the Arbuckle Mountains and the Wichita Mountains. These notable geological features are the results of long occurring and intensive seismic activity.

Since the Oklahoma Geological Survey began monitoring seismic activity in the 1970s, there has been at least one documented earthquake in 72 of Oklahoma’s 77 counties.1 While 90 percent of earthquakes occurring in Oklahoma are too small to be felt, they are recorded and reported by the Oklahoma Geological Survey.1

UNDERSTANDING EARTHQUAKES AND SEISMICITY Seismicity refers to the earthquake activity of a given area, i.e. the frequency and magnitude of seismic events. Induced seismicity is usually understood as micro seismicity, which results from human activity that typically occurs with large scale construction or engineering projects that require digging into extreme depths in the earth’s surface.3 These activities involve changes in stress, pore pressure, volume and load in underground rock formations.3 Physically there is no difference between induced and natural seismicity. One major difference between naturally occurring and induced seismicity is that the vast majority of induced seismic events are of a small magnitude, usually below zero. Events that fall below zero magnitude cannot be felt at the earth’s surface. In almost all cases the magnitude of induced seismicity is less than the largest naturally occurring earthquake in the same area.3

Arbuckle Mountains, Turner Falls Park, Oklahoma

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SEISMIC MONITORING & MITIGATION It is incredibly difficult to know whether a given seismic event is naturally occuring or induced. Scientific rules and measures to decipher whether an earthquake is induced or natural are not yet well established or accepted by the scientific community.

SEISMIC RESEARCH TO DATE Based on the Oklahoma Geological Survey research to date, the overwhelming majority of Oklahoma earthquakes appear to be the result of naturally occurring stresses that are consistent with the regional Oklahoma fault field.1 The majority of the historical and more recent earthquakes are located on, or near, the Nemaha Ridge and the Ouachita-Arbuckle-Wichita mountain front, which are major geological-paleo structures. The OGS has not ruled out that some seismic activity may have a relation to water disposal/injection wells, but the majority of this activity is not strong enough to be felt at the earth’s surface. Further, the energy released by earthquakes is thousands of times greater than the energy that has been required for water injections/disposal, which demonstrates that the earthquakes themselves are ultimately, the release of natural faults.1 Disposal wells have been used for decades in Oklahoma and are overseen by state and federal agencies like the Environmental Protection Agency, the Oklahoma Corporation Commission and the Oklahoma Department of Environmental Quality. There are more than 4,000 of these Class II disposal wells currently permitted throughout Oklahoma. Because oil and natural gas is produced in 70 of Oklahoma’s 77 counties, any seismic activity is likely to occur near oil and natural gas activity.1 For this reason, more scientific knowledge than the correlation of time and space is necessary to document any induced seismicity and will continue to be studied by the OGS.1 Regarding the possible relationship between earthquakes and hydraulic fracturing, the following observations have been made to date: Hydraulic Fracturing is frequently accompanied by microseisms that are recorded with sensitive listening

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devices and analyzed with scientific measures about the magnitude of seismic activity related to the process of hydraulic fracturing. A review of published research shows no cases of injuries or damage as a result of the very low level of seismic activity related to hydraulic fracturing in more than one million applications. One study monitored several thousand shale fracture treatments in various North American shale basins. The largest microseism recorded in that study has a measured magnitude of 0.8 on the Richter scale. That magnitude would never be felt at the earth’s surface and can only be detected with highly sensitive seismic monitoring tools.

OKLAHOMA FAULT MAP While Oklahoma has several well known and documented fault lines, due to its complex geographical history, there are many undocumented faults throughout Oklahoma. The Oklahoma Geological Survey is working closely with Oklahoma’s oil and natural gas industry and other scientists on developing a new fault map for the state. The map above shows the faults documented to date throughout the state of Oklahoma. Map courtesy of Oklahoma Geological Survey. June 2014.

“The process of hydraulic fracturing a well as presently implemented for shale gas recovery does not pose a high risk for inducing felt seismic events ... only a small fraction of injection and extraction activities among the hundreds of thousands of energy development sites in the United States have induced seismicity at levels noticeable to the public.” –N ational Research Council. Induced Seismicity Potential in Energy Technologies . Washington, DC: The National Academies Press, 2013.


SEISMIC MONITORING & MITIGATION

ONGOING SEISMIC RESEARCH Numerous studies to date are inconclusive as to the degree of inducement from water injection wells and more independent studies are ongoing. Many Oklahoma operators currently map active and inactive fault lines within a certain radius of their activities and report these faults to the Oklahoma Geological Survey. The Oklahoma Geological Survey, in cooperation with faculty from the University of Oklahoma, the Oklahoma Corporation Commission and the Office of the Oklahoma Secretary of Energy and Environment recently received a grant from the Research Partnership to Secure Energy for America. This grant will help the OGS to increase monitoring of seismic activity and will result in increased detection of not-felt events. In coordination with the OGS and Oklahoma Corporation

AN ESTIMATED

$455 MILLION AND 19,527 MILES

OF FAULT DATA HAS BEEN REPORTED TO THE

OKLAHOMA GEOLOGICAL SURVEY TO DATE. Commission, many oil and gas producers are monitoring seismicity and reporting all activities and discovered faults. These collaborative efforts among researchers, federal, state and local governments and the energy industry will result in better understanding seismic risk in Oklahoma.

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Oklahoma Geological Survey, Position Statement – Oklahoma Earthquake Activity, February 2014

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United States Geological Survey, The Science of Earthquakes, 2014

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Lawrence Berkley National Laboratory, Earth Sciences Division, Induced Seismicity Overview, 2014.

LEARN MORE To learn more about seismic activity in Oklahoma, please visit the following sources: Oklahoma Geological Survey Earthquake Fact Sheet http://www.ogs.ou.edu/pdf/OGS_POSITION_STATEMENT_2_18_14.pdf National Research Council. Induced Seismicity Potential in Energy Technologies. Washington, DC: The National Academies Press, 2013. http://www.nap.edu/catalog.php?record_id=13355 National Academies Press. Steps towards Seismic Best Practices Protocol http://www.nap.edu/openbook.php?record_id=13355&page=151 Unconventional Oil and Gas Report. Understanding the Science Behind Induced Seismicity. October 2013 http://www.ogj.com/articles/uogr/print/volume-1/issue-3/understanding-the-science-behind-induced-seismicity.html http://www.api.org/~/media/Files/Policy/Hydraulic_Fracturing/Facts-HF-and-Seismic-Activity.pdf Ground Water Protection Council. A White Paper Summarizing a Special Session on Induced Seismicity http://www.gwpc.org/events/gwpc-proceedings/2013-uic-conference

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