LARAMIE WYOMING — The WSGS recently completed a study on the potential link between injection/disposal well activities by industry and earthquakes in Wyoming. After evaluating the entire state, six sites warranted further investigation; five of the sites showed no definitive link and one site (Site C) requires further study.

WSGS hazards geologists conducted the study based on reported earthquakes and injection/disposal well activities in Wyoming from 1984 to 2013. Using computer subsurface modeling software the geologists were able to map the wells operating during those years along with recorded earthquake events during the same time periods.

The Report Reads In Part:

Earthquake activity can be triggered by a number of sources. Volcanic activity, landslides, and movement along a fault are examples of natural causes of earthquakes. In rare instances, anthropogenic (human) influences can also cause an earthquake; these events are referred to as “induced seismicity.” Induced seismicity can potentially be triggered by a variety of industry related activities, including construction, geothermal energy production, mine subsidence and blasts, oil and gas field depletions, fluid injection for secondary and enhanced oil recovery, wastewater/fluid disposal, groundwater extraction, large water reservoir impoundment, drop forging, and military actions (conventional bombs and underground nuclear testing).

Given the recent national attention and focus on fracking in the United States, it is important to note that tens of thousands of wells have been fracked over the decades in Wyoming. To date the WSGS has observed no correlation between earthquakes and fracking operations. Some short-term micro-seismicity (below human detection) does occur in the Earth during a fracking operation, but does not represent what has become known as induced seismicity.

Induced seismicity generated by mining subsidence has been studied by industry and state and federal agencies. These events are often associated with mine workings and operations. Earthquakes generated from mine collapse range from magnitude 1.6 to 5.6 (Davies and others, 2013) with the vast majority occurring at the low end of the observed magnitude range. Examples of some of the relatively rare larger earthquakes related to mining in Wyoming include a 1995 partial ceiling collapse at the Solvay Chemicals trona mine in Wyoming that generated a 2 5.1 magnitude earthquake and a coal mine blast in 2012 at Cloud Peak Energy’s Cordero Rojo Mine that caused a magnitude 4.5 earthquake.

In cases of oil and gas field depletion, the flexure of overburden units generates shear stresses that, on rare occasions, can induce slip along a weak shale layer (Hamilton and others, 1992). At the Lacq natural gas field in southwest France, more than 1,640 earthquakes were detected ranging from magnitude 1.9 to 6.0 due to gas depletion (Bardainne and others, 2008).

It has also been recognized that fluid injection within the subsurface can occasionally generate earthquakes. One of the most notable induced seismic incidents in the Rocky Mountain Region happened in 1967, a magnitude 5.3 earthquake occurred near Denver, Colorado, as a result of military waste fluid that was injected into a deep borehole at the Rocky Mountain Arsenal, a U.S. chemical weapons manufacturing center (Hsieh and Bredehoeft, 1981). Once the cause of the earthquake was identified pumping ceased at the arsenal and the earthquakes subsided.

For many years fluids have been injected (secondary and enhanced oil recovery methods) into oil and natural gas fields to optimize recovery. This is primarily done through water and carbon dioxide (CO2 ) floods. At the Snipe Lake oil field in Alberta, Canada a 5.1 magnitude earthquake occurred in 1970; the earthquake was associated with the extraction of hydrocarbons using secondary recovery methods (fluid injection). Studies have indicated that these procedures may infrequently cause earthquakes ranging from magnitude 1.9 to 5.1 (Davies and others, 2013), with the majority of the earthquakes occurring at the low end of the observed magnitude range.

Fluid injection into the subsurface is a common procedure around the world and has been so for many decades by governments, municipalities, and various industries. This process is done to dispose of wastewater or chemicals below a serviceable water aquifer and to assist in the extraction of hydrocarbons located in oil and gas reservoirs. Other parameters that can contribute to induced seismicity related to fluid injection include the temperature and volume of the fluid injected, injection rates and pressure, proximity to faults, geologic formation targets, and the injection depth (Davies and others, 2013).

Over the last few years, there has been an increased interest in induced seismic events that may be related to injection/disposal wells. This has primarily been in Oklahoma, Texas, Arkansas, Colorado, New Mexico, and Ohio where recent earthquake activity potentially related to injection/disposal wells has occurred. These states are currently investigating the possible correlation between earthquakes and injection/disposal operations with industry, U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (EPA). Induced seismic events in these and other cases appear to have some or many of the following general characteristics and observations:

• Associated with some “higher volume” injection/disposal wells (injecting hundreds or thousands of barrels per day); injecting fluids into “deep” (thousands of feet below the surface) rock formations.

• Associated with wells that require pumping (pressure) to dispose of the fluids versus wells that take fluid by means of gravity only.

• An area immediately around the well (within a few miles) suddenly experiences many small earthquakes (swarms/clusters) that are below magnitude 2. A few earthquakes of up to magnitude 5 have also been reported.

• Appear to be associated with fluid injection into relatively competent rock formations (well consolidated) and/or in formations that are relatively near basement rock (within a few thousand feet).

• Geologic faults exist in relative proximity to the well bore (within approximately 0 to 5 miles). The faults do not typically extend to the surface and are not recently active (Holocene aged, approximately 12,000 years to the present).

• Appear not to be related to wells undergoing active drilling operations.

The complete report is available here.