Induced seismicity is a term used to describe earthquakes that are stimulated by human activities. The media commonly report on induced earthquakes incorrectly, fueling the misconceptions listed below. Because of this, policy makers and the public often have an incorrect or incomplete understanding of how and why they occur.
If HVHF technologies were brought to Idaho, the number of felt earthquakes would increase in an area not prepared for dealing with the effects of seismic activity.
Induced seismicity is largely caused by the injection of wastewater into deep wells underground where it can lubricate cracks in the rock called faults, causing earthquakes.
Below are several misconceptions about induced seismicity and corrections of these misconceptions.
Misconception: Fracking itself is causing all of the induced earthquakes. Correction: Fracking only directly causes a very small percentage of the felt-induced earthquakes observed in the United States. Most induced seismicity in the United States is a result of the disposal of wastewater related to oil and gas production.
Misconception: The wastewater injected in disposal wells is fluid that was used to frack the well (spent hydraulic fracturing fluid). Correction: The amount of spent hydraulic fracturing fluid injected into wastewater disposal wells varies among wells and states. In some states such as Arkansas and Oklahoma, the fluid injected into wastewater disposal wells is produced water. Produced water is the salty brine from ancient oceans that was trapped in the rocks. This water is trapped in the same pore space as oil and gas, and as oil and gas is extracted, the produced water is extracted with it. Produced water often must be disposed in injection wells because it is frequently laden with dissolved salts, minerals, and occasionally other materials that make it unsuitable for other uses.
Misconception: There would be no need for wastewater disposal if hydraulic fracturing were not used. Correction: Salt water is produced at virtually all oil wells, whether the wells were hydraulically fractured or not. This means that wastewater disposal remains a critical issue for both fracking and conventional oil extraction.
Misconception: Induced earthquakes only occur close to the injection well and at a similar depth as the well. Correction: Earthquakes can be induced at distances of about 6 miles or more away from the injection point and at much greater depths than the well.
Misconception: All injection wells (hydraulic fracturing and wastewater disposal) induce earthquakes. Correction: Most injection wells do not cause felt earthquakes. There are approximately 35,000 active wastewater disposal wells, and tens of thousands of wells are hydraulically fractured every year in the United States. Only a few dozen of these wells are known to have induced felt earthquakes. However, in some sense, all hydraulic fracturing induces earthquakes, although these are typically micro earthquakes. When production engineers hydraulically fracture, they are intentionally cracking the rock, causing small earthquakes that are typically less than magnitude zero.
2014 Seismic Hazard Map (USGS)
This map shows the seismic hazard in 2014 in Idaho. It can be seen that the southeastern region of Idaho, where there is the potential for unconventional drilling to occur has a higher peak ground acceleration (PGA) than other areas of the state. Peak ground acceleration measures how hard the earth shakes at a given geographic point and is commonly used in seismic hazard maps.
Below is a map showing the location of faults in Idaho.
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