ABSTRACT: The central United States is experiencing an unprecedented surge in earthquakes that began in 2009, rising from an average of 21 magnitude 3 and larger quakes to over 650 in 2014 alone. This increased earthquake activity is found in just a few concentrated regions around the country, with the lion’s share in Oklahoma. In 2014 there were more magnitude 3 and larger earthquakes in Oklahoma than there were in California. The increased earthquake activity is limited to areas of new and emerging oil and gas production and is undoubtedly caused by some of the techniques they use.
With a focus on oil and gas production and related techniques, I will discuss the many ways that humans can cause earthquakes. In the case of fluid injection, the primary source of the recent increase in earthquake rate, the fluid pressure increase from injection can be transferred many miles from the injection point. This fluid-pressure increase, in effect, lubricates the faults, making them more prone to slipping in earthquakes.
Recent research shows that the rate at which injection occurs strongly influences whether earthquakes will be induced. Areas with higher injection rates are more likely to have induced earthquakes. Other parameters, like the total volume injected and the depth of injection, are also believed to affect the likelihood of induced earthquakes. Additionally, local geological conditions are important. Despite similar injection practices, there is very little injection-induced seismicity in North Dakota in stark contrast to Oklahoma.
Given that these earthquakes are human-caused, there is hope that they can be minimized or even stopped. Slowing or stopping injection, changing injection depths, or trucking fluids to other locations have all been suggested as ways to curb induced seismicity. Regulators in a number of states have taken notice of the increased seismicity and are taking action to reduce the likelihood of damaging temblors. With future research to improve our understanding of fluid-injection induced earthquakes, we may be able to reduce their likelihood, something that is not possible for natural earthquakes. To accomplish this, though, it will require cooperation between all the stakeholders, including academic scientists, regulators, and the oil and gas industry.
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