Oil wells: proven relationship between waste water and earthquakes


In Texas, in 2012, an earthquake of magnitude 4.8 occurred, certainly triggered by the large volumes of water used in the drilling of oil wells injected in depth. Thus stated William Ellsworth (Standford University) in a work published in Science (abstract in English).

It has long been suspected that the wastewater injection process was linked to earthquakes, but the definitive test was missing so far.

Radio waves to measure the soil. The study used the SAR (Synthetic Aperture Radar) satellite scan, which measures soil deformations: in particular, it was used to analyze the situation near the wells of eastern Texas where numerous earthquakes have been occurring for some time, albeit of low intensity.

The InSAR satellites measure the time of return of the radio waves, from satellite to the surface, to calculate the distance with errors of a few millimeters: repeated passages on the same place therefore allow to verify the variations of altitude even of single points.

Image The location of the 4.8 magnitude earthquake of 2012 in Timpson (Texas), caused by the injection of wastewater into the underground. |

The work group led by Ellsworth focused on four wells where large quantities of waste water were released, in the area of ​​Timpson (Texas), where the earthquake of 2012 occurred. From 2005 to 2007, 200 million were injected of liters of water a year.

"The water used in the drilling is too contaminated with chemicals to be treated and then returned to" clean ", so it is preferred to inject it into the earth's crust, " explains Ellsworth. The four wells taken as models of study would have served to understand what can happen near the more than 180, 000 losing wells that are found scattered in the United States between Texas, California, Oklahoma and Kansas.

United States: human-induced earthquake risk maps

Better the shallow wells. Research has allowed us to understand that not all water injections produce the same effects.

When water is injected up to a maximum depth of 600 meters, earthquakes are rarer and less intense, because the fluid does not reach the rocks of the deep crust, where there are fractures (faults) that can be lubricated or put into motion by pressure.

Where the water is instead injected at considerable depths, over a kilometer and a half, earthquakes of strong intensity can also occur: in this case the fluid damages the fractures of the rocks, which move lubricated by the water itself, such as 'happened to Timpson.

With the satellites it has been possible to identify the oil areas where the waters go deeper, because there are fewer superficial deformations of the soil: an important fact to understand where an earthquake can potentially trigger.