A new study has established a direct link between injection of large volumes of wastewater from oil and gas activities into rocks deep beneath the surface and earthquakes.
Stanford geophysicist William Ellsworth co-authored a paper published in journal Science wherein scientists have attributed 4.8 magnitude earthquake that rattled residents and damaged buildings in East Texas in 2012 to manmade activities. The study is the first to provide direct evidence of induced earthquakes using remote sensing technique called Interferometric Synthetic Aperture Radar, or InSAR.
Through the technique researchers measured ground deformations near the wells in East Texas where the quake occurred. InSAR satellites use radar to detect tiny, centimeter-scale changes in the shape of Earth’s surface. Scientists focused on four high-volume wells used for disposing wastewater, located near the town of Timpson, Texas, where the 2012 quake was centered. The four wells began operations between 2005 and 2007 and at their peak injected about 200 million gallons of wastewater per year underground.
Brackish water naturally coexists with oil and gas within the Earth. After extracting this slurry using hydraulic fracturing or other techniques, drilling companies separate the “produced water” from the oil and gas and then reinject it into Earth at disposal wells. But the key thing is the location where the wastewater is injected. Injecting wastewater at a depth of over 1 mile, two of the wastewater disposal wells the scientists examined lie directly above where the earthquake occurred. The other two wells injected similar volumes of wastewater, but at shallower depths, just over a half mile below the surface.
The InSAR measurements revealed that wastewater injection at the shallow wells resulted in detectable ground uplift up to 5 miles (8 kilometers) away but only a modest rise in pore pressure, which is the pressure of fluids within the fractures and cavities of rocks, at the depth at which earthquakes happen 2 or more miles below the surface.
Increasing pore pressure within a geologic fault can cause the two sides of the fault to slip and release seismic energy as an earthquake.