A new study from researchers at Stanford University has linked a 4.8 magnitude earthquake recorded in East Texas in 2012 to the now common oil industry practice of hydraulic fracturing (“fracking”) and the accompanying wastewater injection wells, through the use of satellite data, according to a new press release from the highly regarded university.
While it’s long been suspected that the 2012 earthquake — the largest recorded in the region to date — was caused/triggered by the injection of “large volumes of wastewater from oil and gas activities into rocks deep beneath the surface,” this research is reportedly the first to definitively link it to that practice.
“Our research is the first to provide an answer to the questions of why some wastewater injection causes earthquakes, where it starts and why it stops,” stated study co-author William Ellsworth, a geophysics professor at Stanford’s School of Earth, Energy & Environmental Sciences.
The new study utilized a remote sensing technique called Interferometric Synthetic Aperture Radar, or InSAR, to “measure 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.”
“Our study reports on the first observations of surface uplift associated with wastewater injection,” Ellsworth continued. “The detection of uplift when combined with well-injection records provides a new way to study wastewater injection.”
The press release provides more: “The team 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. Approximately 180,000 of these disposal wells are currently in operation in the United States, primarily in Texas, California, Oklahoma, and Kansas.” Wow, 180,000!
“You can think of the wastewater as ancient ocean water,” Ellsworth commented. “It’s too salty and too contaminated with other chemicals to treat economically, so the only viable solution at present is to put it back underground.”
The press release continues: “But where that wastewater is injected can make a huge difference. 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.”
At the shallow well sites studied, this did not happen, owing to a “nearly impermeable” rock layer underneath the associated injection sites — which prevented pore pressure from moving downwards towards the “crystalline basement.” (The crystalline base is a deep and faulted rock layer where some earthquakes originate.)
In contrast, at the deep-well injection sites, “the combination of stiffer rock and the impermeable ‘blocking formation’ above allowed the rising pore pressure to migrate downward and build up until it triggered earthquakes in 2012 along an ancient fault line. The quakes ended in late 2013, when pressures began to decline after wastewater injections were scaled back considerably.”
Ellsworth continued: “The recent upturn in seismicity in Oklahoma and Kansas commonly happens where injection occurs close to the crystalline basement, so we’re getting lots of earthquakes in those places. Injecting at shallower depth above a blocking formation would reduce the ability of the pore pressures to migrate to the basement and activate the faults.”
The new findings are detailed in a paper published in the journal Science.