Scientists studying the phenomenon have long suspected that the culprit could be the recent boom in the oil industry, but other extraction method known as hydraulic fracturing, or fracking, was also thought to be the cause. Fracking creates micro-earthquakes with high-pressured water and chemicals to brake up underground rock and free trapped gas, which has created much controversy, since some link it to an increased seismic activity.
Stanford's Ph.D. student Rall Walsh and professor Mark Zhoback have found that the state's rising number of earthquakes coincided with dramatic increases in the disposal of salty wastewater into the Arbuckle belt, a 2,100-meter-deep sedimentary formation under Oklahoma.
Walsh and Zhoback's study is published this week in the peer- reviewed journal Science Advances and will likely shake, metaphorically, Oklahoma's oil industry. "When you produce 10 barrels of oil in some of these areas, you also get 10 barrels of water along with it. You can still make money if you skim off the oil and sell it," Walsh told Xinhua. However, this process leaves companies with a lot of water to get rid of.
The Safe Drinking Water Act regulates how people dispose of the water - they can not just pour it into a river or lake. To get rid of the salty water, the companies dump the waste fluid into disposal wells, some of them injecting large volumes deep underground. Most of these wells pour onto the same rock layer - the Arbuckle group.
"The bottom of the Arbuckle formation is rock layer, right on top of a crystalline basement that has faults in it," Walsh said, "some (not all) of those faults are active today, but the ones that are active, are also the ones that are permeable, so fluid can flow along them."
The large volumes of water act like a fluid skate, skidding the active faults in the Arbuckle formation and creating the seismic activity. Comparing their theory with empirical tests in their lab, the researchers found a direct correlation between the number of earthquakes and the disposal wells.
"In the areas where the injection rate increased significantly, earthquakes started happening," the researchers said. Wherever there were salt water wells, Walsh and Zoback recorded 71 percent increase in the seismic activity. In nearby areas where there wasn 't much saltwater disposal, there were comparatively fewer earthquakes.
Hydraulic fracturing, as had been stipulated in the past, was not the culprit behind Oklahoma's earthquakes, according to the study. In fact, Walsh believes that when done responsibly, fracking is a safe method to extract gas from the earth's guts. " Sometimes fracking is done next to an active fault that can make it slip faster, but if the required research is done, it's easily avoidable," he said.
Source:Xinhua - globaltimes.cn
20/6/15
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