An acid issue
The question keeps coming up about what kind of chemicals gas and oil companies use in fracking. I used to do fracking.
In 1958 I worked for an oil well servicing company in North Dakota. At that time we called it “acidizing” a well.
We used concentrated sulfuric acid. We sent a heavy iron “e-gun” down the well to the geological formation we wanted to “fracture.” The e-gun fired special “bullets” into the surrounding formation, providing channels for the acid to flow into, and open up, the oil-bearing formation.
I don’t recall that we pumped out the acid afterward. That was a picky detail we didn’t have to worry about.
From a Google search I found that the mix of chemicals is more sophisticated now and uses hydrochloric acid. But the main ingredient is still acid.
We don’t know how far the chemicals go or how big a cavern is eaten away under our feet.
The drilling companies pump out (how much?) of the acidizing fluid. But there has yet to be found a satisfactory method for disposing of the used fluid. Marine scientists report that the oceans are becoming more acidic.