A fracking boom isn't enough for U.S. oil and gas producers — they're now starting the re-fracking boom.
Wells sunk as little as three years ago are being fracked again, the latest innovation in the technology-driven shale oil revolution. Hydraulic fracturing, which has upended global energy markets by lifting U.S. crude oil output to a 25-year high, has been troubled by declines in oil and gas output.
The development highlights how producers must constantly invest and tinker, both to raise overall oil recovery rates that can be as low as 5 percent and to limit steep drops in production suffered by wells drilled into tight oil deposits.