HOUSTON, July 27: George Phydias Mitchell, a petroleum engineer who transformed the natural gas industry by using hydraulic fracturing to pull the fuel out of shale formations, died of natural causes at the age of 94 yesterday. A native of Galveston, Texas, who rose from modest means to become a billionaire philanthropist, he was the chairman and chief executive officer of Mitchell Energy & Development Corp, which was sold to Devon Energy Corp for 3.5 billion dollar in 2002. (agencies)