From the Houston Chronicle:

The son of a poor Greek immigrant, Mitchell had an uncanny knack for finding oil.
During his career, he participated in drilling some 8,000 wells, including more than 1,000 wildcats.

He was a pioneer in the technology of hydraulic fracturing and horizontal drilling, using it to tap oil and gas in the Barnett Shale of North Texas in the 1980s and 1990s. The process launched a revolution in U.S. energy, and prompted international environmental debate. Oil giant, developer George Mitchell dies at 94 - Houston Chronicle