"With just the addition of one rig and investment of about $400 million a year, we're going to be able to raise production by 50 percent and be cumulative cash flow positive by the end of 2020," Paul Ferneyhough, executive director of North America for Repsol said at the S&P Global Platts Global Energy Outlook Forum.

Repsol holds an interest in 168,400 net acres in the Marcellus Shale, one of the largest natural gas fields in the world, extending throughout the Appalachian Basin and stretching across Pennsylvania, according to its website.