CGG, a geological and reservoir services company, has completed a three-year, 1,566-square-mile seismic survey program for multiple clients in the Marcellus Shale fairway. The Paris-based company said the program is believed to be the largest combined onshore seismic survey ever conducted in the United States. It was completed in six phases that covered Lycoming, Tioga, Clinton, Centre and Clearfield counties in central Pennsylvania. The survey was aimed at providing a multi-client data library of shale acreage in the play to optimize drilling and completion programs. By the end of 2014, the company expects to make data from all six phases available, which draw from more than 118,000 shots and millions of receiver locations.