Into the night sky, a modest flare from the Bentley 34-1H bore the news in early December of Louisiana’s horizontal Eagle Ford oil and gas-liquids discovery well along T.L. James Timber Road, just west of Alexandria. “My head is still spinning,” admits Bill Pritchard, chairman of Houston-based Indigo Minerals LLC, which owns most of the acreage across the state’s newest shale fairway that may be as much as 100 miles wide.

While the well met with mechanical-pump interruption in its first several days online, it made 543 barrels of oil ...