Two years ago, East Texas’ Deep Bossier was one of the hottest unconventional plays in the U.S. EnCana Corp. had just purchased Leor Energy’s assets in Amoruso Field for $2.5 billion, and the best wells in the deep, high-pressured, high-temperature formation were ranked among the top 20 U.S. gas wells annually.

But in the past year, faltering gas prices have muffled the roar of production from the play’s Amoruso and Hilltop fields, in Leon and Robertson counties. The Deep Bossier is taking a back seat to EnCana’s land-retention strategy in ...