The Austin Chalk, a vast underground ribbon of rock along the Gulf Coast, is garnering new attention this year, with drillers including ConocoPhillips and EOG Resources Inc. trumpeting efforts in an area the industry largely wrote off 20 years ago. Just last week, private-equity giant Blackstone Group LP sold royalty rights in the region for more than $400 million. The revival is the latest testament to the oil industry's improved health, with crude prices near $70 a barrel after a painful three-year slump.