U.S. oil firms use shale know-how to revitalize old oilfields

By Ernest Scheyder BURTON, Texas, June 14 (Reuters) - Among vineyards and cow pastures in east Texas last month, roughnecks started to drill in an oilfield that is 25 years past its production peak. Houston-based oil producer Wildhorse Resource Development Corp tasked the crew with breathing new life into the field by using technology developed for fracking shale rock. In the limestone and clay Austin Chalk formation, which stretches across south Texas into central Louis