Like many other oil-field workers, Chris Sabulsky spent years working a schedule known as “14 on, 14 off:” two weeks at an oil or gas well somewhere followed by another 14 days at home in East Texas, fishing for bass and crappie. But now Mr. Sabulsky, 48 years old, is spending his days sending out résumés, calling acquaintances to see if they know of job openings, and pondering his future. His job managing hydraulic-fracturing, or fracking, operations at well sites evaporated in February after the oil-price plunge last year. Fracking, which uses water, chemicals and sand to free oil and gas from shale formations, has been a crucial factor in the U.S. […]