MIDLAND, Tex. — In the land where oil jobs were once a guaranteed road to security for blue-collar workers, Eustasio Velazquez’s career has been upended by technology.

For 10 years, he laid cables for service companies doing seismic testing in the search for the next big gusher. Then, powerful computer hardware and software replaced cables with wireless data collection, and he lost his job. He found new work connecting pipes on rigs, but lost that job, too, when plunging oil prices in 2015 forced the driller he worked for to replace rig hands with cheaper, more reliable automated tools.

“I don’t see a future,” Mr. Velazquez, 44, said on a recent afternoon as he stooped over his shopping cart at a local grocery store. “Pretty soon every rig will have one worker and a robot.”

Oil and gas workers have traditionally had some of the highest-paying blue-collar jobs — just the type that President Trump has vowed to preserve and bring back. But the West Texas oil fields, where activity is gearing back up as prices rebound, illustrate how difficult it will be to meet that goal. As in other industries, automation is creating a new demand for high-tech workers — sometimes hundreds of miles away in a control center — but their numbers don’t offset the ranks of field hands no longer required to sling chains and lift iron.