Yes, you can claim per diem for your travel expenses, but only if this is considered to be a temporary
job, expected to last for less than one year. If this is your
permanent job site, and you work at the oil field for 21 days, then return to your
home, and have no main job location at your home, the rig location would be
considered your tax home, and you would not be able to claim travel expenses. See the discussions that follow:
https://ttlc.intuit.com/replies/5838564