Just accepted an offer with Halliburton but I don't understand the pay.

I have zero O&G experience but 11 years experience as a welder pipefitter and 4 months experience with my class A cdl driving flatbed. Halliburton hired me as a OA2 for cementing. The pay is $18 per hour. But they also said on the job description average pay is 90k annually for that role. They're also giving me a stipend of 400 a month and 45 a day per diem.

I've seen other people talking about 3-4k a month on the cement side. Is it normal to have such a low hourly wage but make a high income of 90k a year?

Position is in Fort Lupton, Co.