These companies are not legitimate. You can verify the existence of a company in Abu Dhabi by looking it up on the official portal of the government's registry and doing a search of their database: https://cbls.economy.gov.ae/Search_By_BN.aspx You will not find either company on the register, where they should be for tax purposes.
I have also looked at the domain registration information for the oil comany's website. What I have found is that the website is only 22 days old. It did not exist before May 10, 2021. It also is only registered for one year, the least amount of time you can register a domain for. This is the sign of a fly-by-night website and an almost certain scam.
Finally, you hit the nail on the head when you told me that this does involve a job offer but their visa process is different and requires payment from you. That's one of the hallmarks of a job recruitment scam.
The names of the companies supposedly offering the job change, though they are usually actual companies that most people have heard of. However, the job itself is not real. It is simply an excuse to phish for sensitive personal information about you and to steal your money.
Here's one warning about such scams:
https://legaladviceme.com/legal-blog/138/scam-alert-fake-uae-job-offers There are many others.
Other hallmarks of the scam:
-- the job is offered out of thin air or on the strength of your online resumé that you posted on some internet site;
-- the position is given to you with only a perfunctory interview via Skype or something along those lines;
-- The position is offered to you before it's even established that you are qualified to enter and work in the UAE; and
-- There is money you have to pay in order to qualify.
If this were real, the company would be sponsoring you and would have vetted you completely and paid all immigration and relocation expenses. Also, frankly, it's highly unusual that a major company would recruit from another foreign country to serve in their UAE branch unless whatever skills you have are so unusual that they couldn't be matched by someone already in Abu Dhabi.
Don't send any money. You don't have a job. You'll just be throwing your money away.
I'm sorry to be the bearer of bad news.