Your friend who is working in Qatargas must be working in offshore, offshore salaries are always higher than onshore. Your basic salary plus you will be getting transportation allowance, location allowance, shift allowance etc...accommodation will be provided for  those who are working in locations like Dukham, Raslaffan etc.. You cannot negotiate your salary after singing the contract. But You will be getting an yearly increment. percentage varies from 3 to 10 %.  

You cannot move to another company as you cannot get release from QP.