Maybe you have forgotten that one of the reasons Bush got congress, and the people, to agree to the invasion of Iraq was to assure us that the cost would be reimbursed from Iraqi oil?
Yes, Bush made promises to the American people that the operation wouldn't cost a lot and some would be reimbursed by Iraq, but that was pie in the sky wishful thinking. He did not strike any such formal deal with Shiites, Kurds or anyone else that stood to gain from our invasion (at least that I am aware of).
Again, I am not saying that they don't owe us, the problem is our reasons for going there had nothing to do with the seizing or taking over Iraqi oil. Iraq was Bush's attempt to deal with bothersome low hanging fruit and to establish a democracy in the heart of the arab world in an attempt to get Muslims to deal with their own problems rather than blame Israel and America for everything. To later decide to seize their oil would confirm every conspiracy theory arabs and anti American propagandist have about us - and achieve next to nothing in reducing the cost of gas.