There's been some debate about how much oil Iraq does or doesn't produce and who controls it.
The other important aspect is
how this oil is controlled, as well as by whom. Just a few years before the invasion and by some diabolical coincidence, I'm sure, Iraq started
selling its oil in euros, not dollars.
Now, if all the middle eastern countries started selling their oil in euros, that would potentially be very bad for the US both politically and economically.
(here's a quick analysis)..
One of the first things the US did after the invasion was to return Iraqi oil sales to dollars and to convert back into dollars all Iraqi foreign currency reserves,
So, as well as managing the world's third largest oil supply, the US also sent a message to other countries contemplating such 'follies'.
ofcourse, there are loads of other motives for the invasion besides oil, but I haven't got the time to go into it right now.
"In life, you have to face that some days you'll be the pigeon and some days you'll be the statue."