We have been given the a basic understanding of where the garden was.
Genesis 2:10-14, A river watering the garden flowed from Eden; from there it was separated into four headwaters. The name of the first is the Pishon; it winds through the entire land of Havilah, where there is gold
The name of the second river is the Gihon; it winds through the entire land of Cush. The name of the third river is the Tigris; it runs along the east side of Asshur. And the fourth river is the Euphrates.
And, also take int account that we were also told that man would never set foot in the garden again, and that an angel of the lord was dispatched to guard it with a fiery sword.
If you look at a map one can place two of those rivers on the map still, both are in what we now know as desert... Kinda what a place would look like if someone put it to a fire.. Or maybe what is meant by, guarded by a fiery sword. This would full fill that prophesy in that no man will ever set foot in the garden again. (Because we can't for all of the sand.)
In short the garden or what is left of it is buried beneath the desert (along with the other two identifying rivers.)
Maybe that is why there is so much oil there. Without a doubt it was lush at some point.