This like all the other commercial oil production sites, are located in sedimentary basins. Sedimentary basins are the accumulation of sediment, laid down from the surface.
You need to think in geological terms. Most folks cannot seem to wrap their minds around that spread of time. 1" of compacted sediment that took 1,000 years to accumulate becomes more than 6 miles deep in 400 million years.
And it isn't dinosaurs, that was a cartoon ad. The dinosaur is from Old Sinclair and other Oil ads because it was from rock laid down in pre-historic (dinosaur) age.
If you will learn a bit more about geology, including cap rocks, petroleum traps, etc, it can be come more clear.
So you are saying that petroleum is, as most believe, a fossil fuel?