Yet there is no doubt that biological organisms can manufacture oil as a byproduct.
Not only is there oil at different depths (because it is from different sources), but the oil is different.
Because one is created by biological process, the other is created by subsurface temps/pressures, and matter in a state we cannot even define as of yet.
THE KEY to understanding the abiotic process and it's validity, is to understand WHY the Earth generates oil.
Uh... to keep it from squeaking?