About 99 percent of all the hydrocarbons in oil and natural gas are derived from the compressed, heated remains of ancient living organisms like zooplankton and algae. These critters were buried under layers of sediments five to 10 miles beneath the surface of the Earth.
Yep, these "critters" took their burials VERY seriously... LOL!
Fact is that there is NO CHANCE that the hydrocarbon stores of planet earth have a biogenic origin, despite the insistence of the traditional minded. First of all, the numbers just don't work out. Secondly, the traces of micro organisms found in many higher molecular weight hydrocarbon deposits did not necessarily precede the existence of the hydrocarbons. And there are quite a few locations were oil has been found in and beneath igneous formations. All in all, the biogenic theory of the formation of high molecular weight hydrocarbons is essentially a fairy tale, and like most fairy tales, they are meant for entertainment, not for edification.