Well, hydrocarbons have been detected in comets and asteroids as well as in the atmospheres of other planets and moons. I think it’s quite reasonable to assume hydrocarbons are abiotic.
Hydrocarbons are one of the building blocks for life imo. Particularly after seeing the algae and fish blooms which followed the Deepwater Horizon “tradgedy”.
When there is a lack of oxygen, methane is going to be lowest energy state for carbon and hydrogen. Depending on ratios of atoms, ethane and few larger molecules will exist as well.
Let me know when you find a substantiated claim for the Paraffins, Naphthenes, Aromatics and Asphaltics that make up the majority of crude oil composition.