Coal and petroleum are NOT from ancient life.
Methane is a an extremely common compound and it was around when earth coalesced. As the methane trapped in the mantle escapes and rises through the crust it collects under pressure and the heat + pressure compresses it into heavier hydrocarbons.
This is abiotic theory in a nutshell.
There are coal specimens that show plant structures but I believe you are right about oil and natural gas. It seems to me that oil is a naturally occurring substance as unrelated to fossils as iron ire is.
Nope.
And DUH!