gdave nails it. The biogenic theory provides us with a predictive science. It makes useful and validatable predictions. To expand a little. If you are looking for oil or gas you will start by looking for provinces with histories that suggest there were good biological sources present in the past, and which would have been around at a time where later geological processes would have buried them. Modelling things like sedimentary processes can sometimes help understand what is buried and where.
That is a very broad start. Various surveys of the area would be looking for features that could trap any resulting fluids. Understanding the broad geological features and history. But a critical part of this is to model the thermal history of the province. You need to cook the biomass just right. In particular if it is overcooked you get coal. (Coal is everywhere, but mostly useless, as it won’t flow up a pipe.) These basic guides can tell you if it is worth spending the big money on seismic and exploratory drilling.
So - somewhere where there was biomass on the surface, subsequently buried, proper thermal history. Find these, and you have good reason to commit the many millions needed in the next phase of exploration. And it works.