I’m a geologist and worked in oil and gas exploration for 5 years. Oil (petroleum) comes from kerogen, which typically forms from plant matter buried at high pressure and temperature and then fills reservoirs underground or sometimes leaks to the surface. Scientists are able to fingerprint these oils and match them directly to source shale rock that is drilled in nearby wells. Oil would not have formed prior to the existence of certain types of life.

The hydrocarbons found on titan appear to be simpler hydrocarbons (including methane - natural gas) which are generated from organic compounds (uncertain whether caused by life or not).

This is all a question of abundance. Methane is easy for us to capture right now because there is a shit ton of it captured in geologic reservoirs. No one knows exact rates of regeneration, but given that it’s on a geologic time scale it is likely slower than the rate we deplete our reserves.

So we either find new synthetic mechanisms to create petroleum and nat gas or we eventually run out/pay more and more to extract per unit. Of course humans are creative and we have lowered the costs of extraction over and over since the discovery of oil.