Where does all the carbon dioxide in volcanic eruptions come from?
Titan has an atmosphere composed of about 1.5% methane, a hydrocarbon.
https://biofuels-news.com/news/one-step-methane-to-liquid-fuel-breakthrough/
>The researchers from the University of Liverpool have developed a plasma synthesis process for a direct, one-step activation of carbon dioxide and methane into higher value liquid fuels and chemicals such as acetic acid, methanol, ethanol and formaldehyde. Their findings have been published in the journal Angewandte Chemie.
>Converting carbon dioxide and methane into liquid fuels and chemicals using single step processes such as catalysis has proven a significant challenge because they are both inert molecules. Typically, the conversion will require high temperature, energy intensive syngas production process and high pressure syngas processing for chemical synthesis.
Hydrocarbons can and do form under conditions of high pressure and temperature.
The problem I have with the plankton theory is that we see oil formations outside oceanic crust and deeper than can be explained by the theory. Further, there is little contamination by calcium or nitrates that would form a large portion of the deposits.
"Sweet" and "sour" crude oils as well as heavy vs light varieties tends to have less to do with what life existed at the time and more to do with the geology closer to the mantle.
There is also the problem that wells filling back up is something of the standard rather than the exception.