By “largely abiotic means”, I do not preclude the vast stores of natural gas and petroleum found in sedimentary deposits. As may or not may not be known, the floor of the ocean, in fact any body of water deeper than about 500 meters or so, the constant temperature is about 4 degrees Centigrade and at least some multiple of the atmospheric pressure at sea level. Under these conditions, any methane gas (which exists both as one of the elementary building blocks of the universe and as an end product of organic decay) combines with water to form a substance called “Methane Hydrate”, a substance that stays stable so long as the temperature remains below about 6 degrees Centigrade or so. As it is just slightly heavier than fresh or saline water, it remains on the bottom, gradually being silted in the ooze at the bottom. As this ooze solidifies into sedimentary rock, it is trapped and becomes a natural gas reservior, to be tapped millions of year later.
In the presence of certain catalysts, the methane molecule will reform into longer and longer chain hydrocarbons, thus the accumulation of petroleum in these deposits.
Oil does not “break down” during the distillation refinement process, it is separated into fractions with different volatilization and condensation points. The very long chain hydrocarbons may be successfully “cracked” by passing the substance in vapor form over a catalyst that breaks down the long carbon chain, and adds hydrogen at the point where the break in the chain occurred, creating two or more molecules of a much “lighter” petroleum fraction.
In the process used in converting organic matter into light hydrocarbons, called “thermal depolymerization”, the other vital ingredient is - water. At about 400 degrees and pressure ranging from 4 to 10 times atmospheric standard, the organic matter, be it turkey intestines, used condoms, old mattresses, lumberyard waste, or even old asphalt, is converted at a very rapid rate (less than two hours) into various kinds of light petroleum and some mineral ash, with a separate quantity of some of the water that was originally incorporated into the process.
We shall NEVER run out of petroleum.
There is no oil/gas production anywhere outside of sedimentary basins.
Thermal depolymerization and similar process is essentially the source of all our oil/gas. As algae, planton and other biotics accumulate in the sediment, over time with increased heat and pressure they are broken down into the hydrocarbons we produce today.
The process hasn't ended, but it is a slow, slow process. If there process occurred anywhere near the world's present consumption over the hundreds of millions of year, the oil would be miles thick all over the world.