If I were to hazard a guess I would say the amount of abiogenic oil is negligible, relatively speaking. However, I also believe that the amount of oil that is the result of dead plant and animal matter is also negligible.
I reckon abiogenic or fossil oil distinctions are both true in a sense and both false in a sense - true in the sense that chemistry must allow for both to have formed, and both false because the conditions on which they are created are extremely rare. The earth's crust is primarily made up of oxygen and silicon, around 74%. The puzzle of planet Earth is its oxygen atmosphere. I would suggest that SiO2 has been broken up by micro-organisms deep in the earth, and under conditions oxygen poor conditions these micro-organisms do what they must to survive. Silicon is converted into Carbon and Hydrogen and/or Helium, depending on the circumstances, and Oxygen is used for respiration, and is also liberated, thus forming the oxygen of the atmosphere. This, of course, implies that micro-organisms under these circumstances can change one element into another.
SiO2 ---> Si + O2
Si ---> 2C + H2 or Si---> 2C + He
The oxygen from cracking SiO2 provides for respiration. Thus water and oxygen are produced deep in the earth by micro-organisms.
The silicon is converted into carbon and hydrogen for the building blocks of micro-organisms require for sustenance and reproduction. Helium may be another product of this reaction.
The result is that in a sense oil is both abiogenic and biogenic. Abiogenic in the sense that the raw material is not biological, but biogenic in the sense that only through micro-organisms does the oil come into existence.
The Nitrogen in Earth’s atmosphere one might regard as anomalous also. This too can be accounted for by micro-organism action.
Si —> N2
Micro-organisms are not complex conscious beings. They cannot control what they do but they as a primitive life form will need, as all life forms need. They merely evolved to be able under certain circumstances to survive in deep earth conditions. But they would need to produce protein also. Nitrogen would be a natural byproduct of the reactions that keep them alive and reproducing. The abundance of Nitrogen relative to Oxygen in the atmosphere is also indicative of the micro-organism action deep in the earth.
Kervran is the most modern example of the notion of transmutation, and it is his idea that has generally been rejected regarding the power of micro-organisms. I would suggest further that in other planets this sort of action may be going on. Transient Lunar Phenomena may be, for example, a result of transplanted micro-organisms from Earth ending up on the moon, eating away at Lunar silicates and producing occasional outgassings.
If there is anything to Earth Crustal Displacement, what better a lubricant for it than oil deep in the bordering layers that would allow for a shift to occur under the circumstances implied by Charles Hapgood.