Oxygen can be absorbed as CO2 in rocks like olivine ((Mg,Fe)2SiO4). That's one of the most common reactions in the world.
Several problems with this. Firstly there are a number of magnesite deposits where it has been demonstrated that the source of carbon is biogenic.
M. Orion Jedrysek 1, 2 Stanislaw Halas 1, 1997, The origin of magnesite deposits from the Polish Foresudetic Block ophiolites: preliminary δ13C and δ18O investigations, Terra Nova, Vol 2, issue 2, pages 154 – 159
As well this reaciton would form magnesite, silica and water. In this case you should expect close correspondence between ultramafic intrusive rocks, magnesite deposits and hydrocarbon accumulations. On the contrary there is virtually no correlation of ultramafics, magnesite with hydrocarbon deposits.
Again the main problem is you can't form complex hydrocarbons from methane as it requires chemical bonds to be created that require enormous amounts of energy. If you believe their claim that they form some ethane and butane you are still left with two problems...the enormous volumes of hexane, heptane etc in the crust globally and the fact you would have to hold these species in disequilibrium throughout their rise from the deep crust through to the shallow crust.
Notwithstanding all of that I am not aware of a liquid hydrocarbon that hasn't been matched based on carbon fingerprints to a source rock in hydrodynamic continuity with it.