Polymerization induced by radicals may convert normal alkanes into resins or waxy compounds between 300°C and 450°C and resins into asphaltenes at temperatures above 450°C. The nature of this chemical conversion was studied by the use of extracted model compounds and of natural crude oils during isothermal and constantheating rate pyrolysis. A thin bed reactor made from sinter glass which represents the properties of the porous medium was used.
Results of the study show that in the temperature region below 450°C the amount of resins in the crude oils determines the reaction rate of combustion, whereas above 500°C the amount of aspaltenes dominates the reaction rate constant. This tendency was observed with model substances as well as with dead oils, independently of the analytical method applied. Consequently, a large variety of different crude oils from paraffinic light oils to asphaltenic oils is able to produce the required fuel for in situ combustion, provided that the pyrolysis temperature is kept within certain limits. Temperature control in the process is achieved by a variation of the water-oxygen ratio of the injected fluids.