Factors Affecting Coking in Heavy Oil Cores, Oils and SARA Fractions Under Thermal Stress

Abstract

Abstract In previous work we demonstrated that minerals influence coking, combustion, and oil displacement. The effect is significant and seeminglyreservoir-specific. The magnitude and specific details, however, are much lessunderstood where the factors of surface area or the catalytic nature of themineral matrix are concerned. We recently performed a systematic study of thisphenomenon as part of Phase I of Saskatchewan Research Council's multiclient Thermal Studies project. A number of native cores from several heavy oilreservoirs, along with their corresponding matrices and oil thermal properties, were investigated. The results indicated that the surface area, as well as thesurface activity of the minerals, the asphaltene contents, and the nature ofthe oil, played a major role in coke (fuel) formation, depending on thereservoir type. Exploratory isothermal low-temperature oxidation (LTO) kineticstests on core materials, however, yielded somewhat conflicting results. It wasconcluded that in the rather complex oil system, several competing oxidationreactions interfere in some of the temperature domains, rendering the rate datasuspect. We felt the need to separate the oil into simpler and chemically morerepresentative constituents which would make the studies on oxidation andthermal cracking reactions more meaningful. We have adopted the existingseparation technique to obtain such fractions, i.e., saturates, aromatics, resins and asphaltenes (SARA). In previous work on some neat SARA fractions andin current work on several synthetic SARA cores, we have shown that thechemical group types tend to pyrolyse and produce coke independently of eachother. Therefore, the solid fuel formed from pyrolysis can be predicted from SARA test data for the whole oil or core sample. A meaningful experimentalapproach for the kinetics study of SARA fractions and synthetic cores will bediscussed in the text.