Kinetics of CO2-induced asphaltene precipitation from various Saskatchewan crude oils during CO2 miscible flooding

A molar CO2 programmed titration technique was used to evaluate the kinetics of CO2-induced asphaltene precipitation from three Saskatchewan crude oils (namely Steelman, 12-25-6-14w2 and D8-12-6-14w2) under isothermal (in the range of 300–338 K) and isobaric (at 17.2 MPa) reservoir conditions in a solids detection system (SDS) consisting essentially of a mercury-free, variable volume, fully visual, JEFRI PVT cell. The results show that the rate of asphaltene precipitation depends on, both, the asphaltene and CO2 contents of the oil. This work represents the first attempt at obtaining kinetic data for asphaltene precipitation from crude oil without any pretreatment of the oil as well as formulating a kinetic model that fits the data. Different values for the reaction order (m) of asphaltene, and the reaction order (n) for CO2 were obtained for the same oil at different temperatures. This shows that the mechanism for CO2-induced asphaltene precipitation was temperature dependent. Also, the values of n for all the oils at all the temperatures were much larger than the corresponding values for m. This shows that asphaltene precipitation is extremely more sensitive to CO2 content than asphaltene content, even though the contribution from asphaltene content in the oil cannot be ignored. The large overall reaction order (m+n>4) also provides the experimental evidence to confirm that asphaltene precipitation is not an elementary process.