CO2-miscible flooding for three Saskatchewan crude oils:: Interrelationships between asphaltene precipitation inhibitor effectiveness, asphaltenes characteristics, and precipitation behavior

Studies were conducted to determine the asphaltene precipitation inhibition effectiveness of three carefully chosen chemicals (dodecylbenzenesulfonic acid (DDBSA), nonyl phenol (NP), and toluene) during CO2 flooding of three Saskatchewan crude oils, as well as to evaluate the interrelationships between the chemicals' inhibition effectiveness, crude oil/asphaltenes characteristics, and asphaltene precipitation behavior (in terms of kinetic and equilibrium parameters). Results showed that both the asphaltene precipitation rate dependence on asphaltene content and apparent rate constant for asphaltene precipitation were strong functions of the paraffin fraction of the asphaltenes and the propensity of the asphaltene molecules for aggregation. On the other hand, the precipitation rate dependence on the amount of CO2 added was a strong function of the heteroatoms (nitrogen, sulfur, and oxygen) content of the oil and asphaltenes, the aromatic carbon fraction, and the degree of branching of the asphaltene molecules. The equilibrium parameter (onset point) increased with the paraffin fraction of the asphaltene molecule but decreased with the propensity of the asphaltene molecule for aggregation. In terms of kinetic parameters, NP with the -OH functional group in its molecule was most effective with the more-aromatic (and more-substituted and more-polycondensed) shorter-alkyl-chain-length oil, whereas toluene (the most-aromatic additive) was most effective with the least-aromatic oil. In terms of the onset point, all three chemical additives showed maximum effectiveness with the least-stable oil that had the lowest metal content, and in the asphaltenes molecules that had the lowest paraffin fraction, highest degree of condensation, highest aromatic carbon fraction, and highest propensity for aggregation.