ervoir Oils by CPA EoS via a new Approach Based on the Asphaltene Molecular Structure

In this study, a new approach based on the molecular structure of asphaltene is developed to model asphaltene precipitation by the cubic plus association equation of state (CPA EoS). The accuracy of the proposed approach has been proved by reproducing the experimental data of asphaltene precipitation in two different live oil samples. In this approach, five similar association sites were assigned to the asphaltene molecules. Self-association between the asphaltene molecules and cross-association between the asphaltene and heavy hydrocarbon component were considered. The critical pressure of the heavy component was tuned using a single experimental bubble point pressure of the oils. Results revealed that the approach is able to predict the bubble point curve of the oil samples with the average absolute relative error (AARE) of lower than 1.54%. To model the asphaltene onset point, the cross-association energy between the asphaltene and the heavy component () was considered as the only tuning parameter of the model. It was assumed that the  was temperature-dependent and three different dependency were considered. The results showed that the cross-association energy is inversely proportional to absolute temperature. The CPA EoS reproduces the asphaltene onset point of the oil samples with the AARE of lower than 5.50%. At reservoir temperature, the asphaltene onset pressure for the two reservoir oil samples is 527 and 262 bar which is predicted by the CPA EoS as 502.5 and 250.4 bar respectively. As a conclusion, the proposed approach can not only predict the bubble point pressure but also accurately predict the general trend of asphaltene onset pressure with temperature.