Prediction of the phase behavior of reservoir fluids requires modifying equations of state and improving characterization methods. In this work, besides the cubic equations of state (PR and SRK), a statistical EOS called PC-SAFT has also been employed to construct a collection of integrated characterization methods based on the structure of the corresponding equations of state. One of the major problems in reservoir fluid modeling is petroleum fractions, which are unknown hydrocarbon mixtures with unspecified components and compositions. In fact, characterization methods are needed to identify the nature of such unknown mixtures. Molecular type analysis methods are one of the most effective approaches applied to characterize petroleum fractions. The two best-known methods in this field are the PNA and SAP analyses in which a petroleum fraction is divided into three (Paraffinic, Naphthenic, and Aromatic) or (Saturate, Aromatic, and Ploy-nuclear aromatic) homologous groups. A generalized model is initially developed to predict the molar composition of the pseudo-components yielded from the main fraction. The model should be able to predict both the PNA and SAP compositions of the fraction based on its physical properties (Mw,SG,T_b). Afterward, some other generalized models are also developed to estimate physical properties and EOS parameters for the pseudo-components derived from the PNA or SAP analysis. Subsequently, a new method is proposed to calculate the volume translation coefficients for cubic equations of state and a lumping method is eventually put forward to combine pseudo-components after completing the property estimation. Having provided all required models, the characterization method is completed and can be used for the phase equilibrium calculations using the three equations of state mentioned. The second approach that will be addressed in this work is the characterization method based on the distillation curve. For this purpose, two different approaches are initially pursued to construct two diverse models, which possess the capability of distillation curve prediction for petroleum fluids based on their physical bulk properties. After providing predictive models for the distillation curve construction, the concept of characteristic cut points yielded from the atmospheric crude oil distillation unit is used to divide a petroleum fraction into some better-known pseudo-components. Furthermore, some new models are developed to predict physical properties and EOS parameters for pseudo-component derived from the distillation curve. The constructed characterization method is subsequently used in the phase equilibrium calculations to model reservoir fluids. The outcomes are then compared against the corresponding experimental PVT data. Finally, nine different characterization methods were obtained from these two points of view. The performances of the proposed characterization methods were totally compared to each other and compared to experimental PVT data of 20 diverse oil samples. The eva‎luation of results revealed that the most accurate characterization method was related to the condition in which the PC-SAFT equation of state has been coupled with the PNA analysis. The mean of AAD values was 5.4 % for this case. Moreover, a comprehensive comparison was also conducted between the proposed methods and previously existing characterization methods. The results showed that the proposed methods could considerably reduce deviations to one-third of the average of errors that occur in the previous methods with an AAD of 18.3 %.

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روح الله هاشمي

مسعود رياضي، عظيم كلانتري اصل، عليرضا خزعلي، محسن محمدي