The construction of unified compositional model is important for modeling of production surface network. The produced streams are described by different multicomponent PVT models, while total production calculation requires a single consistent PVT system. The method for constructing a compositional model which is optimal in terms of components number is proposed.
As a first step, all components from all initial mixtures are split by molecular weight into two groups: light and heavy, which are considered separately from that point on. The basis component set for the light group is constructed from the pure hydrocarbons and inorganic substances. Then the components from the light group are expanded over it using the method of numerical minimization. The objective function used is the sum of the moduli of the relative differences of corresponding parameters of initial components and their decompositions. The parameters considered are critical properties (pressure, temperature, volume) and the acentric factor. The condition of equality of molecular weights is enforced, to ensure the conservation of material balance during decomposition of the initial components. Two methods are proposed for the characterization of heavy components: either proceed the same way as it is done for the light group, with the construction of a corresponding basis, or use fractionation by the number of carbon atoms. All properties of the components of the final set are fully known after the above algorithm has been applied. Each component in the initial mixtures is decomposed using the resulting set of components with uniquely defined coefficients.
The proposed method is successfully used to construct a unified compositional model for production surface networks. The sources (pipelines or wells) with different PVT models are connected in the single production network computed by resulting compositional PVT properties.