Phase behavior prediction of petroleum fluids with minimum characterization data

Abstract

A new accurate and efficient computational method is presented for property calculation and phase equilibrium prediction of petroleum fluids using a minimum amount of input characterization data. This method is based on the combination of the discrete thermodynamic framework of the light components and a continuous thermodynamic characterization of the plus-fraction in petroleum fluids. The key features of the proposed method are the facts that: (i) the light fraction is specified by a definite number of discrete components with known characterization parameters; (ii) the plus-fraction is characterized by a generalized continuous distribution function in which three average plus-fraction properties, namely, the average molecular weight, the average normal boiling point and the average specific gravity, appear as the input data; (iii) there is no need for this method to characterize various families of hydrocarbons which may be present in the petroleum fluid plus-fraction; (iv) the model is applicable to any equation of state (EOS) and any set of mixing rules and combining rules; (v) the conventional multi-component phase behavior packages as well as continuous (or semi-continuous) phase equilibrium algorithms can be used with this model to predict the equilibrium ratio, gas/oil ratio, and other petroleum fluid properties; (vi) this model has the potential for application in phase behavior predictions with solid deposition which is the case with waxy and asphaltenic condensates and other crude oils. The proposed model is applied for vapor–liquid equilibrium calculation and bulk, liquid and vapor, phases property prediction of several reservoir fluid mixtures for which experimental data are available with success. This method is accurate because it predicts the properties of petroleum reservoir fluids as precisely as any other existing method. It is efficient because it removes the guess work for the characterization of the plus-fraction which has been the major barrier in the efficient calculation of bulk and phase equilibrium properties of petroleum reservoir fluids.