A Continuous Mixture Computational Algorithm for Reservoir Fluids Phase Behavior

paeudocomponent method to 8 system containing various families of compounds, such as paraff ina, D velopment of compositional reservoir simulators is naphthenes, and aromatics, it ia neceaaary to extand presently hampered due to the complexity of the the pseudocomponent description of the mixtures up existing computational ●lgorithms of reservoir fluid to C20+ or more so that the experimental data can phaae behavior calculations. Through the be matched by the prediction. Phase equilibrium application of the theory of polydisperse fluid calculation for the latter case is intricate, and in mixtures wa have developed a new algorithm for addition to the difficulty mentioned above, a great reservoir fluid phase behavior calculation. In deal of computational tima will be necessary. Aa 4 for a typical system this algorithm a reservoir fluid is considered to nbted by Hathias ●nd Benson, consist of a continuous mixture with a defined . encountered in engineering calculations the molecular weightfcomposition distribution. The computational time depends primarily on tha terms proposed algorithm requires less computational time involving pairs of components in the equation of than the time required by the ●xisting state mixing rula summations. pseudocomponent VLE calculation methods. It is alao h alternative method which can significantly ahown that the new algorithm is applicable to reduce the difficulties mentioned above sterna from varietiea of equations of state and mixing rules. the idea of polydisperse (or continuous) Results of the proposed technique are compared with thermodynamics. That is, instead of mole fractions, results of the other ●xisting techniques, and with a density distribution function which is a function the simulated rnulti-pseudocomponent reservoir fluid of some measurable property such aa normal boiling mixture dsta. point, liquid density, or molecular waight is introduced to describe composition of many-component INTRODUCTION mixtures such as petroleum reservoir fluida. In complax mixtures, such aa petrolaum reservoir Initially, the concept of continuous mixtures was fluids consisting of a large number of components, ●ppliad in polymer solution theories and predi t-on it ia very difficult to identify components and their concentrations. Thus description of such of liquid-liquid ~eparation in such ●olutions~-i Aris and Gavalas introduced functional analysis m:.xturas by mole fractions of components is in the thermodynamic description of polydisperse practically impossible, and a simplified technique system and kinetics of continuous reactions such as which ia called “paeudocomponent method” haa been polymerization or cracking. Concerning petroleum generally used. By this method the lighter distillation, flash calculation schemes which are componanta (Cl to C6) are identified ●nd the heavier components (C7+) are splitted into ● based on simple models, such aa Raoult’s law, hfe been reported for ontinuoua mixtutos. 9-11 For number of fractions which are characterized by their example, Hoffmanl 6 preaentsd s numerical average boiling pointa, liquid denaitiva, and integration method. In this method, he ●dopted molecular weights. Then phase equilibrium integrated form of Clauaiu8-Clapeyron equation ●nd calculations ●re performad by ordinary thermodynamic Raoult’s law to compute vapor pressures of petroleum techniques in which ●ach fraction ia considered as a component. 1-3 fluids. He used Gaussian distribution with normal pure When applying the boiling temperatures considered as the independent variable to describe the vapor and liquid phasea. References and illustrations at end of paper, Similar procedures s Hoffman’s were presented by R~tzsch ●nd Kehlen,13 whoso treatment waa based on