Improvement of Whitson algorithm for chemical/gravity equilibrium calculations to compute compositional gradient in petroleum reservoirs

This work concerns to improve accuracy and convergence speed of Whitson algorithm, applied for calculating compositional changes in petroleum reservoirs. These improvements are implemented by choosing the proper calculated value of the parameter λ and using the more proper way to choose the pressure estimation in algorithm. In this method both liquid and gas phase calculations use just one reference point in calculations. Reference point is a point where certain compositions and pressure are set for a certain depth. Results of this improved numerical algorithm are matched well with the results of commercial software that validate this method. Results show that calculations would be more accurate by inserting some modifications into algorithm.