Abstract
The thermodynamic description of wax deposition is a relatively new approach to solving the problem of wax precipitation, which the oil and gas industry has been struggling with for a long time. Many models exist in the literature to predict the thermodynamic conditions under which the first paraffin crystal is formed. The first task in all models is to determine the stability of the hydrocarbon mixture in order to define the possibility of wax precipitation. The stability of a mixture is determined by the thermodynamic behavior of the phases of a multicomponent mixture, namely, the presence of all existing phases in equilibrium. To this end, a new stability algorithm with Gibbs energy minimization to determine the wax precipitation in hydrocarbon mixtures has been developed. The algorithm is based on multi-solid thermodynamic model with EOS concepts. The main criterion for stability is the existing of the mixture at its global minimum. Proposed stability analysis predicts whether a given mixture will be split into multiple phases or will exist as the single phase at a given temperature and pressure conditions. The model was proven with 6 samples from fields X and Y showing the instability of original petroleum mixtures that agree with the real behavior of the oil in in-situ conditions. The results of the new stability algorithm are comparable with the results of the models presented previously. The main advantage of the method is its simplicity and reliability.