Study On Phase Equilibrium Of Oil-gas-water-hydrate-wax Complex Multiphase System

Phase equilibrium simulation is the basis of hydraulic calculation and analysis of multiphase flow.For subsea multi-phase pipeline,high pressure and low temperature may cause the risk of simultaneous formation of wax and hydrate in the pipeline.Therefore,phase simulation is significant for the safety assurance of subsea pipeline flow.This paper studies the phase equilibrium of complex system containing wax and hydrates,and applies the results to the phase equilibrium software developed by the project group,which enriches and improves the computing function of the software.In the theoretical research,the algorithms based on the conservation of material and the minimization of Gibbs free energy are compared and analyzed,and the algorithm of gathering phase number judgement process and flash calculation process in one is innovated.The ChenGuo model and vdW-P model are used to calculate formation conditions of hydrate in pure water and salt/alcohol containing system.The ChenGuo algorithm and Gibbs free energy minimization algorithm are applied to calculate the complex phase equilibrium of oil-gas-water-hydrate system.Based on the above research,the phase behavior of wax and hydrate coexistence system is calculated and analyzed in combination with Yang model,and the phase equilibrium law of oil-gas-water-hydrate-wax complex multi-phase system is obtained.In the aspect of software development,first of all,the flash module is perfected on the basis of previous work,which enriches the selection of algorithms.Secondly,the hydrate module is developed independently,in which various functions are provided,such as the calculation of hydrate formation conditions/formation curve,the critical minimum dosage of hydrate inhibitor and PT flash of hydrate containing system.