Engineering design of gas-condensate pipelines with a compositional hydrodynamic model

Gas condensation in pipelines designed to transport natural gas is common. The radical difference in the engineering design required for this system, compared with that required of 'dry gas' pipelines, makes the problem of significant interest to the gas industry. Because the point and quantity of condensation is not usually known a priori, any attempt to develop a predictive capability for such a system must have an inherent means of providing this information. This requires a good coupling of the gas-phase behavior model with the appropriate hydrodynamic model. This work attempts to develop such a model. With a two-parameter equation of state (EOS) to describe the phase behavior of the natural-gas system, a multiphase hydrodynamic model developed from fundamental fluid dynamics is used to described the hydrodynamic behavior of the resulting two phases. The model, which consists of a system of nonlinear algebraic and ordinary differential equations (ODE's), was solved numerically. Output from the model solution includes quantity of condensate at any point in the pipeline, pressure drop, and other hydrodynamic variables. The model can predict the various engineering parameters of interest in the design of such pipelines and could be used for feasibility studies and for optimal location of fluid-handling equipment.