Compositional Modeling of Two-Phase (Gas/Water) Flow in Gathering and Transmission Pipeline Systems

摘要

The current work presents a fully-compositional tool for modeling systems exhibiting two-phase (gas-water) flow. The tool couples complex hydrodynamic and thermodynamic models to describe the behavior of fluids flowing in a pipe. Results show that the model is capable of predicting water condensation in the pipe, estimating pressure/temperature profiles, and handling different flow patterns and their transitions. Moreover, the model has the capacity of estimating the concentration of hydrocarbons, carbon dioxide, hydrogen sulfide, methanol, and other substances dissolved in the aqueous phase. Hydrate formation is related to the presence of methane, ethane, propane, butanes and nitrogen in a gas stream, while acid is expected to form when significant amounts of CO2 or H2S are present in the aqueous phase. The model developed in this study provides production engineers with an excellent tool for evaluating the potential formation of hydrates and/or acids in piping systems. Several cases were used to validate the model. Model predictions were compared against experimental data obtained by Eaton et al. (1967). The flow patterns and pressure profiles calculated by the model accurately matches experimental data. The pressure profile calculated is within 2.0% of the reported experimental values. Similarly, the average liquid holdup estimated was in good agreement with the values reported by Eaton et al. (1967). The model is capable of predicting the initial water condensation point in the pipeline and the concentration of different substances in the aqueous mixture. The tool givesproduction engineers important information on how much hydrate/corrosion inhibitors to inject and where, thus saving in the design, operation and maintenance of pipeline systems.