Investigation of water displacement process in pipelines: An improved mechanistic model and its numerical implementation

Multiphase flows are very common in industrial operations. In offshore oil and gas production, transient processes in long pipelines can lead to water accumulation, which must be removed using gas–oil mixtures. The slug flow pattern, characterized by the intermittent passage of elongated gas bubbles flowing over a liquid film, followed by liquid slugs that may contain dispersed tiny bubbles, is usually observed under these flow conditions and adds complexity to the phenomenon. Therefore, optimizing the complete removal of this water is crucial to avoid flow assurance issues. In this context, the present study proposes the development of a mechanistic model and its numerical implementation, aiming to estimate the time required for the removal of a water film displaced by a gas–oil mixture in a slug flow pattern within a 5° upward-inclined pipe. The present work also addresses the results of computational simulations performed using a commercial multiphase flow simulator, which predicts the trends of transient shutdown and restart processes in a pipeline, providing insights for the mechanistic model. Both the proposed model and the simulations provided consistent results, suggesting that higher gas phase fractions can accelerate water removal. However, the proposed model estimates that the mechanism of water displacement occurs through a liquid film, in contrast to the results generated by the simulator, which show displacement by a plug at the beginning, followed by a liquid film for the final removal of water. In addition, increasing the superficial velocities of gas and oil improves the ability to displace water in both approaches. As a next step, the results will be compared with the data from an experimental campaign and presented in a further work. This will enable the validation of both the simulations and the model against experimental data, as well as the identification of potential improvements.