Performance Evaluation of a New Transient Two-Phase Flow Model

Abstract

Transient gas-liquid flow is a common phenomenon in the drilling, workover and gas/oil production processes. Any change in the operating conditions at the inlet or outlet will introduce a transient response. Operations such as liquid unloading, under balanced drilling with gasified fluid, well control, cementing, hole cleaning, pipeline startup and blowout may never reach a steady state. In order to simulate the flow system, several transient two-phase flow simulators have been developed in the past. However, these models are based on the two-fluid model approach. They are complicated and time consuming to run since they treat the gas and liquid phase separately in terms of pressure, temperature and velocity. In this paper a new transient two-phase flow model has been developed. In each time step, the two-phase flow regime, liquid holdup and pressure gradient are estimated with the empirical correlations which are well developed for the steadystate flow. A drift-flux equation was introduced to close the system. The model was validated against data collected from the public literature, field operations, and other transient software. Several field cases are used to illustrate the transient nature of pipeline production, underbalanced drilling (UBD), sand cleanout, and liquid unloading. The benefits of using the transient simulation for the operational design, training and job execution are also discussed.