Effect of slip Velocity in Multiphase Production from Oil Wells

In multicomponent multiphase (gas/liquid) flow such as flow of hydrocarbons in wellbores; pressure, temperature, composition and liquid holdupdistributions are interrelated. The general method used to calculate composition of each phase is equilibrium flash calculation. In this method, we assume that liquid phase and gas phase are in equilibrium which is not true when these two phases are moving at different velocities. To consider the effect of slip between the phases, the liquid phase is divided into two parts and only one of them is in equilibrium with the gas phase.Then material balance equation is solved using an appropriate holdup correlation. This model is then inserted into a compositional multiphase flow simulator prepared for vertical and deviated oil wells. Simulations are done for real cases from south Iranian oil wells using both approaches. The two models predict different results especially in complex mixture phase behavior such as volatile oils and retrograde condensates. Ability of the nonequilibrium model to update the overall composition at each step makes the predictions of this model more reliable. Using this model in multiphase simulators also helps for a better understanding of composition-dependent phenomena usually involved in wellbores and pipelines.

Keywords:

multiphase flow , slip velocity , holdup , flash calculation , nonequilibrium model