Numerical simulation of slug flow in pipelines using drift flux constitutive equations for gas-viscous oil two-phase flow.

Transient simulation of multiphase flow in pipes has been performed using Two-Fluid Model and Drift-Flux Model. The main advantage of the Drift-Flux Model is the reduced number of differential equations, which results in a lower computational time. However, the accuracy of the model depends on a suitable constitutive equation for the velocity of the dispersed phase, commonly, the gas phase. The gas velocity constitutive equation includes two important parameters, namely, the distribution coefficient and the void-fraction-weighted drift velocity. A drift-flux-model code was developed, by using the Finite Volume Method (FVM) with staggered grid system, to evaluate the effect of highly viscous liquid and pipe geometry (pipe diameter and pipe inclination) in the prediction of liquid hold-up and pressure drop gradient. The gas phase compressibility was also included in the model. The results show that the energy consumption to pump the fluids through the lift system has been overestimated when highly viscous liquids are produced. For the case of a vertical upward flow, the overestimation can be up to 10 % of energy consumption. We strongly recommend incorporating the effects of pipe inclination and liquid viscosity into the estimation of the Distribution Coefficient of the dispersed phase, encompassing both and gas drift velocity.