This paper presents a simplified model for gas-liquid two-phase flow in churn and annular flow regimes for small- and large-diameter near-vertical pipes. Churn flow is considered by many investigators as the least understood flow regime in upward gas-liquid flow in vertical pipes. Nevertheless, this flow regime is commonly found in several applications in the oil and gas industry, such as in gas-lift operations, production of gas-condensate wells, and high-gas-volume fraction two-phase flows in general. In addition to that, the accuracy of two-phase flow models for large pipe diameters, irrespective of flow regimes, is still questionable. Only a few studies can be found in the open literature that validate two-phase flow models for pipe diameters larger than 0.20 m (8 in).
The model developed in the present study is based on an approach originally proposed by previous studies for flows in churn and annular flow regimes for pipe diameters smaller than 0.0254 m (2 in). A simplification of the phase distribution in the churn flow regime is applied in this study such that there is a liquid film flowing upwards (representing net liquid flow rate) on the pipe wall and a gas core, similar to that in the annular flow regime. This model is validated with field and laboratory experimental data from several different studies from the literature, in terms of pressure-gradient and liquid holdup results, for pipe diameters ranging from 0.0254 to 0.279 m (1 to 11 in). Other widely accepted models and commercial packages are also compared with the model proposed in this study.
The comparison between experimental data and this new model shows that this model has an overall better performance than the other models widely used in the oil and gas industry. In addition to that, the proposed model in this study also captures the trend of pressure gradient and liquid holdup better than the other models.
Gas-liquid two-phase flow is widely existent in many industrial areas. In the chemical processing industry, two-phase flow is encountered easily in several types of equipment. For instance, distillation towers and direct contact heat exchangers. The nuclear power industry makes use of steam and water two-phase flows, where the fluid mixture works as a coolant to absorb heat from the reactor core. In the petroleum industry, gas-liquid two-phase flow occurs inside wellbores, risers and pipelines, during production and transportation of hydrocarbons.