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Unified model for pseudo-slug and churn flows
Aljasser, Mohammad
Aljasser, Mohammad
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Fan, Yilin
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2022
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Abstract
Multiphase flow is a term used to express a flow that deals with two or more immiscible phases. In the oil and gas production system, multiphase flow can occur in the wellbore and pipelines, and gas-liquid two-phase flow is one of the most common ones. The term flow pattern describes the distribution of each phase in the multiphase flow system. The major flow patterns in gas-liquid two-phase flow include segregated flow, intermittent flow, bubbly flow and dispersed bubble flow. Intermittent flow is one of the most common flow patterns that occurs in the oil and gas wellbore and pipeline system. For horizontal or inclined pipes, intermittent flow can be further classified into plug flow, slug flow, and pseudo-slug flow. For vertical or near vertical pipe, intermittent flow can be classified into slug flow and churn flow. The focus of this study will be on the two least studied flow patterns namely pseudo-slug and churn flows.
Pseudo-slug and churn flows are generally considered as two different flow patterns because of their visual differences. However, some recent experimental studies have shown that they share many similarities. For example, they both have gas penetration through the slug body; they both locate between slug and segregated flow in the flow pattern map; they demonstrate similar time trace signals of liquid holdup equivalent and distribution histogram; their structure velocities are smaller than the one for conventional slug flow. According to the observation from previous experimental studies, we anticipate that pseudo-slug flow gradually changes to churn flow when the inclination angle changes from horizontal to vertical.
In this study, we developed a simplified unified hydraulic model for pseudo-slug and churn flows, that captures the effects of inclination angle, gas and liquid flow rates, and fluid properties, such as liquid viscosity and gas density, on the liquid holdup and pressure gradient. It removes the need for the user to switch the models as the flow pattern (or inclination angle) changes. The
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liquid holdup is predicted using the drift-flux model concept, with new correlations for the drift velocity and flow distribution coefficient. The pressure gradient is predicted using two-fluid model with modified gas and liquid shear stresses by considering the additional shear induced by the “huge wave” structures and the oscillated nature of the liquid film caused by gravity. The model gives the best predictions as compared with other available models in the literature, in terms of predictions for pseudo-slug flow solely, churn flow solely, and both flow patterns.
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