Predicting Multiphase Flow Behavior in a Deviated Well

Abstract

Summary: In deviated wells of an offshore producing environment, flow of two-or three-phase mixtures is invariably encountered. While many investigators have studied vertical multiphase flow behavior, few studies, often entirely empirical, deal with deviated well systems. The main objective of this work is to present a model that predicts both flow regime and pressure gradient in a deviated wellbore. In the modeling of flow-pattern transition and void fraction, an approach similar to that for vertical flow is taken; i.e., four principal flow regimes are recognized: bubbly, slug, churn, and annular. The transition from bubbly to slug flow is found to be at a local void fraction of 0.25. This transition criterion in terms of gas and liquid superficial velocities is found to be significantly affected by the well deviation, particularly in highly deviated wells. The transitions from slug to chum flow and chum to annular flow occur at high fluid velocities and are unaffected by well deviation. The velocity-profile-distribution parameter for bubbly, slug, and churn flows is found to be unaffected by the well deviation angle. Similarly, the terminal rise velocity for small bubbles also appears to be insignificantly affected by the well deviation. In contrast, the "Taylor" bubble-rise velocity changes dramatically as deviation angle is increased. Thus, the characters of slug and chum flows in a deviated well differ from those in a vertical well. Data on gas void fraction were obtained both from a 5-in. [127-mm] circular pipe and from annular flow channels for deviation angles up to 32° from the vertical. The validity of the proposed model is demonstrated with these data and with laboratory data from other sources. Several field examples are presented to show the application of the model.