Multiphase technology is improving everyday in order to provide solutions for even most difficult design problems in most aspects of engineering. In drilling engineering, two-phase flow occurs during underbalanced drilling operations, especially in multilateral and extended reach wells. It has been a challenge for years to identify the flow patterns and predict the frictional pressure losses through circular pipes. Even less is known for annular geometries. In this study, a mechanistic model is developed in order to determine the frictional pressure losses occurring during flow through horizontal eccentric annular conduit. The flow pattern maps and estimated frictional pressure losses using the model are compared with experimental data gathered at METU-PETE-CTFL multiphase flow loop. The results show that model can accurately predict the flow pattern and frictional pressure losses for eccentric annulus. It is also observed that, the flow pattern boundaries for annular geometries differ from those for pipes having same hydraulic diameter.


The investigation of the physics of multiphase flow started at 1950's. Since then, several theoretical and experimental studies have been carried out due to the importance and widely use of multiphase flow. This complicated phenomenon has been well understood for pipe flow. However there are still questions about the applicability of the hydraulic or equivalent diameter approach for flow of two-phase flowing in annular geometry. As the evolutionary history of multiphase flow is investigated, most of the studies carried out inherited the liquid holdup definition of Lockhart and Martinelli[1] and the flow pattern transition equations proposed by Taitel and Dukler[2] and Barnea.[3] Comprehensive and unified two-phase flow models are developed for pipe flow, i.e., Xiao et al.[4] and Petalas and Aziz.[5] Sunthankar,[6] Lage et al.,[7] and Zhou[8] carried out experimental and theoretical studies of two-phase flow in horizontal annulus. A detailed literature review can be found in ref. 9. This study attempts to propose a mechanistic mathematical model developed for two-pahse flow through horizontal fully eccentric annulus. Flow pattern identification and frictional pressure loss determination procedures are presented accordingly. The performance of the model is compared with the experimental data collected from METU-PETE-CTFL multiphase flow loop.


Major concern in mechanistic modeling is the determination of flow patterns accurately. Most of the studies carried out inherited the flow pattern transition definitions proposed by Taitel and Dukler[2] and Barnea.[3] The accurate mapping of the flow patterns is the first step for determination of the frictional pressure losses correctly.

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