A computational fluid dynamics (CFD) analysis is conducted on the flow of Newtonian and non-Newtonian fluids in annuli including the effect of inner pipe rotation. A practical numerical model is proposed that accurately estimates the annular frictional pressure losses with and without the inner pipe rotation. Experiments are conducted at a 91 ft. long flow loop using various fluids that can be characterized as Yield Power Law (YPL). A commercial CFD software is used to validate the proposed numerical approach. A comprehensive comparison of the proposed model, CFD results, experimental results, the published experimental results and most widely used models from the literature is presented.

The experimental setup simulates horizontal wellbore applications, which are increasingly prevalent due to recent shale plays. Today, since most drilling fluids show YPL behavior, YPL fluids with a wide range of rheological properties are used as test fluids in this study. The numerical model is coupled with a stability criterion that determines the onset and offset of the transitional flow between laminar and turbulent regions. The velocity profiles of a wide range of diameter ratios, Taylor and Reynolds numbers are presented. Various degrees of eccentricity are analyzed in terms of pressure profile and flow stability with the proposed method.

The results from the experiments show significantly reduced pressure drops in fully eccentric annuli compared to concentric geometry. An increase in pressure loss is observed as the pipe is rotated while it is eccentric. The comparisons between the models indicate that the slot approximation can result in large errors especially when the diameter ratio is low. A 3D wellbore can be evaluated with grids using the proposed numerical method and the local stability criterion, which leads to accurate pressure loss estimations. Grid analysis can show the flow state profile and the pressure loss profile of a wellbore, which has potential to optimize operations in real-time or in the design phase.

This study contributes to a better understanding of flow in annuli. The results obtained from this study are useful to predict the transition and the annular frictional pressure loss profiles more accurately than existing methods. Potential applications include risk avoidance and optimized operations.

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