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Accurately predicting pressure gradient with inner pipe rotation in concentric or eccentric annuli can provide a theoretical foundation to evaluate equivalent mud weight for avoiding downhole problems caused by overlarge downhole pressure, such as: gas kick, lost circulation, even blowout. Nowadays, many studies were carried out on the basis of theoretical and experimental researches to investigate the laminar helical flow in concentric/eccentric annuli, however, to the best of our knowledge, no simplified model has been reported to predicting pressure gradient (PG) in eccentric annuli with inner pipe rotation for yield-power-law (YPL) fluids. In this paper, a simplified modeling for predicting PG of laminar helical flow in an eccentric annulus with YPL fluids has been established. In addition, the validation of simplified model has been investigated by comparing results with computational fluid dynamic (CFD) simulations, existing experimental measurements and numerical model. Predictions of the simplified model shown good agreement with CFD and experimental results within ±10% error bars for power-law and YPL fluids both in concentric and eccentric annuli.

Simplified modeling of laminar helical flow in eccentric annulus with YPL fluid