Experimental and Theoretical Studies on Taylor Bubbles Rising in Stagnant Non-Newtonian Fluids in Inclined Non-Concentric Annuli

Abstract

Experiments have been conducted measuring the drift velocity (Ud) of single Taylor bubbles rising in stagnant Bingham plastic fluids in an inclined (4° ≤θ≤ 45° from vertical) and fully eccentric 0.1524 × 0.1016-m (6 × 4-in) annulus. The results presented contribute to addressing the knowledge gap of how Taylor bubbles migrate through water-based fluids used in the process of drilling oil, gas and geothermal wells. The experimental results indicate that for all fluids tested,(1) Ud is generally maximized at an inclination angle (θ) of ∼30o,(2) Ud decreases with increasing plastic viscosity (μp) and yield point (τy),(3) Ud decreases when rotating the inner pipe of the annulus at a commonly used drilling operation speed of 100 rpm and(4) Ud is unaffected by the length of the Taylor bubble (LTB).It was also observed that LTB decreases as μp and τyincrease, and that pipe rotation has no effect on LTB.The characteristic dimension (D*), used in determining both the Froude number (Frθ) and apparent viscosity (μapp), has been selected as (Do+Di). These, inclination angle (θ), and experimental results from this and other studies form the basis for developing a drift velocity correlation. Additionally, a theoretical model applying a slot-flow approach is developed for predicting bubble rise velocities for both concentric and fully eccentric annuli. The drift velocity predicted from both the theoretical model and the correlation exhibit good agreement with the experimental results of the present work and those reported in literature.