Predicting Cuttings Settling Velocity in Drilling Muds and in Rising-Bubbles-Containing Muds

Abstract

Summary The main objectives of this paper are to study the cuttings settling velocity in drilling muds and rising-bubbles-containing muds and to develop a prediction model suitable for both cases. For this purpose, experiments were carried out by using water, glycerine and Carboxymethyl Cellulose (CMC) fluids with different viscosity as drilling muds and aluminum particles as cuttings. Air was used as the gas phase. To ensure the reliability of the tests, the work has been divided into two parts. In the first part, the goodness of the obtained experimental results from gas-free liquids was assessed with the standard drag coefficient curve and the Cheng’s equation. In the second part, the above-mentioned results were compared with those obtained from gas-liquid mixtures under various gas void fraction conditions. Through this work, in addition to the settling velocity calculation procedure of Walker and Mayes, a newly developed model is suggested for predicting cuttings settling velocity applicable for the solid-liquid two–phase flow and solid-liquid-gas three-phase flow. Furthermore, it was found that the bubble-particle collision in viscous fluids resulted in a decrease in cuttings settling velocity by 20% to 50% while the combined effect of the bubble-particle interaction and mixture viscosity and density variation due to the gas phase could increase cuttings settling velocity by two or three times compared with that in gas-free drilling muds. The results also showed that only in water (non-viscous fluid) with a gas volumetric smaller than 7.5% can considerably help to maintain solid particles in suspension, and for more than 7.5% there is increased in settling velocity compare to its value in gas-free water before mitigating at around 20% void fractions and more. The results of this study could provide to the drilling operators additional information on the cuttings slip velocity estimation during gas influx or underbalanced conditions.