Effect of Mud Rheology on Cuttings' Transport in Drilling Operations

Abstract

Settling of solid particles in drilling fluids represents a major problem, necessitating effective removal of drilled cuttings to the surface of the well to maintain safe and profitable drilling operations. Experiments were conducted using two group of drilling fluids, Newtonian (water, gas-oil, kerosene, and ethyl-glycol) and Non-Newtonian (Carboxyl Methyl cellulose (CMC)) in four different concentrations. Four cutting sizes were used, with diameters 0.212, 0.445, 0.672, and 0.853 cm, taken from the Garraf area of the Nasirya oil fields. The test results showed lower Reynolds numbers within the laminar flow region compared with the Turbulent flow region. The drag coefficients decreased with increasing particle Reynolds number, and small particle sizes gave higher drag coefficients and lower Reynolds numbers, while large particles gave lower drag coefficients and higher Reynolds numbers in both Newtonian and Non-Newtonian fluids. The results indicate that an increase in CMC concentration will decrease NRep and increase the drag coefficient for different particle sizes. For non-Newtonian fluids, the settling velocity decreases with increases in CMC concentration due to increases in the viscous forces that oppose settling of particles, while in Newtonian fluids, the settling velocity increases with increasing particle size due to gravity forces increasing. The low CMC concentrations (low n, and high k) offer higher settling velocities, while larger particle sizes give lower drag coefficients than smaller ones.