| Although there are theoretical and numerical approaches being used for hydraulics calculations and simulations of cuttings transport in narrow annuli, recent developments in drilling technology such as casing and liner drilling, and more recently, steerable liner drilling techniques, have necessitated experimental studies in this area. The steerable liner drilling technique provides some potential advantages, like shorter operational time, reduced circulation losses, and enhanced borehole strength and stability. On the other hand, there are some drawbacks, such as potentially high annular velocities causing excessive pressure losses as well as possible wellbore washouts. This situation requires optimization of drilling parameters. From this standpoint, a better understanding of hydraulics and cuttings transport in narrow annuli has to be developed.;Experimental work on hydraulics and cuttings transport in narrow annuli has been performed using water and two non-Newtonian fluids at various rotational speeds, flow rates, ROPs and inclination angles. Zhang's (2015) model is applicable to a narrow annulus, with some modifications for pressure drop calculations. The model can be used directly for cuttings concentration estimations, based on experimental results and observations. There exists a fluid velocity value at which the cuttings can be transported effectively with a pressure drop that is relatively low. However, this flow rate number depends on the drilling conditions, and needs to be determined using the correction factor provided by the model. At a particular fluid velocity in the annulus, cuttings concentrations seem to be similar when conventional and narrow annuli are compared, but the pressure drops are significantly different.;Therefore, a modified version Zhang's model can be used as an optimization tool to adjust the flow rate to be diverted in order to ensure effective cuttings transport between the liner and the wellbore section, meanwhile maintain a low frictional pressure loss. |
