Flow patterns and minimum suspension velocity for efficient cuttings transport in horizontal and deviated wells in coiled-tubing drilling

Coiled-tubing drilling (CTD), which has grown significantly in recent years, is normally associated with high-angle to horizontal and extended-reach wells. In these applications, however, hole problems become more troublesome because of inefficient cuttings removal. Among the many parameters affecting efficient cuttings transport in CTD are pump rates, well dimensions, fluid properties, solid sizes, solid loading, and hole inclination. Several attempts have been made to determine the optimum operating range of these parameters, but complete and satisfactory models have yet to be developed. The purpose of this paper is as follows: To provide a critical review of the state-of-the-art modeling for efficient cuttings transport during CTD. To present the critical parameters involved. To establish their range according to what is observed in practice. To propose a different approach for predicting the minimum suspension velocity. To describe the laboratory system that has been set up. The primary purpose of the flow system is to enable the gathering and publication of good-quality data that, together with previously published data, could further enhance our understanding of the flow of solid/liquid mixtures in annuli.