A Three-Layer Modeling for Cuttings Transport with Coiled Tubing Horizontal Drilling

A new approach of three-layer flow of two-phase (solid-liquid) fluid in annulus, i.e. a stationary bed of drilled cuttings at bottom; a moving bed layer above it; and a heterogeneous suspension layer at the top, is proposed to predict and interpret the cuttings transport mechanism. This new mathematical model is presented to overcome the limitation in the existing two-layer models. This enables efficient prediction of cuttings transport during horizontal drilling using coiled tubing. In particular, the model described in this paper formulates transport process and includes the relevant parameters such as rheological characteristics of the drilling fluid, cuttings size/sphericity/ concentration, wellbore geometry, eccentricity of the coiled tubing, and pumping rate of the drilling fluid. This paper presents the model development, solution, and simulation of the cutting transport process to illustrate the steps involved in determining the effect of each parameter during the drilling operation. Graphical charts and developed correlations between annular flow rate, rheology, wellbore geometry, eccentricity, cuttings size and concentration in each layer, and the carrying capacity are also presented. The simulation results show how to obtain a reasonable pumping velocity of drilling fluid with the possible lowest pressure gradient that might serve as an operational guideline during drilling. Furthermore, the effects of parameters affecting the efficiency of cutting transport are discussed. These results are compared with published experimental data. The observed agreement and discrepancies are discussed, and further improvements on the current model are proposed.