Title: A Three-Layer Modeling for Cuttings Transport in Coiled Tubing Horizontal Drilling
Author(s): Hyun Cho and Subhash N. Shah, Well Construction Technology Center, The University of Oklahoma
Presentation: 2000 SPE Annual Technical Conference and Exhibition
Location: Dallas, Texas USA
Date: October 01-04, 2000
Abstract: A new mathematical model is presented in order to overcome the limitation in the existing two layer models. This enables efficient prediction of cutting transport in coiled tubing horizontal drilling. A new approach of three-layer flow under two phase flow in annulus; 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 cutting transport mechanism. In particular, the model described in this paper formulates transport process and includes the relevant parameters such as rheological characteristics of the drilling fluid, cutting size/sphericity/concentration, wellbore geometry, eccentricity of the coiled tubing, and pumping rate of 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 correlation between annular flow rate, rheology, wellbore geometry, eccentricity, cutting 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. Moreover, the effects of parameters that affect 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.