A New Computer Package for Simulating Cuttings Transport and Predicting Hole Cleaning in Deviated and Horizontal Wells
Authors: Zou Longqing , Patel M.H. , Han Guoyou 
Published: December 2007

A computer package, HCPT, which has been developed provides a useful tool for the field engineer to make prediction and analysis of the drilled cuttings transport in drilling inclined well to assure efficient hole cleaning during operations. It has been designed to allow the user to calculate the cuttings bed formation, determine whether the bed slides upward or remains stationary and analyse the position of the cuttings bed formed and the height of the cuttings bed layer. It has been programmed using Visual Basic and will be performed as an executable file in the Windows system environment.

This user-friendly computer package has been developed on the basis of the theory that authors established. The theory contains a new mathematical model, which enables the simulation and prediction of cuttings transport in highly deviated to horizontal wells taking account of operating parameters, wellbore geometry, fluid properties and cutting characteristics. A three-layer model for cuttings transport and some equations for cuttings concentrations have been included.

Introduction

One of the primary functions of the drilling fluid is the transport of drilled cuttings out of the hole. Over 18 years or so, considerable efforts have been expended on solving this problem in inclined to horizontal wells. The methods by these investigators can be categorized into two main approaches: an empirical1-4 and theoretical5-7. The simulating limitation of those is still existed because of very specific range of operating empirical conditions and based on simplified theory. Therefore, a few mathematical models can only simulate a limited range of phenomena observed in laboratories.

This work has developed a new mathematical model, from which the set of equations are derived and a numerical solution is proposed.

By analyzing the mechanism of cuttings bed formed in inclined wellbore, a three-layer model for cuttings transport has been established, and some relative equations including cuttings bed height and cuttings particle settling velocity have been obtained. They give the method of how to determine when the cuttings bed will be formed and what kind of formed cuttings bed it is.

Considering the situation that drilled cuttings have gone through the different angle hole sections, the cuttings concentration should not be the same in each of hole sections of the inclined well. The equations of cuttings concentration are available.

The motion of the moving bed layer formed in inclined wellbore is controlled by the critical velocity of the moving bed layer, which has been derived from the equation of cuttings bed force balance. In order to accomplish the three fields above, the parameters in annular fluid flow such as flowrate, velocity profile, pressure gradient and apparent viscosity are required. Some equations that have to be numerically solved have been derived from the basic equations of fluid mechanics and boundary conditions.

Model Development

Calculation of the Basic Parameters.

The theoretical models require an accurate description of the rheological properties of the fluid and determination of velocity and apparent viscosity profiles in the annulus of the borehole.

Bingham-Plastic rheological model is as follows:Equation (1)

In order to obtain the velocity profile model for annular fluid at different pipe rotary speeds and pipe eccentricities, some flow equations must be derived from the equations of motion and continuity, and assumptions are made regarding the fluids and boundary conditions.

Calculation of the Basic Parameters.

The theoretical models require an accurate description of the rheological properties of the fluid and determination of velocity and apparent viscosity profiles in the annulus of the borehole.

Bingham-Plastic rheological model is as follows:Equation (1)

In order to obtain the velocity profile model for annular fluid at different pipe rotary speeds and pipe eccentricities, some flow equations must be derived from the equations of motion and continuity, and assumptions are made regarding the fluids and boundary conditions.