Transport of Cuttings in Directional Wells

Abstract

The aim of this research is to define easily applicable quantitative relationships for optimizing flow rates and drilling-fluid rheology depending on the inclination of the well. The research project involves various aspects: (1) laboratory experiments, (2) experiments in wells during drilling, (3) building a numerical model based on experimental data obtained in both the laboratory and wells.Laboratory experiments performed in tubes and annular-space models have analyzed the influence of various parameters such as inclination, rotation of the drill string and fluid rheology, including thixotropy. The results of these experiments have led to equations describing the minimum fluid velocity required for evacuating cuttings versus their density, the density of the fluid and its rheological properties. In the numerical model, with a view to applying these equations to the well, they have been adjusted with the help of results obtained by checking the arrival of cuttings at the drill site during the drilling out of hardened cement in the casing above the casing shoe after cementing jobs.Among the conslusions reached, the following points can be noted:The influence of inclination becomes apparent as soon as the well becomes slightly deviated (10°).Evacuation of cuttings is more difficult in slanting zones, depending on the case, with an angle between 30 and 60°.High viscosity of the drilling fluid is favorable for the cleaning of the well in the nearly vertical part but may reduce the transfer capacity in the slanting parts.High thixotropy of the drilling fluid is very unfavorable in the slanting parts, especially if the rotation speed of the drill string is low.The increase in the density of the drilling fluid facilitates transport.