Effective hole cleaning is an important task in directional and/or horizontal well drilling. Inadequate hole cleaning can lead to severe problems such as; stuck pipe, high rotary torque, low penetration rate and cutting bed formation which may lead to micro channel formation.

It is well known that for the same drilling conditions the directional wells require significantly higher flow rates than that of vertical ones in order to obtain the same cleaning efficiency. However, for many cases the required flow rates are not practically achievable due to pump limitations and/or borehole washouts.

Determining cutting carrying capacity by assuming concentric annulus is far from realistic for horizontal and deviated wells as the pipes have a tendency to lay on the low side of the hole under the influence of gravity. Therefore, it becomes necessary to develop a design model for drilling fluid carrying capacity for directional wells taking into consideration the actual mechanism of cutting transport through an inclined eccentric annulus.

A new design model for cutting carrying capacity for directional wells has been developed in this study by taking into consideration the non-Newtonian flow through an inclined eccentric annulus for both laminar and turbulent flow regimes. The proposed method calls for the determination of four different flow rates. The first one is the minimum flow rate required to ensure the flow occurs through the entire eccentric annulus (i.e., there is no stagnant fluid). The second one is the critical flow rate below which the pipe may get stuck due to cutting bed formation. The third one is the minimum rate above which the particles are not able to segregate and form steady bed. The fourth one is the optimum flow rate, which minimizes the bottom hole hydrodynamic pressure. Then these flow rates are compared with each other in order to obtain the recommended flow rate for a given drilling condition.

You can access this article if you purchase or spend a download.