Hole Cleaning Modelling: What's ‘n’ Got to Do With It?

Abstract

Abstract Efficient hole cleaning is vitally important in the drilling of directional and extended-reach (ERD) wells. In previous works, the importance of fluid velocity/pump output has been emphasised, while in others, the importance of individual fluid rheological parameters has been stressed. Drillpipe eccentricity and rotation directly affect hole cleaning as well. Recent work on particle settling velocity has accelerated the understanding of the behaviour of drilled cuttings in wellbores. This paper presents a new model to the industry, which combines recent developments in the fields of particle settling and rheology. This model provides a useful tool for the planning of hole cleaning for highly deviated wells through the use of Lift Factors under the eccentric drillpipe. Information from deviated wells in the field is used to illustrate the usefulness of this hole cleaning model. Importantly, analysis of the data indicates that fluid ‘n’ factors calculated using the yield-power law [Herschel-Bulkley] rheological model play a greater role in promoting good hole cleaning in ERD wells than has previously been recognised.