During a drilling operation, a real-time analysis of surface and downhole measurements can give indications of poor hole cleaning. However, it is not always intuitive to understand how and where the cuttings are settling in the borehole because the transportation of cuttings and the formation of cuttings beds are largely influenced by the series of actions performed during the operation. With a transient cuttings-transport model, it is possible to get a continuously updated prognosis of the distribution of cuttings in suspension and in beds along the annulus. This information can be of prime importance for making decisions to deal with and prevent poor hole-cleaning conditions.A transient cuttings-transport model has been obtained by integrating closure laws for cuttings transport into a transient drilling model that accounts for both fluid transport and drillstring mechanics.This paper presents how this model was used to monitor two different drilling operations in the North Sea: one using conventional drilling and one using managed-pressure drilling (MPD). Some unknown parameters within the model (e.g., the size of the cuttings particles) were calibrated to obtain a better match with the top-side measurements (cuttings-flow rate, active pit reduction as a result of cuttings removal). With the calibrated model, the prediction of cuttings-bed locations was confirmed by actual drilling incidents such as packoffs and overpulls while tripping out of hole.On the basis of the calibrated transient cuttings-transport model, it is thereby possible to evaluate the adjustments of the drilling parameters that are necessary to stop and possibly remove the cuttings beds, thus giving the drilling team the opportunity to take remedial and preventive actions on the basis of quantitative evaluations, rather than solely on the intuition and experience of the decision makers. IntroductionDuring drilling operations, ensuring proper hole-cleaning conditions is extremely important. Otherwise, serious drilling problems can occur such as stuck-pipe incidents or packoff situations, which can lead to the fracturing of the formation and resulting mud losses. The end result of poor cuttings transport is an increase in nonproductive time. To predict how cuttings are transported, there has been performed a vast amount of experimental work and different attempts on developing appropriate cuttings-transport models. An overview of some of the work that has been performed is given by Pilehvari et al. (1999). It has turned out to be quite complex to describe the cuttings-transport process because transport is influenced by many different parameters such as wellbore geometry, inclination, fluid density, rheology, rate of penetration (ROP), drillstring rotation, flow patterns, flow rate, and cuttings size. One could divide the modeling approach into two

During a drilling operation, real-time analysis of surface and downhole measurements can give indications of poor hole cleaning. However, it is not always intuitive to understand how and where the cuttings are settling in the borehole, because the transportation of cuttings and the formation of cuttings beds are largely influenced by the series of actions performed during the operation. Using a transient cuttings transport model, it is possible to get a continuously updated prognosis of the distribution of cuttings in suspension and in beds along the annulus. This information can be of prime importance for taking decisions to deal with and prevent poor hole cleaning conditions.A transient cuttings transport model has been obtained by integrating closure laws for cuttings transport into a transient drilling model that accounts for both fluid transport and drill-string mechanics.This paper presents how this model was used to monitor two different drilling operations in the North Sea: one using conventional drilling and one using MPD (Managed Pressure Drilling). Some unknown parameters within the model (e.g. the size of the cuttings particles) were calibrated in order to obtain a better match with the top side measurements (cuttings flowrate, active pit reduction due to cuttings removal). Using the calibrated model, the prediction of cuttings bed locations were confirmed by actual drilling incidents like pack-offs and overpulls while tripping out of hole.Based on the calibrated transient cuttings transport model, it is thereby possible to evaluate what adjustments of the drilling parameters are necessary to stop and possibly remove the cuttings beds, therefore giving the drilling team the opportunity to take remedial and preventive actions based on quantitative evaluations, rather than solely upon the intuition and experience of the decision makers.