Transient Hole Cleaning Behaviour: What Can We Learn From Flow Loop Experiments

Ensuring adequate hole cleaning is important for safe, efficient and economic drilling operations. Most models and flow loop experiments assume steady-state conditions. However, drilling is an inherently transient process. Even in the steadiest situation, the drill bit position advances continuously. When inserting a new stand of drill-pipe there are transients in both string rotation speed and flow rate. Additional transients occur when the drill-pipe is rotated and reciprocated to clean the wellbore. When drilling wells with a narrow pressure margin it is important to control and limit such pressure peaks. We have conducted flow loop experiments in a drilling fluid rig with a 10 m long inclinable test section to investigate hole cleaning performance of field applied oil-based and water-based drilling fluids. While the focus of the experiments has been on steady-state performance, the experiments also provide quantitative information about transient performance. Such information can be used for model closure development. Field applications could include analysis of transient responses from Along-String Measurement instruments, and thus provide additional information on cuttings accumulation, both with respect to location and quantity. Transient data have been analysed using simple physics-based models. We have shown that the pressure peak due to onset of string rotation can be correlated with the cuttings entrainment rate. We further showed that a large fraction of the cuttings can be transported in suspended mode, even for laminar flow without string rotation.