Study on three-layer unsteady model of cuttings transport for extended-reach well

Hole cleaning is one of the key technologies in extended-reach drilling, the core of which is cuttings transport research. Based on the three-layer steady cuttings transport model of inclined section and two-layer unsteady model developed, a three-layer unsteady cuttings transport model for all sections of ERW is developed and the mechanisms of suspension, rolling and sliding of cuttings, the relative velocity between solid and liquid in suspension layer and the effect of drillpipe rotation are all taken into account. The SETS method is used to solve the model in numerical solution. And the process of solution is described in details. The problem caused by the assumption of fixed bit location, which is inconsistent with the actual drilling, is solved by simulation of dynamic well bottom using virtual grid. The model can be used for calculation and simulation of all sections and processes in actual drilling and well flushing conditions.