Hole Cleaning Evaluation Of Extended-Reach Wells Under The Condition Of Drill String Rotation

In order to solve the problem of the higher string friction and pipe-sticking caused by rock cuttings deposition in the extended-reach horizontal wells,we have paid much attention to doing the research on the rule of cutting transportation to prove the well cleaning.The rock cuttings transportation theory models can be divided into two kinds: the critical velocity model and the hierarchical model.The critical velocity model forces on a single rock cutting particle to study the forming process of rock cuttings bed in wellbore,then by calculating the critical carrying rock annular velocity,the position that contributing to forming rock cuttings bed can be predicted.Critical velocity model provide a direct and effective way to judge the well bore is whether clean or not.Hierarchical model focus on the whore rock cuttings bed to study the rock cuttings bed changing rule under different external forces.Then by calculating the thickness of rock cuttings bed,the hierarchical model can predict external parameters which influence it and let us know the hole cleaning condition.This paper does research on the cuttings migration feature and mechanism in the extended-reach wells through the way of stress analyzing and influencing factors analyzing.Meanwhile this paper revises cuttings particle point location in the towing force,establishes critical velocity prediction method in the eccentric annulus.This method considers the form of borehole,the condition of drilling,drilling fluid properties and the state of drill string influencing the critical velocity;By using the solid liquid two phase flow theory,this paper also establishes a new three layers of rock cuttings migration unstable model,considering the effect of the drill string rotation.Then solve the model and analyze the results.