The Drag And Friction Of Completion String In Horizontal Well-Analysis And Prediction

Casing string is composed of some casing from screw joint casing and centering device. The length of any one of casing is about 10 meters. The casing string is one of downhole string. From the 60s, many scholars from domestic or abroad have carried out the theoretical and experimental study on drag and deformation of downhole string and obtained a large number of results. The main analysis methods of drag and deformation of downhole string are differential equation method, flexed beam method, weighting constant method, finite difference method and finite element method. The friction prediction is the kind point of the analysis of drag and deformation, because friction is the key element of casing running design and running in. Before running casing string, we must calculate drag in wellbore and make the feasibility analysis of running casing string. Now, the model for computing the drag of casing string belongs to drill pipe model. There is no special model for calculation the drag. We use the drill pipe model for computing the drag of casing string, which have neglected the torque and rotation speed.The focus of this paper is established the drag differential equation and finite element equation of casing string in three-dime horizontal hole under appropriate assumptions and neglect. From calculation, we can conclude: In wellbore, when we ignore the affection of drilling fluid, casing string structure and borehole face, the curvilinear trend of friction is consistent with curvilinear trend of rate of over all angle change. If any factor can impact the rate of over all angle change, it can impact the friction. With deviation angle increase, the friction is also increasing. But in horizontal hole section, friction fluctuates in small scope. In horizontal well, frontal side casing string is usual bearing pressure. In horizontal hole section, with the length of casing increase, the hook load is decreasing on the contrary. The calculation results of the two mthods have different numerical value, but the curvilinear trend of results are consistent. The finite element method can calculate the transversal displacement of casing. From this we can compute gun to casing clearance, which can instruct the arrangement centering device on theory.