The Stability Analysis Of Bottom Hole Assembly In Vertical Wells

In the process of drilling,the drilling efficiency can be improved by properly increasing the weight on bit.Commonly used drilling pressure is greater than critical drilling pressure of drill collar,To improve the efficiency of drilling,centralizer and the big drill collar should be used to improve the stability of the Bottom Hole Assembly(BHA).So This article was writed based on predecessors' study.First,The introduction part of the article describes the current situation and common methods study abroad BHA stability,By comparing the advantages and disadvantages of each method,theoretical content of this article was selected and was set forth in the Chapter II,Chapter III.The second chapter analyzes the BHA reasonable working conditions,boundary conditions is assumed,mechanical model is established.Based on the mechanical model,the flexing equation is established by the bending equation and force vector equilibrium.Bessel function method is used to answer both ends hinged of the BHA's critical WOB mathematical expression.Meanwhile according to Euler strut model and BHA's deformation energy equation and the principle of minimum potential energy,the both ends fixed of the BHA's critical WOB mathematical expression is established.On this basis,the BHA mathematical expression critical WOB is expanded with centralizer,but both methods are more simplified conditions and the results are large deviation.It only can be used as special conditions theory answer.Chapter III is based on the finite element model of the space beam element,gap element is introduced,BHA is derived finite element formulation of nonlinear buckling.In the theoretical derivation,the contact state discriminant is confirmed based on the gap element and dirll collar and the wall and its relationship.Second,Eigenvalues buckling and nonlinear buckling is used to simulate the BHA's buckling mode by the ANSYS software provided in chapter IV.The article outlined the principles of the eigenvalues and nonlinear buckling.selected PIPE16 to model and verify the reliability.On this basis,elaborated in full and part-bound constraints under two working conditions,unit force and gravity are two basic methods from loading simulation the BHA stability.AT last,Through six examples four group BHAs the buckling modes,critical WOB,maximum flexion displacement position,the maximum displacement,displacement bifurcation,bifurcation point load was discussed.then ascertain the impact of centralizer placed the number,location and drill collars combination of WOB.Provide a reference for drilling operations.