Study On The Influence Of Window Side Drilling Process On Cement Ring Cement Strength And Production Casing Strength

The function of window sidetracking technology is to restore the production efficiency of various oil wells and effectively reduce the comprehensive development cost of oil fields.At this stage,in order to ensure the safety of sidetracking new wells,new casings are often suspended at 20m～30m above the sidetracking point of the window,and the lengthening of the suspension position has caused great waste of casing.The high suspension of the new casing is mainly due to the failure of the cement ring and its cementation surface after sidetracking and the residual strength of the casing cannot be determined,so that the safety of sidetracking can only be ensured by lengthening the suspension.Aiming at this problem,this paper takes the casing-cement sheath-formation combination system as the research object,and studies the dynamic response of the window sidetracking process.The specific research work is as follows :(1)According to the window sidetracking data of an oil well,the structural parameters and load parameters of casing and cement sheath under cementing condition are obtained.The calculation methods of cement sheath cementation surface simulation and load transfer are described in detail.Based on the initial cementation strength of cement sheath under cementing condition,the evaluation method of cement sheath cementation strength is proposed.By comparing with the theoretical calculation results,the accuracy of load transfer of casing-cement sheath-formation combination system established in this paper is verified.Based on the fourth strength theory and internal pressure coefficient,the evaluation method of casing strength and residual strength is obtained.(2)Considering the stress state of the casing during the window sidetracking process,based on the impact load of milling cone milling,the augmented Lagrangian matrix is promoted,and the Lagrangian method of the combined system based on the impact effect is established.This method can describe the balance between contact force and energy,ensure the appropriate transfer of linear momentum,and ensure that the milling casing will cause continuous impact on the cemented surface.Furthermore,the harmonic motion equation based on the damping matrix is obtained,which can fully consider the response characteristics of the combined system under the action of periodic drilling pressure.(3)Through the analysis of the basic working conditions,the failure range of the cement sheath and its cementation surface,and the change of the cementation strength of the first and second cementation surfaces of the cement sheath during the sidetracking process are obtained.The response and damage of different pump pressures and different cement ring thickness to periodic drilling pressure are compared and analyzed.The results show that the larger the pump pressure,the larger the damage range of the cement sheath and the larger the failure range of the cement sheath cementation surface;the thicker the cement sheath,the larger the failure range of the cement sheath,and the larger the failure range of the cement sheath cementation surface.(4)Through the analysis of the dynamic response characteristics of the casing string in the process of window sidetracking under given well conditions,the response state of the casing string in the process of window sidetracking is obtained,and the residual strength of the casing under given well conditions is analyzed to obtain the failure range of the casing.The response and failure of different pump pressures and different cement rings to periodic drilling pressure are compared and analyzed.The results show that the larger the pump pressure,the larger the failure range of the casing.The thicker the cement sheath,the greater the failure range of the casing.In this paper,the structural response and failure influencing factors of casing-cement sheath-formation combined system under periodic WOB under different working conditions are calculated and analyzed,so as to provide reference for casing suspension position,reduce the loss caused by excessive suspension,and strengthen the economy and safety of new casing suspension position.