Multi-layer Contact Mechanics Analysis Of Semi Articulated Flexible Drilling Tools

After long-term repeated water flooding in many old oil fields,the water surface area of the oil well is continuously enlarged,and a large amount of remaining oil has been accumulated on both sides of the crack,which seriously affects the production of oil wells.In order to enhance oil recovery,many oil fields began to build ultra short radius horizontal wells on the basis of original oil wells,so as to increase the exploitation of remaining oil.Compared with ordinary horizontal wells,the radius of curvature of ultra short radius horizontal wells is very small,generally not exceeding 4.0m.Therefore,ordinary drilling tools can not meet the drilling requirements of ultra short radius horizontal wells.In recent years,semi articulated flexible drilling tools are widely used in ultra short radius horizontal well drilling technology because of their advantages of being flexible and controlling well trajectory.However,how to ensure the rationality of the load and flexibility transfer rule of semi articulated flexible drilling tools is the key to the success of ultra short radius horizontal well drilling.Firstly,according to the working state of flexible drilling tools in ultra short radius horizontal wells,considering the mechanism problem of semi articulated structure and combining theoretical analysis with numerical simulation to study the modeling method of semi articulated flexible drill pipe so that a mechanical model which can reasonably describe the motion law of semi articulated flexible drill pipe is determined.Then,establishing single-layer contact transient dynamic model of a semi articulated flexible drill pipe in the guide screen tube under different flexibility and carrying out the dynamic analysis,the results show that with the increase of well depth,the torque of semi articulated flexible drill pipe decreases and the axial force increases.With the decrease of flexibility,the bottom torque of semi articulated flexible drill pipe decreases,the axial force increases and the total frictional torque between guide screen and semi articulated flexible drill pipe increases.When the flexibility is the same,with the increase of the angle of the well,the bottom torque of the semi articulated flexible drill pipe decreases,the axial force increases,and the total friction torque between guide screen and semi articulated flexible drill pipe increases.Lastly,establishing multi-layer contact transient dynamic model of a semi articulated flexible drilling assembly under different flexibility and carrying out the dynamic analysis,the results show that with the increase of well depth,the torque of semi articulated flexible drill pipe decreases,the axial force of semi articulated flexible drill pipe increases and the axial force of guidescreen increases.With the decrease of the flexibility,the bottom torque of the semi articulated flexible drill pipe decreases,the bottom axial force of the semi articulated flexible drill pipe increases,the bottom axial force of the guide screen increases,the bottom axial force of the semi articulated flexible drilling increases,the total friction torque of the guide screen and the flexible drill pipe increases and the total friction resistance of the guide screen and the wellbore increases.Carrying out the field tests and comparing the field test value of frictional resistance with that of numerical simulation shows that the two are basically consistent.It verifies the correctness of the multi-layer contact mechanics model and the analysis method of the semi articulated flexible drilling tool.The research results provide reasonable mechanical basis for field construction of ultra short radius horizontal wells.