Analysis And Experimental Research Of The Buckling Characteristics Of The Rotating Flexible Beam That Compressed In The Horizontal Direction

The flexible drill-string has been frequently used in the works of directional petroleum wells,and the stability of the drill-string directly affects the success of drilling,however,the prediction of the buckling load of the drill-string is always a challenge for the drilling industry.Drill string buckling in the drilling process can lead to serious problems,such as the fatigue damage of the string,the excessive wear of down hole tools,MWD failure,the excessive loss of drill bit,the stick-slip of the drill,the borehole wall instability,the erosion and the low efficiency of drilling,and so on.Therefore,it is important to understand and master the stability and the buckling behavior mechanism of the drill in horizontal wells,to ensure the smooth of drilling process.In this paper,the static buckling behavior and dynamic buckling behavior are analyzed.Research on static buckling behavior: A slight string that under the constraint of a horizontal circular tube is taken as the analysis model,the differential equations about the nonlinear buckling behavior of the constrained tubing string is then established under the consideration of the friction and boundary constraints.The differential quadrature(DQ)method and Newton iteration method are used to solve the governing equations.The sinusoidal buckling critical load and buckling displacement are analyzed under the friction coefficient ranged from 0 to 0.6 and four different boundary constraints.The results from simulation show tha t,in these boundary constraints of simply supported-simply supported(SS-SS),simply supported-clamped(SS-C),clamped-simply supported(C-SS)and clamped-clamped(C-C),the clamped-simply supported constraint should be avoided while the simply supportedclamped constraint is adopted to ease the buckling problems.Besides,gravity aggravates the buckling problem.Analysis of dynamic buckling motion:the flexible string that rotates with pressure in the horizontal circular tube is taken as the analysis model,its dynamic buckling behavior is then described,and the dynamic buckling differential equation is proposed to get the perturbation solution,besides,the sinusoidal and spiral buckling critical load formula of the horizontal drill string is deduced by the energy method and the principle of minimum potential energy.The existing simulation experiment device for horizontal well drilling string dyna mic characteristics is reformed in the laboratory,and the simulation test is conducted,for the research of static buckling and dynamic buckling of the drill string in horizontal wells.The transmission efficiency of axial load in horizontal wells is anal yzed by means of simulation test,and the change trend of the friction resistance of drilling column in horizontal well is obtained.The critical load for the buckling of the drill column is determined by the judgment method of friction resistance incremental acceleration,combining with the experimental data,and then compared with the theoretical calculation value.Through the simulation experiment,the influence of the rotational speed on the dynamic buckling motion is analyzed and the amplitude and the change of axis trajectory of dynamic buckling are observed.It is found that the amplitude of dynamic buckling vibration and vibration frequency increased with the increase of rotational speed;When the rotational speed of the drill string is increased fro m 17 r / min to 107 r / min,the critical load of the spiral buckling is reduced from 86% to 75%;When the rotational speed reaches 107 r / min,if the loading load exceeds the critical buckling of the spiral,the dynamic buckling motion of the drill string will change from snake motion to eddy motion.