Simulation Study On Dynamic Mechanical Behavior Of Large Inclined Well Overhaul Pipe String

With the pervasive application of highly-deviated well technology in oilfield, it makes workover operation more difficult. Due to the characteristics of high deviation angle and the long horizontal displacement in highly-deviated well, the transfer efficiency of axial force and the torque is much lower than that in vertical well. Meanwhile, the small diameter and low stiffness increase the risk of workover operation. So understanding of workover string dynamics plays an important role in improving the workover efficiency, ensuring the safety and lowing the cost.In this paper, on the basis of previous studies, the points discussed not enough about the workover string dynamics are studied using the experiment and simulation method. The relationship between WOB (Weight of Bit) and torque of workover tools is analyzed according to the laboratory test. The simulation model of string and deviated wellbore is established and it was verified by the oilfield experiment. And the parameter sensitivity of the string dynamics is studied through the simulation method. While the investigations into workover string dynamics in different field workover operations are simulated in highly deviated well. It provides the suggestions about the string combination and the scope of WOB. The main research works are as follows.First of all, the modeling method of dynamic behavior on workover string is studied. According to the contact characteristics between workover string and wellbore, the contact model and contact algorithm are analyzed. Using the theory of ocean wave mechanics, the viscous damping model is established to descript the interaction between workover string and fluid. Combining the bench test, the WOB-Torque models of workover tools are developed in the workover operation. And the finite model was verified by the hoisting and lowering experiment.Then, a research about the parameter sensitivity of workover string is conducted. The factor of hoisting and lowering's velocity is analyzed and the results show that the axial force will increase with the hoisting velocity. The factors of deviation angle, build-up rate and hook load are studied on the axial force and torque. And quantitative analysis of effect degree in different factors have been carried out through the loss of axial force and torque per 100 meter. And the friction coefficient, string wall's thickness and the annual clearance are researched to discuss the effect on critical buckling load, the results of which show that the increase of the friction coefficient and the decrease of clearance will increase the critical buckling load.Last but not least, different workover operation is simulated to study the workover string dynamics. The load characteristics in hoisting and lowering operation are investigated. The results show that the contact force during hoisting is larger than that in lowering operation, and the loss of axial force per 100 meter, in the first build-up section, is the maximum. Also, this paper has an analysis of the packer releasing operation, and the simulation hook load are compared with the experiment hook load and the hook load in vertical well. The washover and milling operation are simulated through the established model, and a program is improved to set the stabilizer and drill collar. Meanwhile, the critical WOB is analyzed.On the basis of above studies, a secondary development analysis module is developed about the workover string dynamics in highly-deviated well, which is advantageous to the field engineers to master the finite element method and lower the using threshold.