The Force Analysis And Numerical Simulation Of Casing In Full Casing Drilling Method

The paper researched mainly deformation and fracture of casing joint and taper pinfell off from casing joint. We can’t find some literature which analyzed this questiontheoretically at home and abroad. This restricted the use and development of full casingdrilling machine and full casing method.The paper researched the force of casing in drilling, and conducted numericalsimulation of theΦ1200casing and casing joint. Firstly, the paper analyzed force of casing:(1)the weight of casing G;(2)driving torque when casing rotating T1;(3)down force whencasing rotating F;(4) resistance of the casing end N;(5)normal force which soil applied toinner and outer walls of casing FN1,FN2;(6)the friction which soil applied to inner andouter walls Ff1,Ff2;(7) resistance moment of casing shoe T2; According to the theory ofstatic pressure pile, the buried depth of the casing string is divided into three sections: L1（0.3L）、L2(0.6L)、L3(0.1L)(L is the total length of casing string). According to the theoryof static pressure pile, the paper calculated the forces with amended formula in sinkingand pulling the casing string in a Beijing project. And then, the stress state at any sectionis analyzed in elastic-plastic theory. We calculated equivalent stress of L1,L2and L3usingthe fourth strength theory. And then we can get the graph of equivalent stress. Theyshowed that the equivalent stress of L1is almost the same; the equivalent stress of L2isdecrease with the increase of depth, and when the depth is20m, the equivalent stress isminimum. That is to say,20m is demarcation of L1and L2.The equivalent stress of L3isincrease with the depth. It verified the failure position of casing string: the junction of L1and L2, or1/3length of casing string.The paper uses ANSYS simulating force condition of casing string in the projectionof a Beijing projection. We built casing model, and analyzed equivalent stress nephogramof casing string and casing joint. They showed us that (1) casing string is uniformlyforced and there is no phenomenon of stress concentration. The equivalent stress ofcasing is much smaller than its material strength. So casing string don’t destroy in thebody of casing.(2) there is phenomenon of stress concentration in casing joint, and thestress of casing joint increased sharply. Therefore, it tested that casing string offen destroy at casing joint in the actual situation. The paper conducted numerical simulation of theΦ800andΦ1500casing and casing joint. It is found that the diameter of casing isinversely proportion to the maximum equivalent stress, but the casing stress is notchanging in a linear fashion. Therefore, casing can work well when it bore larger torque.