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Polycrystalline diamond compact bit has been used in more than 90% drilling length all over the world. Tooth wear is the main factor reducing the service life and performance of the polycrystalline diamond compact bit. In this article, the mechanical properties of polycrystalline diamond compact bit under wearing conditions are studied. The geometric model of the worn and unworn cutters is built. A numerical method to address the cutting parameters of cutters is first proposed. Then the effects of wearing degrees and the penetration per revolution of polycrystalline diamond compact bit on cutting parameters, forces, and wear conditions are discussed. The result shows that the numerical method can be utilized to obtain the force conditions of cutters, predict the wear trends of polycrystalline diamond compact bit, and optimize the cutter layout design. The effect of penetration per revolution on the mechanical properties of polycrystalline diamond compact bit and cutters is very limited. Under a constant penetration per revolution, the cutting section area almost keeps a constant with the increase of wearing degree; the direction of the transverse force keeps unchanged. The force conditions are closely related to cutting arc length and the wear degree.

Based on the bionic non-smooth surface theory, this article carries out (1) design of the structure of bionic non-smooth sealing rings and toothed bars of the sealing structure and (2) finite element simulation study on the bionic non-smooth surface structure of roller-cone bits. The result shows that (1) when the parameter Y is equal to the rack angles, the maximum pressure of the Type B is smaller than that of the Type A, while the equivalent stress of the Type A is smaller than that of the Type B; when the parameter Y is equal to the tooth distribution, the maximum pressure and the equivalent stress of the rack angle of 30°are smaller than that of the rack angle of 20°; and when the rack angle is equal to the tooth distribution, the maximum contact pressure and the equivalent stress of the tooth decrease with the increase in the parameter Y.(2) Compared with the O-shaped sealing rings, the new tooth bars avoid the problem of over-large contact area. (3) The grid-shaped sealing structure can increase the wear resistance of rubber rings and delay their wear and aging, thus improving their service life.

Highlights1. A new comprehensive six degrees-of-freedom lump mass model of drill-string suitable for horizontal wells was proposed.2. The models aims to investigate instabilities caused by cutting rock formations and frictional effects within a Bottom Whole Assemble (BHA) and a drill-string. 3.We have observed all types nonlinear effects including stick-slip, bit bounce and whirling.

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