| The single cone bit is widely used in deep well and slim hole drilling because of its small impact load in the drilling process and long bearing life.However,the spherical single cone bit which is widely used in the oil field,its tooth attrition and fracture is serious when the bit drilling into the hard and high abrasive formation,which resulting in lower life expectancy.The non-spherical single cone bit which was designed in recent years has made improvements in tooth wear,but it has a greater lateral force in the drilling process,and the eccentric wear of bits is more serious.In order to overcome these defects of single cone bits,this paper designs a new type of single cone bit with the rock-breaking characteristics of single cone bits and PDC bits,and carries out the study of the bench test and the numerical simulation of its drilling process,The details are as follows:(1)In this paper,the structure and performance characteristics of single cone bit are expounded.The geometrical basic equation and failure forms of single cone bit are introduced in detail.The influence of formation characteristics,drilling pressure and speed on drilling of the single cone bit is analyzed.(2)Considering the permeability of the formation,the pore pressure variation of the near-bottom formation in the drilling process of single cone bits are studied.Then,basing on the theory of seepage mechanics,the differential equation is established and the pore pressure distribution is obtained.The mathematical model of the single tooth rock breaking of single cone bit for different permeability reservoirs was established under the condition of fully considering the stress at the bottom of the well,and the application analysis was carried out.The results show that:1)In Low permeability formations,the drilling fluid column pressure and pore pressure have little effect on tooth drilling.2)Compared with low permeability formations,tooth drilling is more sensitive to the change of vertical load in high permeability formations.Therefore,in the higher permeability of the formation,increasing the vertical load of the teeth can effectively improve the drill bit rock breaking efficiency.3)Compared to the low permeability formation,when the formation permeability is high,reducing the nominal pressure difference is more helpful to improve the drilling speed.(3)Based on the existing design principle of single cone bit structure,this paper has improved the existing structure of the tooth and cone,and designed a hybrid single cone bit.(4)This paper designs the bench experiment and measures the axial force,lateral force,footage displacement and rock crushing of the hybrid,spherical and non-spherical single cone bit,then compares and analyzes these parameters of the three bits.The results show that the hybrid single cone bit has lower lateral force than other bits,whose drilling stability is better than that of the non-spherical single cone bit and drilling speed is higher than that of the spherical single cone.(5)Bit-rock interactional model of the hybrid single cone bit are established and drilling processes are simulated.The reliability of the numerical simulation is verified by comparing the drilling time-history curve and footage of the experiment and simulation.Through the comparison of experimental and simulation data,the bottom-hole pattern of the hybrid single cone bit is analyzed in detail,and the movement of the tooth is preliminarily recognized.Then,analyzing the main cutting load of each tooth and its changes with the drilling pressure based on the simulation data.Concluded that the PDC teeth located at the inner edge of the palm and the teeth located at the big end of the cone are the main cutting parts,and the maximum tooth load appears at the big end of the cone.The experimental and numerical simulation results show that the design of the hybrid single cone bit is reasonable,the rock breaking efficiency of the drill bit is improved and the lateral force has been improved compared to the non-spherical single cone bit. |
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