Study On Rock-breaking Technology Of PDC Bit Under Torsional Impactor

With the development of oil and gas resources,there are more deep and ultra-deep wells,with the increase of well depth,stick-slip phenomenon and slow drilling speed are the problems need to be solved to improve the drilling efficiency,which has become a hot topic in the development of oil and gas.A torsional impactor is installed above the drill bit,which produces continuous high frequency and low amplitude circumferential impact force driving by drilling fluid.The torsional impactor transfers and supplies an extra cutting force to the drill bit,so that the drill bit can drill into the rock stratum faster,it will speed up the ROP and improve drilling efficiency.In this paper,the rock-breaking technology of PDC bit under torsional impact is studied.First the theoretical analysis of torsional impact increasing drilling speed,second the dynamics simulation of rock-breaking using PDC bit.Combining theoretical analysis and dynamics simulation,it provides a basis for the application of high rock-breaking speed mechanism using PDC bit after applying torsional impactor.The main works and results of this paper are as follows:(1)The structure of the torsional impactor is introduced according to the four key states.Also,the hydraulic working principle is introduced.According to the principle of conservation of energy,the way to achieve the torque impact is analyzed theoretically.Through the process that the fluid flow from the entrance to the export process,the energy fluid loss must be greater than the impact hammer movement kinetic energy to make it work.(2)The mitigation effect of the circumferential torque impact on the stick slip vibration is analyzed.Based on existing BHA model,the differential equations that drill bit moves in axial and circumferential direction.Form force analysis to PDC bit,axial and circumferential rock-breaking conditions are calculated,and boundary conditions of stick-slip vibration under circumferential torque are obtained.The numerical calculation is carried out through given working conditions,and the comparing under different conditions of PDC bit is made.The results show that the applying a torsional impactor has a good effect on the mitigation of stick-slip vibration.(3)In order to analyze the influence of torque impact on the drilling process in different working conditions more reasonable,the dynamic simulation of the rock-breaking process using PDC bit needs to be carried out.Because of the poor performance of rock material in simulation software,also the shortage of material failure criteria,it is unable to get ideal simulation results.At the same time,in order to fit with the simulation conditions,the UMAT file that defined rock material constitutive is written based on.the plastic failure of rock and D-P model.At last,three axial compression tests for a single element are carried out and the correctness of the UMAT file is verified.(4)Based on the BHA model and UMAT file that defined rock material constitutive,the dynamic simulation of PDC bit rock-breaking process in the LS-DYNA software platform is conducted.The BHA model in section(2)is used for the finite element model in simulation.Reasonable boundary conditions and loading of the finite element model are set,and comparison simulation under multiple group parameters is compared.The rock-breaking process is obtained in different WOB under different torsional impact,which verify the torsional impact can mitigate stick-slip vibration and improve the ROP.Through the analysis above,we have a deeper understanding of rock-breaking technology using torsional impactor.From the theoretical analysis,the influence of the torque impact on the stick-slip vibration is studied.Then rock constitutive UMAT file is written and the rock-breaking process of the PDC bit under the torsional impact is simulated.The factors considered in the research are increasing gradually and the study of the problem is from shallow to deep.The research method also has certain originality,and the theory and simulation complement each other.A series of conclusions,such as the impact of torsional impact on rock-breaking process of PDC bit,have certain reference value for future related research.