Research On The Breaking Mechanism Of Anisotropic Shale Based On Drill String Vibration Characteristics

China is rich in shale gas resources,which has laid a strong foundation for the development of shale gas industry.Drilling shale gas quickly and efficiently is the key.Sichuan province is the first in China to carry out a study and exploration on shale gas.The geological conditions of shale gas in Sichuan province is complex with large strata dip,and shale reservoir is strongly anisotropic.Shale gas reservoirs are generally buried deep,distributed in 3000 meters underground.The shale is more compact making the reservoir drilling worst.When drilling in shale reservoirs with high strength and high formation dip,comprehensive drilling cost is higher,and the average drilling cost of a well is about 75 million RMB,which greatly restricts the development of the shale gas industry in our province.PDC bit has been achieved in the drilling of sandstone and shale reservoirs with strong heterogeneity,high abrasive.However,the research focus of PDC breaking rock mechanism mainly concentrated in the isotropic sandstone rock.This paper is based on the international cooperation project of Science and Technology Department in Sichuan province,which is named "The study on crushing mechanism of anisotropic shale based on the dynamic characteristics of drilling string system".Aiming at the complicated joint angle of shale reservoir and the changes of the joint angle on the drilling pressure,torque and other key drilling parameters,a simulation experiments indoor of micro PDC bit broking shale is conducted.On this basis,this paper establishs a finite numerical element model of micro PDC bit broking shale.By comparing the results of the indoor simulation experiment and simulation analysis,this paper further studies the influence mechanism of the joint dip on crushing shale.The main contents of this dissertation include the following aspects:(1)making the Longmaxi shale with different angle as the research object,tensile strength tests and three axis compression tests are carried out.The influence of the different angle on the rock elastic plastic parameters is analied,while the constitutive model of shale and the key elasticity parameters is determined.(2)carring out the research of drilling string mechanics,studying the basic characteristics of main mechanical parameters such as axial force,drill string torque,bending moment,analyzing the static mechanical model of drill string.By using the similarity criterion,the relationship between the drilling parameters in the actual production and the experimental conditions is determined.(3)carring out the indoor experiments of micro PDC bit broking shale based on the drill string vibration characteristics,which includes the design of experimental device,drilling experiment of micro PDC bit-shale,drilling experiment of drill string-micro PDC bit-shale,he changing characteristics of weight on bit,torque,cuttings crushing weight with the shale joint angle under different conditions are analyzed in-depth.Based on the dynamic characteristics of drill string,the variation characteristics of the waves of weight on bit,torque and the displacement of the bit are analyzed.(4)developing a finite element numerical model of micro PDC bit-bedding shale,and the basic characteristics of weight on bit,torque and ther parameters in different angles are analyzed.On this bass,use two node linear space beam element to simulate the drill string,which is coupled to the numerical model.The influence of the stress characteristics at the upper end of the drill string and the movement characteristics of the bit body are researched.