Study On The Optimum Design Of The Direct Push Sampling Drilling Tool

The problem of soil stratum pollution is prominent in China.Sampling is the key point of stratum pollution investigation.At present,two kinds of technologies are mainly adopted for sampling polluted formation:direct push(percussive)drilling and vibration(high frequency audio)drilling.In the process of direct push drilling and percussion drilling,the main failure mode between sampling bit and formation is shear,which is quite different from the traditional rotary drilling method.The coupling between the two is closely related to formation,bit structure,material and drilling parameters.In this paper,the research is carried out in order to lay a foundation for the optimization of sampling drilling tool and technology.In this paper,the equivalent mathematical model of drill string formation interaction is established,and the law of formation vibration response under excitation load and drillstring resonance is studied.Then,based on the ANSYS finite element analysis software,the coupling model between bit and formation is established,and the simulation analysis is carried out.The influence of bit structure parameters and drilling parameters on formation damage effect is studied.Finally,optimize the bit structure,establish the coupling model between drill string,bit and formation,simulate and analyze the influence of drill string and sampling drilling tool on formation drilling under high frequency excitation load.Some research results are as follows:(1)The theoretical analysis results show that the displacement of rock stratum vibration response is in direct proportion to the maximum amplitude of excitation load,in inverse proportion to its own natural frequency and relative damping ratio,and the occurrence of stratum vibration response has phase difference compared with the impact load.With the increase of formation stiffness,the peak value of vibration response force increases,and the change frequency of response force accelerates;with the increase of drilling depth,the response force produced by the drill string resonance decreases.(2)The simulation results show that:? under the static pressure condition,the change of bit outer diameter structure has a great influence on the drilling efficiency.When the outer diameter is reduced by 1mm,the drilling soil layer can maintain good cutting and sample fidelity.Compared with the original structure bit,the maximum equivalent stress of soft rock is increased by 77.7%,and the equivalent stress of hard rock is reduced by 43.1%.? Under the impact condition,the stress level of the rock stratum is relatively low.Reducing the outer radius structure in the range of 0.5-1.0mm can effectively improve the rock breaking drilling ability and keep the drilling tool at a low stress level.? Under vibration condition,when the outer radius of the bit is reduced within 0.5-1.Omm,the average response force and axial displacement of the rock stratum are improved,which can maintain the lower stress level of the drilling tool and effectively improve the drilling efficiency.? Under the condition of 1.0mm reduction of outer radius,the simulation of drilling tool formation shows that the response force of formation vibration increases with the increase of hardness,and the drilling efficiency is effectively improved under the high frequency excitation load,but the material strength of drilling tool still needs to be improved to prevent its damage.In this paper,through theoretical and simulation analysis,the optimization design of the direct push sampling drilling tool is studied,which provides a reference for the subsequent sampling drilling tool structure design and sampling process optimization.It has a certain reference significance for improving the drilling limit depth,sampling efficiency and the service life of drilling tools.