The Statistical Research Of The Failure Rules Of Drill String Based On Drilling Fluid Lubrication

The drill string is an essential downhole tool in the process of oil drilling,and the failure of drill string seriously restricts the drilling speed and the well construction period.As the working condition of drill string is very poor and the stress state is very complex,the drill string failure,such as corrosion,wear,washout,fracture,is more likely to happen,especially in gas drilling.According to the statistical data of the oil field,the failure frequency of the gas drilling tool is 2 to 10 times than the mud drilling and the working life is only 1/5 to 1/3 of the mud drilling,because of the lack of the lubrication of the drilling fluid in the gas drilling.Therefore,it is of great significance to study the lubrication of drilling fluid to reduce the failure of drilling tools.In this paper,on the basis of previous studies,based on the failure mechanism of drill string under the lubrication of drilling fluid,we have conducted some statistical researches on the failure rules of the of drill string in different drilling fluid,And through the comparison of the field data and experimental data,this paper puts forward some preventive measures for the failure of drilling tools in order to provide reference in practice.Firstly,the failure mechanism of drill string is analyzed in detail by using the fault tree analysis method,it is concluded that the failure mode and failure characteristics of gas drilling tools are different from those of mud drilling.Secondly,the statistics of drilling tool failure in the oil field and the experimental data are analyzed in this paper,it is concluded that the lubrication of drilling fluid can effectively reduce drilling tool failure probability,and the lubrication effect of drilling fluid is analyzed from five aspects of drilling fluid itself,corrosion,erosion,vortex and vibration.At last,this paper suggests that the viscosity and density of drilling fluid should be increased appropriately in the well section with frequent failure,so as to increase the lubricating effect of the drilling fluid and reduce the economic loss caused by the failure of the drilling tool as far as possible.