Static & dynamic characteristics of drill string during gas drilling

Focusing on the engineering problem of the violent vibration and the frequent failure of the drill tools in gas drilling,the static and 3-directional coupling vibratory models of the whole drill string system are built,and the method for computing the damping of cyclic medium is studied.Taking it as example that the gas drilling section of a field well in east Sichuan province,the comparison is conducted between the results of mud vibration model and the field data and laws measured by ESSO Production co,America,which validates the feasibility of the model;the static characteristics and dynamic properties of the whole drill string in gas are studied quantitatively,and compared with ones when they work in mud.It is shown that each drill tool's axial load and axial stress in gas are far above the ones in mud,and the amplitude-frequency of the longitudinal,transverse,torsional vibration and whirl are more severe,the drill string in gas needs to bear more complex alternating stress in drilling,which is one of the factors to result in frequent failure of drill tools.The static characteristics and dynamic properties of drill string in gas drilling are clarified and the mechanism of the drill tools' failure is revealed and effective precaution is studied.