Research On Mechanical Characteristics Of Air Drilling Drilling String

Based on the analysis of the macroscopic mechanical properties of the drill string in air drilling,the vibration characteristics and dynamic response characteristics of the drill string in air drilling are discussed by numerical simulation.The following work is carried out and the following understanding is made.The main failure formof the drilling tool,in the air drilling,is the fracture failure;nearly half of the failure is the drilling collar thread fracture.Compared with the mud drilling,the air drilling failure is even worse than that of the mud drilling.A static analysis model of the bottom hole assembles(BHA)was established,and the BHA was statistically analyzed.The effects of drilling pressure,drilling fluid density,well angle,formation anisotropy and bore diameter on drilling rigging ability are analyzed,which provide a theoretical basis for air drilling trajectory control.A dynamic analysis model of BHA was established,and the kinetic characteristics of BHA were analyzed by harmonic response analysis and modal analysis.Because there is no viscous damping effect of the drilling fluid in the air drilling,the vibration frequency of the drill string in the air drilling is higher than that in the mud drilling.The drilling fluid has a stronger damping effect on the lateral and torsional vibrations of the drill string and has different effects on the frequency of the different orders and has a great effect on the low frequency.Under normal circumstances,the low order frequency plays a dominant role in the drill string vibration,So the vibration of the drill string in air drilling is much more seriously than drilling fluid drilling.The vibration frequency of the drill string decreases with the increase of the depth of the well,which leads to the relative concentration of the critical speed of each step,which indicates that the change of the rotational speed in the drilling area is easy to cause resonance.Therefore,in the deep well drilling,the engineers should pay special attention to the selection of drilling parameters,while the use of shock absorber device to avoid the phenomenon of drill string resonance.