钻杆振动致旋转防喷器胶芯松动的作用机理及解决对策OA

During underbalanced drilling,the intense vibration of rubber cores in rotary blowout preventers can induce frequent loosening and even detachment of anchor bolts,threatening the safety of drilling operations.To explore its failure mechanisms and put forward effective solutions,this paper establishes a three-dimensional finite element model and a flexural-torsional dynamic model for rubber core-drill pipe system by combining finite element numerical simulation and experimental verification.The two models are employed to systematically analyze the variation patterns of stress field distribution,displacement response,vibration frequency and amplitude under two typical working conditions of drill pipe,i.e.,tripping in and rotating.A focus is put on the comparison analysis of the influence of 18° and 45° tool joints on the mechanical behaviors of the system,and the dynamic cause of bolt loosening is identified.Accordingly,a bolt anti-loosening scheme is proposed and validated on site.The following results are obtained.First,the 45° tool joint can induce high-frequency vibrations at the transition taper of rubber core,whose frequency is as high as 16.7 Hz,3.6 times that of the 18° joint.And the peak stress is up to 70 MPa,which is much higher than that of 18° joint(41 MPa).Second,under rotating conditions,the vibration frequency of rubber core increases with the increasing rotation speed,and the amplitude declines overall with the increasing rotation speed.The high-frequency alternating load induced by high-slope joint is the root cause of preload loss and nut loosening.Third,the proposed flat washer-spring washer-split pin combined mechanical anti-loosening scheme is validated to be reliable via the Junker vibration test.The field application indicates that this scheme can match well with different slopes of joints to inhibit loosening effectively,while the wear of the rubber core is normal.In conclusion,the modeling simulation and experiments reveal the loosening mechanisms of rubber core bolt under high-frequency vibration.The research results significantly improve the operating reliability and safety of rotary blowout preventers under complex working conditions.