There are abundant oil and gas resources in the deep parts of the earth.As more and more deep and ultra-deep wells are drilled,the number of drilling tool failure accidents(breaking and leakage)increases gradually year after year.In order to further clarify the reasons for drilling tool failure in large-sized wellbores of deep and ultra-deep wells and reduce the accidents of drilling tool failure,this paper reviews the behaviors and characteristics of recent drilling tool failure in PetroChina's three major oilfields in the western China,and analyzes the reasons for 5 consecutive accidents of drilling tool breaking in 17-1/2"wellbore of a typical ultra-deep well in one oilfield of western China.Firstly,the drilling tool dynamics model is established based on the Hamilton principle and the Newmark-β method.Then combined with the rain-flow method and the Miner fatigue damage accumulation theory,the movement,stress and fatigue life of drilling tool are quantitatively evaluated,and the accuracy of the model is verified.Finally,the drilling technological measures for preventing drilling tool breaking in large-sized wellbores are proposed.And the following research results are obtained.First,drilling tools failure mainly occur in upper large-sized wellbores of deep and ultra-deep wells,with the failure positions concentrating at the joint of lower tool or the weak part of small-sized tool.Second,high-frequency bending stress induced by lateral vibration of drilling tool is the main factor leading to fatigue failure of drilling tools,and continuous severe lateral vibration can lead to fatigue failure of drilling tools within hours.Third,increasing BHA stiffness and drilling with"high WOB+low RPM"can help to reduce lateral vibration severity of drilling tools.Fourth,the severe lateral vibration caused by small BHA stiffness and inappropriate drilling parameters,combined with the repeated alternation of"neutral point"at tool joints and weak parts of small-sized tools,is the direct cause of the consecutive drilling tool breaking in the typical case well.In conclusion,the proposed model can be used to quantitatively evaluate the fatigue failure of drilling tools,and the prevention measures can provide technical reference for preventing drilling tool failure in large-sized wellbores of deep and ultra-deep wells.
关键词
深井超深井/大尺寸井眼/钻柱动力学/横向振动/高频弯曲应力/疲劳失效/防控措施
Key words
Deep and ultra-deep wells/Large-sized wellbores/Drill string dynamics/Lateral vibration/High-frequency bending stress/Fatigue failure/Prevention and control measures
维普
万方数据