Analysis of mechanical strengths of extreme line casing joint considering geometric, material, and contact nonlinearities

To address the challenges associated with difficult casing running,limited annular space,and poor cementing quality in the completion of ultra-deep wells,the extreme line casing offers an effective solution over conventional casings.However,due to its smaller size,the joint strength of extreme line casing is reduced,which may cause failure when running in the hole.To address this issue,this study focuses on the CST-ZTΦ139.7 mm×7.72 mm extreme line casing and employs the elastic-plastic mechanics to establish a comprehensive analysis of the casing joint,taking into account the influence of geometric and material nonlinearities.A finite element model is developed to analyze the forces and deformations of the extreme line casing joint under axial tension and external collapse load.The model investigates the stress distribution of each thread tooth subjected to various tensile forces and external pressures.Additionally,the tensile strength and crushing strength of the extreme line casing joint are determined through both analytical and experimental approaches.The findings reveal that,under axial tensile load,the bearing surface of each thread tooth experiences uneven stress,with relatively high equivalent stress at the root of each thread tooth.The end thread teeth are valuable spots for failure.It is observed that the critical fracture axial load of thread decreases linearly with the increase of thread tooth sequence.Under external pressure,the circumferential stress is highest at the small end of the external thread,leading to yield deformation.The tensile strength of the joint obtained from the finite element model exhibits a relative error of less than 7%compared to the analytical and experimental values,proving the reliability of the finite element model.The tensile strength of the joint is 3091.9 k N.Moreover,in terms of anti-collapse capability,the joints demonstrate higher resistance to collapse compared to the casing body,which is consistent with the test results where the pipe body experiences collapse and failure while the joints remain intact during the experiment.The failure load of the casing body under external collapse pressure is 87.4 MPa.The present study provides a basic understanding of the mechanical strengths of extreme line casing joint.

无创正压通气治疗对急性呼吸衰竭患者拔管后再插管和病死情况的影响

目的明确无创正压通气(NPPV)治疗方式对急性呼吸衰竭(RF)患者拔管后再插管率和病死率的影响。方法联合检索美国国家生物技术信息中心(NCBI PubMed)、中国知网(CNKI)及万方数据库,查询2000年以来有关NPPV对RF患者拔管后进行呼吸支持和治疗的随机对照试验研究,采用Stata 12.0统计软件对数据进行分析,以合并Ol^R值及95%CI评价对拔管后NPPV辅助治疗患者的再插管率和病死率。结果依据纳入和排除标准,共9篇临床随机对照研究,研究对象996例。其中,NPPV治疗组518例,常规治疗组478例。NPPV治疗组和常规治疗组再插管率为40/518(7.7%) vs 110/478(23.0%)(P<0.05);病死率为35/518(6.8%) vs 83/478(17.4%)(P <0.05)。与常规治疗组比较,拔管后NPPV治疗可降低患者再插管和病死的发生风险,相应[Ol^R=0.260和0.340,(95%CI:0.180,0.390)和(95%CI:0.220,0.510)]。结论 RF患者拔管后NPPV治疗有助于降低患者再插管和病死的发生风险。