海洋钻井套管安全下放速度计算模型研究

Safe running velocity model of offshore casing pipes

由于海上探井泥线以上的井筒结构为长细杆结构,下套管时过大的冲击载荷常常会造成井口损坏或井筒失稳,确定套管极限下放速度是安全作业控制的关键。本文从探井井身结构的特征入手,开展了井口与井筒管柱的整体受力分析。基于压杆稳定性理论,建立了探井作业条件下井口和井筒承载力计算模型。利用能量守恒定理,建立了坐挂套管条件下冲击载荷的计算模型。以隔水导管承载力、井口结构强度、井筒失稳和薄弱地层破裂压力为约束条件,建立了套管最大下放速度计算模型。以渤海海上典型探井为例,结合地层土质参数与钻井作业工况,利用该模型分析了套管下放速度对井口载荷及井筒稳定性的影响。经海上探井的现场应用与实践证明,所建立的理论模型对海上钻井设计和现场施工具有很好的指导意义。

The wellbore of an offshore exploratory well above the mudline can be considered as a long slender member bar. High casing running may lead to wellhead damage and instability. It is crucial to calculate the casing pipe's running velocity. Based on the wellbore configuration, this paper conducted mechanical analysis of the wellhead and wellbore string. According to compressed bar stability theory, wellhead and wellbore bearing capacity calculation models were established. Based on the energy conservation principle, impulsive load calculation models were set up. Setting conductor-bearing stability, wellhead strength, wellbore instability and weak formation's fracture pressure as constraint conditions, the maximum casing pipe running velocity models were derived. Taking a Bohai Basin exploration well as a computational example, this paper analyzed the influence of casing running velocity on wellhead loading and wellbore stability. After being applied in exploration wells, this theoretical model was proved to be significant for offshore drilling design and site operation.