An analytical formulation is developed to investigate the stability of a deep, inclined borehole drilled in a geologic medium and subjected to an internal pressure and a non_hydrostatic stress field. The formulation c...An analytical formulation is developed to investigate the stability of a deep, inclined borehole drilled in a geologic medium and subjected to an internal pressure and a non_hydrostatic stress field. The formulation consists of a three_dimensional (3_D) analysis of stresses around a borehole, combined with internal pressurization of the borehole to obtain an approximate solution of the overall stress distribution. The orientation of the borehole, the in_situ stresses and bedding plane can all be arbitrarily related to each other to represent the actual field situations. Both tensile failure and shear failure potentials of a borehole are investigated. The failure criteria applied assume that when the least principal stress exceeds the strength of the formation in tension, a tensile failure occurs. Shear failure is represented using the modified Drucker_Prager failure criterion for anisotropic materials. A parametric study is carried out to assess the effect of material anisotropy, bedding plane inclination and in_situ stress conditions on borehole stability. Results of the parametric study indicate that wellbore stability is significantly influenced by a high borehole inclination, high degree of material anisotropy, in_situ stress conditions and high formation bedding plane inclination. The stability of a borehole in an elasto_plastic medium is also investigated. In order to evaluate the extent of the plastic zone around a borehole and the effect of anisotropy of the material on this plastic zone, a mathematical formulation is developed using theories of elasticity and plasticity. The borehole is assumed to be vertical, subjected to hydrostatic stresses, and drilled in a transversely isotropic geologic medium. A parametric study is carried out to investigate the effect of material anisotropy on the plastic behavior of the geologic medium. Results indicate that the stress distribution around a borehole, the extent of the plastic zone, and the failure pressure are influenced by the degree of material anisotropy and展开更多
某井在钻井作业时产生卡钻,在解卡操作过程中发生了127 mm×9.19 mm G105钻杆的断裂失效事故。通过对失效钻杆断口的宏观形貌分析、钻杆材质的一系列理化性能检测,以及钻井作业操作过程的综合分析,得出了钻杆失效的原因为解卡过程...某井在钻井作业时产生卡钻,在解卡操作过程中发生了127 mm×9.19 mm G105钻杆的断裂失效事故。通过对失效钻杆断口的宏观形貌分析、钻杆材质的一系列理化性能检测,以及钻井作业操作过程的综合分析,得出了钻杆失效的原因为解卡过程中钻杆接头与井壁岩石或沉砂发生摩擦磨损,产生的摩擦热达到了钻杆接头材料的相变温度,钻杆在井下发生了“二次热处理”,从而降低了材料的强度和性能。同时,摩擦磨损导致了钻杆有效截面的不断减少,当有效截面处的拉伸应力超过材料屈服强度时,钻杆发生塑性断裂失效。提高井壁的稳定性、增加短程起下钻频次、保持泥浆循环通道畅通,是解决此类钻具失效的有效手段。展开更多
文摘An analytical formulation is developed to investigate the stability of a deep, inclined borehole drilled in a geologic medium and subjected to an internal pressure and a non_hydrostatic stress field. The formulation consists of a three_dimensional (3_D) analysis of stresses around a borehole, combined with internal pressurization of the borehole to obtain an approximate solution of the overall stress distribution. The orientation of the borehole, the in_situ stresses and bedding plane can all be arbitrarily related to each other to represent the actual field situations. Both tensile failure and shear failure potentials of a borehole are investigated. The failure criteria applied assume that when the least principal stress exceeds the strength of the formation in tension, a tensile failure occurs. Shear failure is represented using the modified Drucker_Prager failure criterion for anisotropic materials. A parametric study is carried out to assess the effect of material anisotropy, bedding plane inclination and in_situ stress conditions on borehole stability. Results of the parametric study indicate that wellbore stability is significantly influenced by a high borehole inclination, high degree of material anisotropy, in_situ stress conditions and high formation bedding plane inclination. The stability of a borehole in an elasto_plastic medium is also investigated. In order to evaluate the extent of the plastic zone around a borehole and the effect of anisotropy of the material on this plastic zone, a mathematical formulation is developed using theories of elasticity and plasticity. The borehole is assumed to be vertical, subjected to hydrostatic stresses, and drilled in a transversely isotropic geologic medium. A parametric study is carried out to investigate the effect of material anisotropy on the plastic behavior of the geologic medium. Results indicate that the stress distribution around a borehole, the extent of the plastic zone, and the failure pressure are influenced by the degree of material anisotropy and
文摘某井在钻井作业时产生卡钻,在解卡操作过程中发生了127 mm×9.19 mm G105钻杆的断裂失效事故。通过对失效钻杆断口的宏观形貌分析、钻杆材质的一系列理化性能检测,以及钻井作业操作过程的综合分析,得出了钻杆失效的原因为解卡过程中钻杆接头与井壁岩石或沉砂发生摩擦磨损,产生的摩擦热达到了钻杆接头材料的相变温度,钻杆在井下发生了“二次热处理”,从而降低了材料的强度和性能。同时,摩擦磨损导致了钻杆有效截面的不断减少,当有效截面处的拉伸应力超过材料屈服强度时,钻杆发生塑性断裂失效。提高井壁的稳定性、增加短程起下钻频次、保持泥浆循环通道畅通,是解决此类钻具失效的有效手段。
