Taking into account formation heterogeneity and anisotropy around a fault, and based on the weak surface strength criterion, the influence of the formation anisotropy on in-situ stresses was analyzed, and the changing pattern of the borehole collapse pressure with the fault strike and dipping angle was discussed.Furthermore a model for calculating the collapsing pressure through faults was established and the collapsing pressure analyzed.The results show that maximum and minimum horizontal stresses increase with the increasing values of Eh/Ev and vv/vh, so the influence of formation anisotropy on in-situ stresses should be considered when the hole section cuts through a fault.Collapse pressures corresponding to different fault types, fault strikes or dip angles are different, and there is no inclination azimuth where collapse probability is monotonically increasing or decreasing;safe area and dangerous area occur alternately.Fault types and the weak surface structure should be considered in well trajectory designs, with the fault being drilled through at the reasonable angle.The prediction model developed here was applied to Well A in Bohai oilfield, achieving sound engineering effects, with the hole enlargement being generally less than 10%.The results of this paper have a guiding significance for drilling safety through faults, which can provide theoretical reference for designing wellbore trajectories.%考虑断层周围地层非均质性和各向异性,根据弱面强度准则,分析了地层各向异性对地应力的影响,探讨了井壁坍塌压力随断层走向及倾角的变化规律,建立了过断层的坍塌压力计算模型,开展了不同性质断层构造坍塌压力分析,结果表明:随着Eh/Ev、vv/vh值的增大,水平最大应力、水平最小应力增加,过断层应考虑地层各向异性对地应力的影响;不同的断层类型、断层走向及倾角所对应的坍塌压力存在差异性,且不存在单调递增或递减的井斜方位,安全区域和危险区域交替出现;井眼轨迹设计应考虑断层类型及弱面结构,选择合理的钻入角钻穿断层.将本文预测模型用于渤海油田A井取得了良好工程效果,井眼扩大率基本小于10%.本文研究结果对过断层时钻井安全具有指导意义,可为井眼轨迹设计提供理论参考.
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