海南FS复杂断块油田钻井防塌误区及井壁稳定对策

Misunderstanding of the Wellbore Collapses for Complex Fault-Block of FS Oilfield, Hainan and Its Technical Countermeasures for Wellbore Collapse

断层对其周边地应力大小和方向均有较大影响,且断层破碎带作为一种岩石弱面,其力学强度较连续完整地层明显偏低,断层是钻遇/钻邻断层井井壁稳定的主控因素,对于复杂断块油田更是如此。然而长期以来,业界对于该机理认识不清,往往简单地基于连续完整地层的坍塌压力,来进行钻井液密度及防塌性能设计,井壁稳定设计未充分考虑断层因素,导致坍塌压力数值失真、相应地防塌设计效果达不到预期,钻井防塌陷入误区。本研究以FS断块油田为例,深刻分析近断层区域井壁坍塌机理,揭开当前近断层或过断层井防塌工作误区,提出两套复杂断块油田井壁稳定研究技术路线,并开展了实例研究,可为类似复杂断块钻井防塌提供参考借鉴。

The fault is the key factor for wellbore instability of the area nearby because of two reason, especially for the complex fault-block reservoir. One reason is that the fault impacts the in-situ stress of the area nearby, and another is the strength of the faulted zone is lower than the area far from the fault. However, the collapse mechanism of the area nearby fault has not been known by the drilling engineers and the related personnel, and the collapse pressure of the continuous formation is often used for the wellbore stability of the area far from the faults, which lead to the deviation from the down hole condition and poor wellbore instability results. The misunderstanding for the wellbore instability named FS complex fault-block has been analyzed in this paper, and two technical methods for wellbore collapse research nearby faults have been developed. The case study with one method shows that the influence of fault on the collapse pressure and the mud window nearby. The results of this paper shall be helpful for improving the wellbore collapse prevention nearby the faults, especially for the complex fault-block reservoir.