裂缝性泥页岩地层防塌误区及强封堵防塌对策

对于裂缝发育等破碎性地层，在井筒内外压差作用下钻井液极易沿裂缝等天然通道侵入地层，致使近井裂缝发育带孔隙压力增加，引发泥页岩水化膨胀及强度性能下降，导致坍塌压力增加，从而使得井壁垮塌越加严重，搞清破碎性地层垮塌机理至关重要。结合延安气田石盒子和石千峰组裂缝性泥页岩“越提密度、垮塌越严重”井塌处理误区，指出缺乏对裂缝有效封堵是症结所在。为此提出适用于裂缝发育等破碎性地层“封堵为先、抑制水化、合理密度”的防塌技术对策，在此基础上，优选出延安气田强封堵钻井液配方并在现场成功应用，相关技术思路及研究成果可为类似破碎性地层防塌提供参考。 

Misunderstanding of Fractured Shale Collapse Prevention and Plugging Method for Preventing Borehole Collapse

In fractured formations, drilling fluids under the action of pressures inside and outside of the borehole wall are very easy to invade the formation along the fracture channels, thereby increasing the pore pressure in the near-wellbore where fractures are quite developed, causing shale to hydrate and swell and strength decrease, increasing the collapse pressure of the formations, and hence exacerbating borehole wall collapse. In dealing with borehole wall collapse occurred in drilling the Shihezi formation and the Shiqianfeng formation in Yan'an gas field, it was found that the borehole wall collapse became more severe when mud weight was being increased. Study on this situation found that the failure of the borehole wall collapse just came from the lack of effective plugging of the fractures in the two formations. Understanding this, a countermeasure of preventing the collapse of fractured formations was developed, which can be described as "plugging the fracture has the top priority, inhibiting the hydration of the formations and using reasonable mud weight". Based on this measure, an optimized drilling fluid with high plugging capacity was developed for use in drilling operation in the Yan'an gas field. The technical clues in this study can be used as a reference for preventing borehole wall collapse in drilling the similar fractured formations.