延长组长7段页岩水基钻井液封堵剂评价研究

Evaluation Study of Shale Water-based Drilling Fluid Plugging Agent in Chang 7 Member of Yanchang Formation

针对超低孔超低渗页岩地层的井壁失稳问题,以延长组长7段页岩为参考对象,采用X射线衍射、渗透率、孔隙度、比表面积、平均孔径测定和扫描电子显微镜等手段,分析了矿物组分、岩性特征,提出了页岩井壁维稳思路。借助模拟“标准厚泥饼”封堵评价方法,对ZD–1、JB53、EP–2和ZD–3等封堵剂最佳加量及其复配的封堵效果进行评价,优选得到了高效封堵的复配封堵剂SPA–1。在延长页岩用水基甲酸钾钻井液体系中加入4.0%SPA–1后,其流变性易于控制且渗透率降低率高达94.20%,作用前后的模拟岩芯电镜图像进一步验证了其封堵效果,并分析了封堵剂封堵作用机理。结果表明,SPA–1集合理的粒度级配和刚柔性粒子协同作用可以实现有效封堵,有利于延长组长7段页岩井壁稳定。

In view of the problem of well wall instability in ultra-low porosity and ultra-low permeability shale formations,taking the shale of Chang 7 Member of Yanchang Formation as the reference object,the mineral composition and lithology characteristics are analyzed by means of X-ray diffraction,permeability,porosity,specific surface area,average pore diameter measurement and scanning electron microscopy,and the idea of maintaining wellbore stability of shale is put forward.By using the simulated“standard thick mud cake”plugging evaluation method,the optimal dosage of ZD–1,JB53,EP–2 and ZD–3 plugging agents and the plugging effect of their combination were evaluated,and the effective compound plugging agent SPA–1 was selected.After adding 4.0%SPA–1 to the water-base potassium formate drilling fluid system for Yanchang shale,the rheology is easy to control and the permeability reduction rate reaches 94.20%.The simulated core electron microscopy images before and after the application further verified the plugging effect and analyzed the plugging mechanism of the plugging agent.The results show that SPA–1 set reasonable particle size distribution and the synergistic effect of rigid and flexible particles can achieve effective plugging,which is conducive to the stability of shale wall of Chang 7 Member of Yanchang Formation.