页岩地层核壳结构纳米封堵剂研制及应用

页岩地层纳米级微孔、微裂缝极其发育,常规封堵剂粒径较大,难以对页岩形成有效的致密封堵。首先采用硅烷偶联剂KH570对纳米SiO_2进行超声表面改性,进而通过乳液聚合法,以苯乙烯、甲基丙烯酸甲酯为单体,过硫酸钾为引发剂与表面改性纳米SiO_2进行接枝共聚,制备了一种具有核壳结构的纳米封堵剂。借助红外光谱、透射电镜、热重实验对产物进行了表征,通过页岩压力传递实验测试了其致密封堵性能,探讨了其作用机理。结果表明:该纳米封堵剂能够有效封堵页岩纳米级孔缝结构,阻缓压力传递与滤液侵入,显著降低页岩渗透率,提高裂缝性页岩井壁稳定性。以该纳米封堵剂为核心处理剂构件了一套高性能页岩水平井水基钻井液体系,具有较好的致密封堵、抑制、润滑等关键性能。该体系在威远区块X井三开长裸眼井段应用过程中,井眼始终保持稳定,摩阻低,定向段无拖压显示。

Development and Application of Nano Plugging Agent with Core-Shell Structure for Shale

Nano-scale pores and fractures are well developed in shale. Because of the large particle size, conventional plugging agent is difficult to form effective plugging for shale. First, nano SiO2 particles were modified by silane coupling agent KH570 under ultrasound conditions. Furthermore, nano plugging agent with core-shell structure was synthesized through the radical graft copolymerization on the surface of the modified nano SiO2 particles by emulsion polymerization method. In the reaction, we choose styrene and methyl methacrylate as monomers and potassium persulfate as initiator. Nano plugging agent was characterized by infrared spectroscopy, transmission electron microscopy and thermogravimetry experiments. The plugging performance of nano plugging agent was studied by the pressure transmission tests on shale and the mechanism was discussed. The results showed that this nano plugging agent can effectively plug nano-scale pores and fractures of shale, reduce pressure transmission, filtrate invasion and shale permeability, thus enhancing wellbore stability of fissured shale. A high performance water-based drilling fluid system with good key performaces such as polugging, inhibition, lubrication an so on for shale horizontal wells was developed with the nano-plugging agent as the key component. During the application of this system in the third section of X Well in weiyuan block, the wellbore remains stable, the friction is low, and there is no drag pressure display in the directional section.