Abstract:

Shale hydration and dispersion lead to instability of the borehole wall, which has always been a problem in oil and gas drilling engineering. Physically plugging pores and micro?cracks in shale through nano plugging agents is the best way to improve the stability of shale formations. In this work, the silane coupling agent KH560 was used to modify the high?concentration silica sol. The principle of soap?free emulsion polymerization was used in combination with solvothermal synthesis to graft acrylic acid (AA) and styrene (St) monomers on the surface of modified SiO₂ particles. Thus, a new type of elastic pressure?bearing plugging agent with polymer?encapsulated nanoparticles was successfully developed. Taking medium pressure filter loss as the evaluation index, the best synthesis conditions were obtained: The reaction temperature was 60 ℃, the reaction time was 3.0 h, the monomer ratio was 3∶2, the pre?emulsification time was 10.0 min, the total monomer mass was 6.67%, and the amount of initiator was 0.40%. In addition, Zeta potential, particle size analyzer and transmission electron microscope proved that the median particle size of the prepared STA?1 plugging agent was 45.3 nm. Finally, a core displacement experiment was used to simulate the shale layer to investigate the actual plugging effect of STA?1. The results revealed that 1.00% STA?1 showed good water plugging ability for sand filled pipes with permeability below 2 000 mD, and the plugging rate was higher than 85%.

Key words: Silica sol, Acrylic acid, Styrene, Nano?plugging agent

摘要：

页岩水化和分散导致井壁失稳一直是油气钻井工程中的难题，通过纳米封堵剂物理封堵页岩中的孔隙和微裂缝，是提高页岩地层稳定性最好的方法。采用硅烷偶联剂KH560对高浓度的硅溶胶进行改性处理，运用无皂乳液聚合原理，在改性SiO₂粒子表面接枝丙烯酸（AA）和苯乙烯（St）单体，成功研制出一种聚合物包裹纳米颗粒的新型弹性承压封堵剂。通过Zeta电位及粒度分析仪和透射电子显微镜证明所制备的STA?1封堵剂粒径中值为45.3 nm。以中压滤失量为评价指标得到最佳合成条件：反应温度为60 ℃，反应时间为3.0 h，m（St）/m（AA）=3∶2，分散搅拌时间为10.0 min，单体质量分数为6.67%，引发剂质量分数为0.40%。最后，利用岩心驱替实验模拟页岩考察STA?1的实际封堵效果。结果表明，质量分数为1.00%的STA?1对渗透率小于2 000 mD的填砂管表现出良好的堵水能力，封堵率大于85%。

关键词: 硅溶胶, 丙烯酸, 苯乙烯, 纳米封堵剂