纳米二氧化硅对盐水钻井液性能的影响

在油气井钻进过程中,井壁发生缩径和掉块往往是由于泥页岩吸水膨胀导致的。针对这种情况,提出使用纳米二氧化硅封堵泥页岩的纳米级孔喉,从而降低其渗透率、减缓水分侵入的思路。通过测试钻井液的黏度、滤失量和膨胀量,评价了纳米二氧化硅对盐水钻井液性能的影响。室内实验结果表明,纳米二氧化硅改善钻井液性能,必须是在其抗盐的基础上才能实现,即需使用抗盐土配浆;浓度为1%~5%的纳米二氧化硅通过增加颗粒间的内摩擦力,既而提高了钻井液的黏度,然而纳米二氧化硅材料对于盐浓度比较敏感;纳米二氧化硅颗粒可以沉积在滤饼表面封堵滤纸孔隙,降滤失效果明显,滤失量降低率可达40.2%;其通过封堵黏土的孔隙,起到了抑制黏土吸水膨胀的作用。优选出的二氧化硅最优加量为3%,其抗盐可至12%;综合考虑滤失、膨胀量实验结果和性价比,选定3%NP+4%Na Cl+SWM-B为最优配方。

Effect of Nano SiO2 on Performance of Saltwater Drilling Fluid

Nano SiO2 (silicon dioxide) is proposed to plug the nano sized pore throats in shale formation to retard invasion of filtrate into the formation in contact with drilling fluid, thus avoiding tight hole and borehole collapse. Effect of nano SiO2 on the improvement of drilling fluid properties was evaluated by measuring the viscosity, filter loss of drilling fluid and shale swelling. The results showed that to improve the performance of the drilling fluid, the nano SiO2 used should be resistant to salt contamination. Treatment of the drilling fluid with 1%-5% nano SiO2 increased the viscosity of the fluid by increasing inter-particle friction. On the other hand, the nano SiO2 was sensitive to the concentration of salt. Laboratory experiments at room temperature showed that by adding 3% nano SiO2 into the drilling fluid, it will have the capacity of tolerating salt commination to 12%. Particles of the nano SiO2 can deposite into the filter cake, reducing the filter loss of the drilling fluid (percent reduction of filter loss volume as high as 40.2%). By retarding the invasion of filtrate, nano SiO2 improved the inhibitive capacity of the saltwater drilling fluid. Nano SiO2 remarkably reduced the volume of filter loss of saltwater drilling fluid (salt concentration less than 8%).