粘土矿物及钻井液电动电位变化规律研究

Research on the changing tendency of zeta potential of the clay minerals and drilling fluid

分析了导致粘土矿物膨胀分散的原因,研究了粘土矿物的电动电位(ζ电位)变化规律;提出了粘土矿物及钻井液电性的转变方法。即有机正电处理剂法、有机正电MMH处理剂法、电解质处理法、非离子型聚合物处理法、调整pH值法等。引起粘土矿物膨胀、分散的因素较多.除取决于组成粘土矿物组分和结构外,还与颗粒表面交换阳离子成分、分散介质性质等有关;粘土矿物的分散、膨胀、收缩、坍塌、渗透等特性均与ζ电位的大小有密切关系.因此,可用ζ电位的大小来判断粘土矿物的膨胀、分散性能及钻井液的抑制性能等。只要钻井液的ζ正电位高,对粘土矿物的抑制能力就强,就能达到稳定井眼、提高钻井速度、保护油气层、减少环境污染的目的。研究结果表明,无机盐具有压缩双电层的作用,交换阳离子价越高,水化膜越薄,ζ负电位越小,抑制性增强。反之,交换离子价越低.水化膜越厚,ζ负电位越高,分散性增强;阳离子处理荆具有提高钻井液ζ正电位的作用.能使粘土-水分散体系的电性发生反转;正电胶既可使粘土颗粒电性由负向正转化,又保持粘土-水分散体系的稳定性。通过对膨胀渗透理论与双电位理论研究,认为二者是统一的.

The causes for the inflation and dispersion of the clay minerals are analyzed, and the changing tendency of zeta potential of the clay minerals is investigated, with the electric property inversion methods for the clay minerals and drilling fluid also presented. There are many reasons causing the inflation and dispersion of the clay minerals, besides the composition and structure of the clay minerals, it is also related with the composition of surface exchanging cation and the characteristics of dispersing media. The dispersion, inflation, shrinkage, sloughing and permeability are all related with the magnitude of zeta potential, thus the magnitude of zeta potential could be used to estimate the inflation and dispersion of clay minerals and the inhibition of drilling fluid. The higher the zeta positive potential of drilling fluid, the stronger the inhibition of it on the clay minerals, thus the more beneficial for wellbore stability, ROP improvement, formation protection and pollution control. Research results show that the inorganic salt has the effect of compressing the electric double layer, the higher the valence of the exchanging cation, the thinner the hy-dration film, and the lower the zeta negative potential, the higher the inhibition; and in contrary, the lower the valency of the exchanging cation, the thicker the hydration film, and the higher the zeta negative potential, the higher the dispersion. The cationic additives have the effect of improving the zeta positive potential of drilling fluid, and invert the electric property of the clay-water dispersing system; the positive colloid inverts the electric property of clay particles from negative to positive, and also keeps the stability of the clay-water dispersing system. Studies on the inflation permeability theory and double electric layer theory show that the two theories are identical.