长链烷烃季铵盐DODMAC对钻井液中劣质固相的絮凝作用

Flocculation Performance of Long Chain Alkyl Quarternary Ammonium Salt DODMAC for Inferior Solid Phase in the Drilling Fluid

钻井液中亚微米颗粒含量对钻井液的性能影响很大,有必要研发有针对性的高效絮凝剂以清除钻井液中的亚微米劣质土,而尽量减少对膨润土等有用固相的絮凝。为实现上述目标,本文以高岭土和膨润土作为絮凝对象,通过Zeta电位、浊度分析、粒度分析和势能分析等方法,研究分析了长链烷烃季铵盐双十八烷基二甲基氯化铵(DODMAC)对钻井液中固相颗粒的絮凝效果及其絮凝机理。结果表明,质量分数0.2%高岭土分散液在pH=5附近达到等电位点,其表面电性及电量易受pH影响,而膨润土的电位相对更加稳定;DODMAC加量为42.86 mg/L时对高岭土颗粒的浊度去除率达到90%以上,继续增大加量后絮凝效果逐渐变差;而对膨润土的浊度去除率则随DODMAC加量的增加而增大,且在低加量下浊度去除率很低。通过调整DODMAC加量,可实现对劣质固相高岭土的选择性絮凝。DODMAC主要通过电性中和以及疏水絮凝作用降低高岭土颗粒势能,从而促进高岭土颗粒聚结絮凝,DODMAC加量过大后会使得高岭土颗粒表面电性发生反转且电位增大,导致高岭土颗粒间的静电斥力增大而易于分散;而在膨润土分散液中,DODMAC则通过吸附架桥方式作用于膨润土颗粒而促使其絮凝。

Solid content of submicron particles in drilling fluid has a great influence on the performance of drilling fluid. It is necessary to research targeted and effective flocculant to remove submicron poor solid and minimize the flocculation of useful solid such as bentonite. Using kaoline and bentonite as flocculation objects, the flocculation effect of the long chain alkyl quaternary ammonium salt, dimethyl distearylammonium chloride （DODMAC）, and the flocculation mechanism were investigated by the zeta potential, turbidity analysis, particle size analysis and potential energy calculation. The results showed that the kaoline dispersion reached the point of zero charge near the pH 5, and its surface electrical behavior and electric quantity were susceptible to pH, while that of bentonite was more stable. When the dosage of DODMAC was 42.86 mg/L, turbidity removal rate （TRR） of the kaoline dispersion was more than 90%, but it gradually decreased when the dosage was more than 42.86 mg/L. Meanwhile, the TRR of the bentonite dispersion gradually increased with increasing the dosage of DODMAC, moreover, the TRR was very low compared to that of kaoline dispersion. Therefore, the selective flocculation of kaoline could be achieved by adjusting the amount of DODMAC. DODMAC could reduce the energy barrier needed to overcome when kaoline occurred agglomeration and promote the agglomeration degree of kaoline particles through electric neutralization and hydrophobic flocculation. When the dosage of DODMAC was too large, the surface electrical behavior of kaoline particles would be reversed and the zeta potential would increase, which resulted in that the electrostatic repulsion between the kaoline particles increased and kaoline particles dispersed. As for the bentonite dispersion, DODMAC played an adsorption-bridging role in flocculation of the bentonite particles.