无机离子在油基泥浆所引起储层润湿反转过程中的作用

THE ROLE OF INORGANIC IONS PLAYED IN THE WETTABILITY REVERSAL OF RESERVOIR ROCKSCAUSED BY OIL-BASED MUDS

以实验方法研究了地层水中Na^+和Ca^2+等无机阳离子与油基泥浆的协同作用对油藏岩石润湿性的影响。研究结果表明,离子浓度的增加使砂岩孔隙表面的水湿性减弱或油湿性增强,在相同浓度下多价离子的影响大大超过单价离子的影响。并且发现这种影响主要发生在无机离子与阴离子型表面活性剂共存的体系中,无机离子通过改变界面电性使水膜稳定性减弱,从而导致活性剂在固体表面的吸附量增加并改变其离子的排列方向。无机离子对阳离子烈表面活性剂的润湿作用影响较小。

The synergetic effect of inorganic ions, such as Na^+and Ca^(2+)present in the formation water, and in the filtrates of oil-based muds on the wettability of sandstone cores has been studied. The Amott/USBM method was used to measure wettability changes. The water wettbility of pore surface of sandstone cores reduces (or oil wetability rises) with the increase in ion concentrations. Under the condition of the same concentration, the effect of multi valentions greatly surpasses the effect of monovalent ions, The effect of inorganic ions on the wettability of sandstone is shown mainly for system in which both inorganic ions and anionic surfactants are present. In this system, the inorganic ions tend to reduce the stability of the thin water film existed between the rock and oil because they strongly affect the surface charges on the rock surfaces and water/oil interfaces. Thus, they will cause an increase in the amount of surfactants adsorbed on the sandstone surface, and a change in the configurations of the surfactants as well. The inorganic ions have only a slight effect on the wetting behavior of cationic surfactants.