Abstract:

There is a very prominent problem of water sensitive damage and liquid trap damage caused by drilling fluid during the exploitation process of shale gas reservoirs. A two-step dilution method for preparation of oil-in-water nanoemulsions used for the protection of shale gas reservoirs was introduced. The nanoemulsion could have small droplet sizes and fine dispersity. Selecting mixtures composed of Gemini hyamine surfactant GTN, Tween80 and n-butyl alcohol as surfactant component (referred to as S+A), the effects of mass concentration of NaCl on the properties of NaCl solution/(S+A)/n-octane systems was studied. The influence of the phase inversion temperature, emulsification methods and the structure of microemulsion on the droplet size of nanoemulsion was investigated. The instability mechanism of nanoemulsion system was researched. The results showed that increasing the concentration of NaCl could effectively change the microemulsion structure of NaCl solution/(S+A)/n-octane system, decrease the phase inversion temperature significantly and improve the emulsification efficiency. Oil-in-water nanoemulsions prepared by two-step dilution method had the smallest droplet size and the best dispersity at R_os 7:3 when the emulsification temperature approached the phase inversion temperature. The mechanism of instability can be attributed to Ostwald ripening in NaCl solution/(S+A)/n-octane system. Nanoemulsion had good performance for protecting shale gas reservoirs.

Key words: nanoemulsion, microemulsion, surfactants, Ostwald ripening, interfacial tension, petroleum

摘要：

针对钻井液滤液侵入页岩储层极易导致严重的水敏损害及液相圈闭损害问题,采用两步稀释法研备出粒径极小、分散性好且长期稳定的页岩储层保护用水包油(O/W)纳米乳液。选取Gemini季铵盐型表面活性剂GTN、Tween80与正丁醇三者复配作为表面活性剂组分(记为S+A),通过室内实验研究了水相中NaCl质量分数对NaCl溶液/(S+A)/正辛烷体系微乳液特性的影响,考察了微乳液相转变温度(PIT)、制备方法及其微观构型等因素对采用两步稀释法制备的纳米乳液粒径的影响,同时对纳米乳液体系的失稳机理进行研究。结果表明,NaCl溶液/(S+A)/正辛烷体系微乳液中NaCl的加入可以显著提高表面活性剂组分的乳化效率,改变微乳液微观构型,使PIT显著降低;当剂油体积比(R_os)为7:3时,通过调节双连续微乳液的PIT接近实验乳化温度,采用两步稀释法制备的O/W纳米乳液粒径最小且分布范围最窄;NaCl溶液/(S+A)/正辛烷体系纳米乳液主要失稳机理为奥氏熟化;纳米乳液具有良好的储层保护作用。

关键词: 纳米乳液, 微乳液, 表面活性剂, 奥氏熟化, 界面张力, 石油