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 Ros 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.