USI is determined as the accumulative volume in mililiters of aqueous phase separated in 30 min from the test emulsion formed from 5 mL aqueous solution of a chemical agent and 5 mL crude oil.

• 以实验温度下5mL化学剂水溶液与5mL原油形成的乳状液在30min内累计分出的水相体积(以毫升计)表示USI。