It is a modified sodium sulphonated asphaltic compound.
Sulphonated asphalt is a combination of Gilsonite, blown asphalt, lignite and causticsoda.
It uses to the stability of drilling fluids and stabilizes well wall.
Sulphonated asphalt Improves lubricity thereby reducing torque and drag of the drilling string.
And also Prevents bit and down hole assembly bailing by preferentially oil wetting the drill string and Controls high temperature water loss.
It can Reduces High Temperature and High Pressure Fluid Loss and Improves Filter cake Quality and helps seal micro fractures.
Note the physical properties of sulphonated asphalt in the table: