indicator. The substrate cut taken from the core plug was saturated with crude oil at Swi, as explained previously. To obtain a smooth surface, the substrate cut from the Berea sandstone was sanded with sandpaper. The substrates were loaded into the oven to be dried and were then treated with air to remove the minerals' fines. The substrates were then attached to a glass sheet by glue and installed in the test chamber. The desired fluid was then poured into the chamber until the substrate was immersed. The contact angle was then measured after an hour stabilization of the oil droplet on the substrate.