Characterizing Carbonate Rock Wettability by Washburn Contact Angle Method with Surfactants

Washburn contact angle method was developed to measure the wettability of rock powder. The main objective is to identify the solid surface wettability accurately and faster using crushed rock powder. Conventional methods to quantify the solid surface wettability are either to measure the contact angle on core slice or to measure the wettability index of the whole core. For optical contact angle method, when there is ultra-low interfacial tension between crude oil and surfactants, oil drop tends to spread on the core surface, making the contact angle measurement impossible. The wettability index method is usually time-consuming. Using Washburn method, the average wettability property of crushed rock powder can be precisely determined. By controlling the powder particle size and packing density, the measurement of contact angle is reproducible. A number of tests were conducted using this method to study the effect of surfactants on the wettability of solid surface. The results showed that anionic surfactants can alter the mixed-wet and oil-wet carbonate powder to more water-wet. This method serves as a fast way for the evaluation of rock wettability and the wettability alteration induced by chemicals.