Wettability Alteration of Carbonate Rock by Chelating Agents and Viscoelastic Surfactants: Synergetic Impact

In enhanced oil recovery, surfactants are injected to recover the residual oil by reducing the oil/water interfacial tension or by altering the wettability of the rock. Viscoelastic surfactants are a special class of surfactants that can also control mobility due to their viscoelastic nature, in addition to lowering interfacial tension. However, detailed studies of wettability alteration by viscoelastic surfactants are still needed. Chelating agents have recently gained attention as an alternative to low-salinity water in enhanced oil recovery due to their capability to capture metal ions. This study used the contact angle measurement to investigate the synergetic impact of chelating agents and viscoelastic surfactants on the wettability alteration of carbonate rock. The wettability alteration performance of a viscoelastic surfactant (VES) and five chelating agents in deionized water, synthetic seawater, and diluted synthetic seawater solutions was studied. Their wettability alteration performance was compared by contact angle difference before and after soaking oil-wet Indiana limestone samples in the chelating agent solutions. Results showed that all tested chelating agents exhibit strong wettability alteration performance in deionized water solution. Increased salinity impairs the wettability alteration performance due to the consumption of chelating agent molecules by metal ions. The studied VES has weak wettability alteration performance when dissolved in synthetic seawater alone. Solutions combining VES and chelating agents, however, exhibited moderate to strong wettability alteration performance. With the addition of the chelating agent into VES solutions, the salinity tolerance and wettability alteration performance are significantly improved. The optimum formulation of viscoelastic surfactant and chelating agent changed the wettability from strongly oil-wet (163.0 degrees) to water-wet (64.2 degrees). The wettability alteration by VES and chelating solutions is a gradual process and could be further enhanced at reservoir temperature.

Automated summary

This study investigated the synergetic impact of chelating agents and viscoelastic surfactants on the wettability alteration of carbonate rock using contact angle measurement. The results showed that all tested chelating agents exhibited strong wettability alteration performance in deionized water solution. The combination of viscoelastic surfactant and chelating agents demonstrated moderate to strong wettability alteration performance. The optimum formulation of the two changed the wettability from strongly oil-wet to water-wet.