Wettability estimation of low-permeability, siliceous shale using surface forces

This work evaluates shale/oil wettability and wettability alteration by solutions whose pH ranges from 3 to 12. The reservoir rocks are siliceous shale that are fractured and low permeability oil-bearing rocks. Wettability alteration is evaluated in terms of estimated thin-film stability, contact angle, and fines migration. Previously, we presented core-scale spontaneous countercurrent imbibition and forced displacement results for the crude oil/brine/rock system. The new surface forces results for stability of wetting films and contact angle compare favorably to the previously measured Amott index to water. The pH = 3 and pH = 12 solutions result in greater water wettability in comparison to neutral pH brine. The possibility of fines migration, that is one of the scenarios of wettability alteration, is explored. Results show that a balance of the surface forces as a function of brine chemistry explains wettability alteration of these siliceous shale samples. The trend of small contact angles for the aqueous phase for basic and alkaline solutions is consistent with the oil recovery characteristics, and fines migration does not trigger wettability alteration for this particular crude oil/brine/rock system.