Wettability alteration in chalk: 1. Preparation of core material and oil properties

A reproducible method has been developed to create homogeneous oil-wet chalk material wettability with and without initial water saturation. This was accomplished by aging crude oil-saturated chalk cores for different time intervals and at different temperatures. A total of five different crude oils were tested for their potential to alter the wetting properties of the chalk material. Chemical analysis of the crude oils showed that the potential for wettability alteration correlated with the amount of acidic components in the crude oil, as measured by their acid number (AN). The wettability of the chalk was evaluated by their ability to spontaneously imbibe synthetic brine. There was no sign of water imbibition into cores without initial water saturation after 5 weeks, while cores with an initial water saturation of 23% imbibed about 9% of water during 8 weeks at 40°C.