Experimental Study of the Chemical Stimulation of Iranian Fractured Carbonate Reservoir Rocks as an EOR Potential, the Impact on Spontaneous Imbibition and Capillary Pressure

Beside their worldwide abundance, oil recovery from fractured carbonate reservoirs is commonly low. Such reservoirs are usually oil-wet, thus, waterflooding leads into early breakthrough and low recovery due to the high conductivity of the fracture network, negative capillary pressure of the matrix and, consequently, the poor spontaneous imbibitions of water from fractures into the matrix during the course of waterflooding. In such problematic reservoirs, changing the wettability of the matrix toward water-wetness can improve spontaneous imbibition by changing the sign and, thus, the direction of capillary forces, resulting in an improvement of waterflood efficiency and, consequently, oil recovery. A study of this technique on. the most significant Iranian oil-producing reservoir, Asmari, seems necessary. Some surfactants of different ionic charges have been examined in this study. Asmari reservoir rock samples were used and the petrophysical and mineralogical properties of the rock samples were determined by both thin section analysis and core flooding techniques. Interfacial tension measurements have been done to decide surfactant solution concentrations. Capillary pressure measurements were conducted both before and after wettability alteration. Amott-Harvey and USBM wettability indices were determined. Among the surfactants, a cationic one could best raise the level of spontaneous imbibition. Favourable changes in the wettability indices were observed.