Determination of Wettability of Iranian Carbonate Reservoir Rocks in Restored-State

Many special core analyses, including capillary pressure, relative permeability, and water flooding efficiency are affected by the wettability of the core. In order to achieve reliable results, experiment must be performed on preserved or aged sample. Considering the importance of wettability factor in special core analysis data and their fundamental roles in reservoir studies, the present work was defined to search for wettability characterization of some Iranian carbonate formations. Samples were carefully cleaned and aged at reservoir temperature in order to prepare the restored conditions. Experiments were run at 90 °C with crude oil and formation water. A period of 40 days was allowed for aging with crude oil. Petrophysical properties of each sample were measured using both thin section and core flooding techniques. The lithology of the samples consists of both dolomite and limestone. The qualitative evaluation of carbonate samples using relative permeability curves showed that there was a discrepancy between the result from the role of end-points and those from the role of cross over saturation. The cross over saturations in relative permeability tests at reservoir temperature showed that samples were oil wet. The Amott and USBM tests have been run on samples in a combination procedure. The capillary pressure curves obtained by the centrifuge method were used in order to calculate the USBM wettability index. Quantitative results by the Amott method showed that most carbonate samples had intermediate wettability characteristics, but the results from combined Amott-USBM testing indicated that system is mostly oil-wet. Centrifuge experiments also produced capillary pressure curves that were used to evaluate the wettability are according to the method of U.S. Bureau of Mines.