Wettability evaluation of Iranian carbonate formations

The evaluation of wettability of carbonate rock samples of Iranian formations has been investigated using relative permeability curves and Amott tests. The experiments have been performed at both ambient and reservoir temperature to study the temperature effect on wettability evaluation of carbonate rocks. The samples were carefully cleaned and aged at reservoir temperature in order to achieve restoration of reservoir wettability. Petrophysical properties of each sample were measured using both thin section and core flooding techniques. thology of the samples consists of both dolomite and limestone. The qualitative evaluation of wettability on carbonate samples using relative permeability curves showed that there was a discrepancy between the results from the rules of end point and those from the rule of crossover saturation. The crossover saturations in relative permeability tests at reservoir temperature showed more oil wetness in comparison to tests at ambient temperature. Quantitative experiments by the Amott method using a core flooding system showed that carbonate samples were oil-wet when the tests were performed at reservoir temperature. However, the samples had intermediate wettability characteristics when the tests were performed at ambient temperature. All the Amott tests at reservoir temperature were repeated using an ultra-centrifuge. The results with the latter method suggested intermediate wettability characteristics, compared to oil-wet results obtained from the core flooding tests. Centrifuge experiments also produced capillary pressure curves that were used to evaluate the wettability according to the method of U.S. Bureau of Mines (USBM).