Determining Wettability of Fractured Carbonate Reservoirs

Abstract

Wettability plays a pivotal role in oil recovery processes in reservoirs owing to the fact that it has a direct impact on the proportion of oil recovery. Reservoir rocks are a complex of a variety of mineral types, and each mineral may have a different wettability. Typically most aquifer materials such as quartz, carbonate, and dolomite are water-wet prior to oil migration. Some oil recovery processes are designed to alter the wetting preference of the oil formation to be more oil-wet. There are three techniques used in the laboratory for the characterization of the capillary pressure properties of core samples: mercury injection, centrifuge, and porous plate. This article provides an in-depth review of wettability. It also entails a case study from one of the Iranian carbonate reservoirs and measurements, which have been carried out for selected samples to clarify the nature of the wettability of reservoir rock. Samples were chosen from three wells of oil field which is composed of limestones and dolomites, rarely inter-bedded by shales, and their wettability was measured by Amott–Harvey method, which is one of the main methods for measuring wettability. After cleaning and drying the samples, measurements were carried out. According to the results, it can be said that the range of Amott–Harvey index for these samples is between −0.48 and −0.8. In Amott–Harvey method, if IAH varies from −1 to −0.3, the rock is oil-wet. Therefore, it can be concluded that the reservoir is oil-wet.