Abstract
The modeling of initial water saturation distribution in simulation models could be achieved by one of two techniques. The upscaling the log interpreted water saturation distribution of the finer 3D geological model constitutes the first technique. The challenge in this technique is to accurately describe the important rather thick transition zone of carbonate reservoirs. A large and non-achievable number of control points (wells) are needed. Rock type controlled restored state oil-brine capillary pressure, Pc, curves is the second technique. This results in an accurate picture of oil reserves providing that the rock types are distributed correctly. Significant numbers of oil-brine Pc measurements are needed however, to address all rock types, wettability, porosity and permeability ranges.
Frequently, not all the necessary Pc curves are available. To fill this gap, reservoir characterization data along with log-derived water saturation, Sw, data are utilized to generate representative Sw-height functions for all rock types of a carbonate oil reservoir. Only cored wells are employed, ensuring the most accurate rock-type profiles. To match the span of Sw at a given depth, sorting by porosity, permeability and reservoir quality index within each rock type is carried out. Describing the large span of log-derived Sw in the transition zone is especially challenging.
The technique assumes the log-derived saturations are correct and emphasize the need for laboratory tests of resistivity indices and cementation factors representative of the dominant rock types for accurate log interpretation.
The attainability of a good matching between the log-derived and the Pc-derived Sw and bulk volumes of water depth profiles for the cored and un-cored wells validated the modeling process. This is supported by statistical analysis and mapping of the water saturations in all layers of the simulation model.
