An Empirical Saturation Modeling of a Complex Carbonate Abu Dhabi Reservoir Using the Routine High-Pressure Mercury and Oil/Water Capillary Pressure Data

Abstract

Abstract Minimizing uncertainty associated with predicted log water saturation can be best achieved through the integration of log analysis (formation evaluation) and capillarity (core measured high pressure mercury and oil/water drainage capillary pressure data). Further reduction of uncertainty in predicted formation water saturation requires; first the most probable log porosity solution interpretation; second the most probable log porosity/permeability relationship (match core measured values); and third a quantitative capillary pressure model that represents measured high pressure mercury and oil/water drainage capillary pressure data. In this paper, the classical Leverett-J method (Leverett 1941) was used in the integration of capillary pressure data with routine core analysis and petrophysical rock types to generate a robust model for predicting formation water saturation profiles. The classical interpolation method that relates capillary pressure (derived from Leverett J function) to water saturation has been used predict the wetting phase saturation. The assignment of capillary pressure curves to their corresponding rock types was accomplished by grouping rock types according to discrete ranges of the interval speed which is defined as the square root of core measured permeability divided by porosity (k/φ) data. Each range of the interval speed will have a corresponding Leverett J function from which water saturations will be interpolated according to its respective height above the Free Water Level (FWL) (using the log predicted permeability-porosity ratios). In the absence of clear fluid contact, a trial and error method is used to adjust the FWL until a good agreement between the log predicted water saturation and the predicted water saturation from the capillary pressure correlation is reached. The error in averaging was minimized by increasing the number of rock types (minimizing the ranges of interval speed) using a large number of measured high pressure mercury and oil-water drainage capillary pressure data. Furthermore, this paper presents a comprehensive comparison of the log derived and model predicted water saturations.