Impacts of petrophysical properties of sandstone reservoirs on their irreducible water saturation: Implication and prediction

Irreducible water saturation (S-wir) is an important parameter in reservoir evaluation that can affect hydrocarbon saturation, permeability prediction models and estimation of original oil in - place. The S-wir is usually obtained from capillary pressure data. In this study, routine and special core analyses for sandstone reservoirs in four wells were used to investigate the relationship between irreducible water saturation and the petrophysical properties of the reservoir rocks. The results indicated that the magnitude of S-wir is controlled by a complex relationship of reservoir rock wettability, reservoir quality, clay content, clay mode of distribution, and capillary pressure. Reservoir rock wettability can obscure the effect of other factors in the case of oil-wet rocks. On the other hand, irreducible water saturation from published data were used together with the studied four wells data, providing 110 sandstone samples covering different geologic ages and fades, to examine the applicability of the traditional empirical models that were commonly used in S-wir prediction as well as to introduce a new simple equation by which S-wir can be predicted. The study indicated that the Timur equation gave the best applicable empirical model to predict S-wir. The study indicated also that the flow zone indicator can slightly improve the prediction strength of the S-wir. Using other parameters characterizing capillary pressure curves such as displacement pressure and Swanson parameter didn't improve the relationship prediction strength.