A method has been developed to infer the wettability of steam-water-rock systems based on the relationship between permeability and capillary pressure by Purcell. The Purcell model was extended to two-phase flow to verify whether the wettability is a function of water saturation. The results calculated using the experimental data showed that the wettability index in the drainage process was greater than that in the imbibition. The corresponding contact angle in drainage was smaller than that in imbibition, which is realistic and consistent with the existing experimental results in capillary tubes. Both the receding (drainage) and advancing (imbibition) contact angles in steam-water-rock systems were reasonably independent of water saturation ranging from about 25 to 85%. It was also found that the wettability model could be reduced to the model reported by Slobod and Blum (1952) in specific cases. The method developed in this study to estimate wettability of steam-water-rock systems could be applied directly to other gas-liquid-rock and liquid-liquid-rock systems.

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