Mixed wettability is a common concern in heterogeneous reservoirs. The problem from a practical point of view is the general lack of water saturation exponent (n) laboratory values in rocks with mixed wettability.

To contribute to the solution of this concern, we utilize electromagnetic mixing rules to develop a new petrophysical model capable of estimating the water saturation exponent (n) and water saturation (Sw) in heterogeneous reservoirs with mixed wettability. The reservoirs are represented by dual porosity (matrix and fractures or matrix and isolated porosity) and triple porosity (matrix, fractures, and isolated porosity) models. Results from the models developed in this work compare well with core data.

We have used the same electromagnetic mixing rules in the past for successful determination of the porosity exponent (m) in heterogeneous reservoirs. The addition in this paper offers a means for calculating the water saturation exponent (n) and makes the electromagnetic mixing rules a powerful tool for complete formation evaluation of heterogeneous reservoirs with complex pore structures and mixed wettability.

It is concluded that the new petrophysical models developed in this study provide a significant contribution to the determination of water saturation exponent (n) and water saturation (Sw) in rocks with mixed wettability and hence lead to improved values of hydrocarbon in place estimates.

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