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In this paper we will discuss about the development shaly models by using effective porosity versus true specific resistivity cross-plots, which are affected by the shale group (Ash) in three states: layer, dispersed and total shale. By these methods we
can get a realistic idea about the oil reservoir with natural fracturing.
The response of equations of aforesaid models prepares some cross plots to calculate the percentage of water saturation. In the proposed methods there are three important parameters including:
1. Porosity parameter (m), which should not be considered equal to 2 and must be determined by trial and error.
2. Specific resistivity of water (R",), which is measurable in the water-bearing reservoir.
3. All the analyzed shaly layer can be presented in the cross plots contain porosity, specific resistivity affected by the shale group (Ash), even if shale volume changes monotonous and continuous.
At the end, we discuss about two case studies by using Cross plots which are very useful tools in analysis and evaluation of the layer, dispersed and total shaly models.