Determination of shale type in shale formation has long been a difficult task. Presence of shales in some of the Iranian reservoir formations are one of the most important subject. Shale types have to be considered, because existence of shale type reduces, effective porosity and permeability of the reservoir to some extent. Allogenic Shale is distributed in formations in three basic types, Dispersed, Laminar and structural. Each of these shale types has different effect on porosity, permeability and water saturation. Dispersed shale type reduces effective porosity and permeability to a great extent, but, laminar and structural have less effect on petrophysical parameters. In this investigation, shale types, Shale volume and effective porosity of shale formations have been determined from well logs based on cross-plotting. In other words, a triangle Density-Neutron cross-plot is used to determine the above parameters. The area of study chosen from central oil fields of Iran, where some of the wells are used (Tabnak Field). Tabnak Well C selected for this study in Kangan Formation, South Pars. This study illustrates that distribution of shale types in Kangan Formation is mainly dispersed shale with few of laminar shale, and the quality of effective porosity (φ e ) decreases with increasing depth in the Kangan Formation.