Determination of Shale Volume, Shale Types and Effective Porosity Based On Cross Plotting

Abstract

The evaluation of shaley formations has long been a difficult task. Presence of shale and shale types in some of the Iranian formations are one of the most important factors. Shale types have to be considered, because existence of shale reduces, porosity and permeability of the reservoir to some degree. Shale Distributed in formations in three basic types, Dispersed, Laminar and structural. Each of these shale types has different effect on porosity, permeability and saturation. Dispersed shale reduces porosity and permeability to a great degree, but, laminar shale and structural shale have little effect on petrophysical parameters. In this investigation, shale types, Shale volume and effective porosity of Kangan Formation have been determined from well log data and compared with crossplotting. In other words, a triangle Density-Neutron cross-plot is used to determine above parameters. The area of study lies in central oil fields of Iran, where one of the well is used (Tabnak Well C). Tabnak Well C selected to study Kangan Formation from Iranian oil field, in Pars onshore. This study illustrates that distribution of shale types in Kangan Formation is mainly dispersed shale with few of laminar shale, and percentage of effective porosity (φe) decreases with increasing depths for Kangan Formation.