A review of petrophysical relationships for estimation the volume of clay, Case study: Shurijeh reservoir Formation in an eastern Kopet-Dagh basin field

Erroneous estimation of clay volume can result in miscalculation of reservoir parameters such as effective porosity and water saturation which finally leads to false interpretation of reservoir production. Thus, volume of clay (Vcl) is the most critical parameter to determine in shaly sand reservoir quality assessments. In this study, volume of clay in Shurijeh Formation, aging Lower Cretaceous, was estimated after carrying out a sensitivity analysis between a suite of petrophysical logs and laboratory measure volume of clay, using seven different petrophysical methods from six types of well logs and combination of some of them. On each method different petrophysical corrections (such as 0.6-coefficient, Larinov-1, Clavier and Steiber) were applied and then the results were compared to the results of quantitative analysis of 76 core samples from produce well (A) and non produce well (B) in one of eastern Kopet-Dagh basin fields. Finally, based on minimum average relative error, the best log and the best correction are determined as gamma ray log and Steiber correction for volume of clay estimation in this formation. Also, an empirical equation was developed based on index of gamma ray method for evaluating the volume of clay which has the minimum relative error.