Assessment of Shale Volume Estimation Using Non-Linear Approaches for Jeribe Formation in Jambour Oil Field, Northern Iraq

The Jeribe Formation is a naturally fractured carbonate reservoir, mainly composed of limestone and dolomite rocks, with about 40 m of thickness. This formation is a productive reservoir in the Kirkuk region, north of Iraq. Because the current area of study lacks accurate formation evaluation, this study aims to determine the petrophysical properties of the main reservoir. The first crucial step toward achieving this goal is determining the volume of shale. Earlier studies implied a linear model for the determination of the gamma-ray index. However, current evidence about the formation indicates the occurrence of asphaltene and high water salinity. Therefore, the hypothesis of using a linear model is not valid for determining the volume of shale. Consequently, the study suggests using three different non-linear models, namely, the Larionov, Stieber, and Clavier models, and comparing the results with the one obtained from the linear model. Three wells are selected from the northern part of the Jambour field to evaluate the Jeribe Formation. The results from all the wells indicated that the Larionov model is the most suitable for determining shale volume and that the presence of asphaltene and high water salinity affects the gamma-ray log. The non-linear models are more appropriate for future petrophysical evaluation of the Jeribe Formation.