Effects of Lithological Variation and Petrophysical Parameters on Oil Potential of the Ilam Reservoir (Upper Cretaceous), Ahvaz Oil Field, SW Iran

Petrophysical and lithological parameters study of Ilam reservoir in Ahvaz oil field is the main aim of the present research work. Ilam Formation consisted lithologically of limestone, dolomitic limestone, and less quantity of scattered shales. Facies changes are also observed through the formation. On the basis of petrophysical parameters distribution the reservoir divided into 4 zones. The results indicated that shale volume calculated by CGR log, as a shale index, is less than 10% and so the Ilam reservoir is clean formation. Shale quantity is low in zones 2 and 3 than zones 1 and 4. However, the shale volume is very less but its effect on petrophysical parameters especially porosity and permeability is intense. The Ilam Formation is estimated to have 26.8 % water saturation and 3.3% of irreducible water saturation. Middle part is characterized by low rate of water saturation compared to other parts and along with effective porosity average in the range of 14.7%. Calculated permeability average is 8.3 mD. Permeability variation is indicating a direct relation with the porosity. All these results are emphasized that the middle part (zones 2 and 3) is in better condition in view of oil potential and hydrocarbon reserve in comparing to other parts.