Reservoir Units of Yamama Formation in Gharafoilfiled, Southern Iraq

Abstract

Reservoir unit classifications can be used in reservoir characterization of carbonate reservoirs where there is variability in the distribution of petrophysical properties. This requires the integration of geological and petrophysical data at different scales. In this study, cores and thin sections from Yamama Formation (Lower Cretaceous) at Gharaf oilfield, southern Iraq, were studiedto identify reservoir units.

     Ninereservoir units (units Y1 to Y9) were identified based on petrophysical evaluation by using interactive Petrophysics program (IP) software and depositional environments and related microfacies.The unit Y2 have the highest reservoir quality, which consists of grain-supported facies(packstone and grainstone) characterized by high values of effective porosity and oil volume.The second important reservoir unit is unit Y7 where oil exists in wells Ga-1, Ga-4, and Ga-5. By contrast, the unit Y6 is identified with no observable reservoir quality due to low porosity of mudstone microfacies. The computer processes interpretation (CPI) results show that unit Y1 has poor petrophysical properties except in wells Ga-3 and Ga-4 where reservoir properties are enhanced by fractures. Other units are characterized by different degrees of reservoir quality, and they are differentiated in terms of effective porosity, water saturation, clay volume, and facies types.