Lithology Evaluation of Nahr Umr Formation Using AI with Vp/Vs relationship at Amara Oil Field, Southern Iraq

Abstract

The litholog of Nahr Umr Formation was evaluated using the Acoustic Impedance (AI), Vp/Vs ratio cross plot colored by petrophysical properties (Vsh, PHIT, PHIE, and Sw) in Am-6-Am-10 wells. Bulk density is an important physical property that reflects matrix density and fluid density that exist in rocks pores. It is used as the main parameters to estimate physical characteristics (porosity, water saturation, shale volume, and others). AI was calculated using RHOB and VP logs. Shear velocity was calculated using Greenberg Castagna equations used for estimating the Vp/Vs ratio and the result Showed that the Nahr Umr Formation is composed of two main lithological units. The upper unit (depth 3540m -3672m) is composed of limestone (limestone with low shale volume and low porosity high AI and limestone with high shale volume of high porosity and low AI), while the lower unit (depth 3672m-3740m composed of sandstone with a high volume of shale have the lower AI value. The type of fluid was high water saturation in the carbonate part with low effective porosity and hydrocarbons existing in the sandstone part with lower acoustic impedance value.