Integrated Rock Physics and Pseudo–Post‐Stack Simultaneous Inversion for Lithological Characterization and Hydrocarbon Prospectivity of the Najmah Formation in the Merjan Oil Field, Central Iraq

Abstract

This study integrates rock physics cross plot analysis, empirical velocity-density modeling, and pseudo-post-stack seismic inversion as three complementary analytical methods applied to a well-log and seismic dataset to identify lithological units and reservoir properties. The targeted reflector is the Najmah Formation, which was examined in well WK-1, in Merjan Oil Field, central Iraq, to demonstrate the effectiveness and precision of the proposed workflow.  First, to predict the lithology of the formation, three cross-plots were produced and interpreted using Density (RHOB) and Neutron Porosity (NPHI) logs as color scales: Vp/VS versus acoustic impedence, RHOB versus Gamma Ray, and Lambda-Rho versus Mu-Rho. In addition, a two-dimensional probability density function (PDF) approach was employed to quantify density distribution and identify the most prospective reservoir interval. Second, based on density and velocity logs, a local polynomial equation was derived for the Najmah Formation, lying below the Nafe–Drake equation curve. Third, a pseudo-post‐stack simultaneous inversion technique was applied to support the identified reservoir units within the lower part of the Najmah Formation. The inversion results demonstrated strong agreement with the rock-physics interpretation, with potential reservoir zones exhibiting relatively low acoustic impedance values, reflecting favorable porosity and potential hydrocarbon saturation. In contrast, higher acoustic impedance values were observed in intervals dominated by compacted dolomite and tight limestone, confirming their non-reservoir characteristics. This agreement highlights the reliability of the integrated approach in accurately delineating lithological and reservoir properties.