A Comparative Study of Acoustic and Elastic Impedance Seismic Models for Rock Property Prediction: An Example from XYZ Field, Nigeria

Abstract

A comparative case study of acoustic and elastic impedance seismic inversion for reservoir litho-fluid delineation in XYZ field, Nigeria is presented. The well studied has four reservoirs. Acoustic impedance inversion carried out on near angle stack was successful in showing the tops of three reservoirs and their lateral extents, but failed to successfully delineate the top of the major reservoir. Fortunately, a shear sonic log was acquired in the well, and a far angle PSTM stack was available for the field. Combining the shear sonic log with the available compressional sonic and density logs, an elastic impedance log was generated at 36⁰, corresponding to the incidence angle for the far offset stack, and was used to invert the far angle stack for elastic impedance. The elastic impedance inversion was successful in showing the major reservoir zone as well as clearly delineating its top and lateral extent. It was observed that the acoustic impedance log used for inverting the near angle stack was near constant through the top reservoir transition and this may have accounted for the failure of the acoustic impedance inversion to delineate the top and lateral extent of the reservoir. This paper focuses on comparing the results of the inversions targeted at the main reservoir, highlighting possible reasons for failure and success of the individual inversion method.