Application of Post Stack Acoustic Impedance Inversion to Lateral Rock Property Prediction: A Case Study Eti-field Offshore Niger Delta

Abstract

This study presents the result of a Model-based seismic inversion technique which was used to invert an acoustic impedance structure within a reservoir interval by intergrating well logs and 3D post stack seismic data obtained from Eti-field offshore Niger Delta. The purpose was to delineate lateral and vertical alternations in subsurface rock properties which is caused by difference in lithofacies within the reservoir interval. This would help to define hydrocarbon fairways better and constrain the range of hydrocarbon zones for field development. The inversion workflow used in this study includes forward modelling of reflection coefficients from a low frequency impedance model driven from well logs and convolution of the reflection coeffiecients with a source wavelet derived from the seismic data. P-impedance inversion analysis at the control well location gave a near perfect correlation of 0.993686 (correlation coefficient of ≈ 99.4 %) between the original P-impedance log, initial guess P-impedance model log and inverted P-impedance log. The estimated error observed was 5533.1 which corresponds to (0.112308) about 11.23 %. Seismic inversion analysis realized an acoustic impedance striucture with P-impedance values ranging from 7000 to about 50000 ft/s*g/cc and having a general increase with depth trend. Impedance slice extracted from the impedance volume at top of the reservoir predicted lateral variations in P-impedance at well control and away from well control. This information can be invaluable in delineating more prospective reservoir zones in the field and thereby enhancing optimum field development which aids in reservoir management decisions.