SEISMIC ATTRIBUTES ANALYSIS AND PRE-STACKED INVERSION FOR RESERVOIR CHARACTERIZATION IN ‘HUNTER’ FIELD, OFFSHORE, NIGER DELTA

Abstract

Attributes from Pre-stack seismic analysis are a crucial aspect in reservoir characterization as they help to analyse and predict lithology and fluid parameters for Direct Hydrocarbon Indicators. This study aims to improve the characterization of lithology and fluid content using Seismic attributes analysis and inversion technique for well placement optimization. Three (3) Well logs and pre-stacked seismic data, from Hunter field offshore Niger Delta, were used. Petrophysical parameters were computed from Well logs and used to predict the shear wave velocity for each of the wells, using the Gassmann fluid substitution technique. A Cross-plot Analysis of the Velocity Ratio vs Acoustic Impedance was used to generate the lithology log which was used to predict the lithology across the study area. Seismic Attributes, namely the Scaled Poisson’s Ratio and the Fluid Factor, were derived from pre-stack seismic data. The integration of inversion results enhanced the prediction of possible prospects away from well control locations and justifying well placement possible. Four (4) zones of interest (sand) were delineated and Petrophysical parameters - porosity, volume of shale, and water saturation were derived for each reservoir. The values ranged from 29% to 36%, 3.70% to 10.40% and 10% to 28% respectively. The results of the Pre-stack Attribute and Seismic Inversion Analysis showed possible Prospect areas at the centre on slice 1, on slice 2 along the western region, on slice 3 along the north-eastern region, and slice 4 along the southern region. These identified prospects were characterized by high Fluid Factor values, high Poisson’s Ratio indicating the top of the reservoirs, and low Acoustic impedance which mimics the signature of hydrocarbon sand. The study has been able to use both Pre-stack seismic Attributes and Seismic Inversion in predicting parameters away from the control points which help to identify new prospects in the study area which help to properly map reservoirs.