TUNING ANALYSIS FOR THIN BEDS USING AMPLITUDE VARIATION WITH OFFSET (AVO) AND SPECTRAL DECOMPOSITION OVER “SAA FIELD”, NIGER DELTA

Abstract

Tuning analysis for thin beds using Amplitude Variation with Offset (AVO) and spectral decomposition have been carried out in a field, offshore Niger DeltaGamma ray and resistivity logs were used for lithology and fluid identification. Well-to-seismic tie was generated from sonic and density logs. AVO was carried out using partial stacks of near, mid and far angles. This was done using Hampson Russell software version 10.2. Spectral decomposition analysis was done using the fast fourier transform method. The stratigraphy is alteration of sand and shale lithologies. The delineated reservoirs lie within a depth interval of 1,800 3,640 m subsea. Crossplots of logs and seismic data reveal gas, oil, water, sand and background of shale. Also, shallow gas sands were mapped at shallow depths. Analysis from gradient and intercept crossplots revealed a class III AVO gas sand. Compressional and shear wave impedance maps and sections derived from the inversion process predicted the lateral extent of reservoirs and also aided in fluids and lithology discrimination. Spectral decomposition and inversion resolved thin beds that were not mapped from seismic data. The beds were beyond the resolution of seismic data and located at a depth interval of 2,180 2,545 m subsea.