TITLE:
The Impact of Model Based Offset Scaling Technique on the Amplitude Variation with Offset Responses from 3D Seismic Data Acquired from the Tano Basin, Offshore Ghana
AUTHORS:
Striggner Bedu-Addo, Sylvester Kojo Danuor, Aboagye Menyeh
KEYWORDS:
Amplitude Variation with Offset (AVO), Model Based Offset Scaling Technique, Tano Basin
JOURNAL NAME:
International Journal of Geosciences,
Vol.15 No.1,
January
31,
2024
ABSTRACT: Amplitudes have been found to be a function of incident angle and offset. Hence
data required to test for amplitude variation with angle or offset needs to
have its amplitudes for all offsets preserved and not stacked. Amplitude
Variation with Offset (AVO)/Amplitude Variation with Angle (AVA) is necessary
to account for information in the offset/angle parameter (mode converted S-wave
and P-wave velocities). Since amplitudes are a function of the converted S- and
P-waves, it is important to investigate the dependence of amplitudes on the
elastic (P- and S-waves) parameters from the seismic data. By modelling these effects for different reservoir
fluids via fluid substitution, various AVO geobody classes present along the
well and in the entire seismic cube can be observed. AVO analysis was performed on one test well (Well_1)
and 3D pre-stack angle gathers from the Tano Basin. The analysis involves
creating a synthetic model to infer the effect of offset scaling techniques on amplitude responses in
the Tano basin as compared to the effect of unscaled seismic data. The spectral balance process was performed to
match the amplitude spectra of all angle stacks to that of the mid (26°) stack
on the test lines. The process had an effect
primarily on the far (34° - 40°) stacks. The frequency content of these stacks
slightly increased to match that of the near and mid stacks. In offset scaling
process, the root mean square (RMS) amplitude
comparison between the synthetic and seismic suggests that the
amplitude of the far traces should be reduced relative to the nears by up to
16%. However, the exact scaler values depend on the time window considered.
This suggests that the amplitude scaling with offset delivered from seismic
processing is only approximately correct and needs to be checked with well
synthetics and adjusted accordingly prior to use for AVO studies. The AVO attribute volumes generated were better at resolving anomalies on
spectrally balanced and offset scaled data than data delivered from
conventional processing. A typical class II AVO anomaly is seen along the
test well from the cross-plot analysis and AVO attribute cube which
indicates an oil filled reservoir.