The study involved the
evaluation of the hydrocarbon potential of FORMAT Field, coastal swamp depobelt
Niger delta, Nigeria to obtain a more efficient reservoir characterization and
fluid properties identification. Despite advances in seismic data interpretation
using traditional 3D seismic data interpretation, obtaining adequate reservoir
characteristics at the finest level had proved very challenging with often
disappointing results. A method that integrates the amplitude variation with
offfset (AVO) analysis is hereby proposed to better illuminate the reservoir.
The Hampson Russell 10.3 was used to integrate and study the available seismic
and well data. The reservoir of interest was delineated using the available
suite of petrophysical data. This was marked by low gamma ray, high
resistivity, and low acoustic impedance between a true subsea vertical depth
(TVDss) range of 10,350 - 10,450
ft. The AVO fluid substitution yielded a decrease in the density values of pure
gas (2.3 - 1.6 g/cc), pure oil (2.3 - 1.8 g/cc) while the Poisson pure brine
increased (2.3 to 2.8 g/cc). Result from FORMAT 26 plots yielded a negative
intercept and negative gradient at the top and a positive intercept and
positive gradient at the Base which conforms to Class III AVO anomaly. FORMAT
30 plots yielded a negative intercept and positive gradient at the top and a
positive intercept and negative gradient at the Base which conforms to class IV
AVO anomaly. AVO attribute volume slices decreased in the Poisson ratio (0.96
to - 1.0) indicating that the reservoir contains hydrocarbon. The s-wave
reflectivity and the product of the intercept and gradient further clarified
that there was a Class 3 gas sand in the reservoir and the possibility of a
Class 4 gas sand anomaly in that same reservoir.
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