Abstract:
Amplitude variation with offset analysis of some bright spots mapped within the stacked seismic
volume of “T-Rex Field” located within the offshore flank of the Niger Delta Basin has been
considered in this research work. The objective is to discriminate true bright spots, associable with
hydrocarbon saturation, from false bright spots, associable with lithology changes and brine
saturated sands. The examination and quantitative evaluation of the pre-stack amplitude behaviors
with varying source – receiver offset within common mid-point gathers at “bright spots” mapped
within the stacked seismic volume of “T-Rex Field” allowed the delineation and classification of
some hydrocarbon sands on an intercept, 𝐴 versus gradient, 𝐵 crossplot. The results delineated
four hydrocarbon reservoir types in the study field. The dominant hydrocarbon reservoir type is
the Class IV which has a peculiar property of appearing as “dim spots” on stacked seismic data,
hence difficult to resolve. The results from analysing the study field data have proved the
adaptability of offset dependent reflectivity analysis for reservoir pore fluids identification prior
to drilling and wireline log data. The concept of assuming bright spots on stacked seismic records
as drillable targets is valid but with a higher risk of drilling dry holes than when prospects are
analysed in search for positive offset dependent reflectivity signatures. Detailed subsurface
geology and stratigraphy are better inferred from drilling, cores, and wireline logs.
