AMPLITUDE VARIATION WITH OFFSET ANALYSIS FOR HYDROCARBON PROSPECTING OF “T-REX FIELD”, OFFSHORE NIGER DELTA

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.