Abstract:
Integrated approach of rock physics and seismic inversion analysis were ultilised in
enhancing lithology and fluid differentiation in “AA” field, offshore Niger Delta. The
data set used for the study includes prestack seismic and a suite of well logs from two
wells. Rock physics concepts were utilised to understand the sand and fluid trend from
background trends. Seismic inversion was ultilised to unravel the elastic responses of the
sand saturated with the fluid and that of non-hydrocarbon bearing. Computation of
reservoir properties from well log data using well-established equations was also
executed. Two horizons were identified and mapped from seismic sections using seismic
attributes such as amplitude and reflection geometry. The petrophysical parameters of the
two reservoirs (RES-1 and RES-2) were also estimated to evaluate the quality of
reservoirs. RES-1 has average volume of shale of 15%, effective porosity 29% and
permeability of 755 mD while RES-2 has average volume of shale of 23%, effective
porosity of 24% and permeability 589 mD. Rock physics diagnostics was carried out for
quantitative analysis of lithologies and fluids. The crossplots analyzed classify the study
area into hydrocarbon sands, brine and shale based on large separation between the gas
sand and background trend. Simultaneous inversion revealed that the elastic parameters at
the zone of interest are low compare to the surrounding rocks indicating low
compressional wave velocity, low shear wave velocity, low density and low impedances
in the two reservoirs. These responses showed that the reservoirs are gas saturated.
Integration of rock physics and seismic inversion has added another dimension in the
differentiation of lithologies and different fluids within the hydrocarbon bearing sands
and also helped in characterizing the study field.
