Estimation of net-to-gross of among hydrocarbon field using well log and 3D seismic data

Abstract

We present quantitative estimates of net-to-gross of Amangi Field from seismically derived rock properties. We employed well log calibrated seismic inversion attributes using Rock Physics and prestack seismic (AVO) inversion. Crossplots of rock properties and attributes of the well log data from the target reservoirs were analyzed. The reservoir sands were found to have high P-impedances values comparable to the shales (22,000 g/cm 3 ft/s - 28000 g/cm 3 ft/s). Thus, P-impedance alone could not separate the sands from the shales while the S-impedance domain does. The sands are termed hard sands. This is indeed a classical case in the Niger Delta where the normal trend had been the sands having a lower P-impedance than the shales. A trend of increasing N/G was observed in moving from the shale to the reservoir sands and decreasing N/G in moving from the reservoir sands to the sealing shale. To further buttress this findings seismic AVO inversion for Vp/Vs volume and N/G volume and map were obtained from the 3D seismic data. These indicated high N/G values (0.4 - 1.0) and low Vp/Vs values (1.6 - 1.8) for the reservoir sands across the field. The N/G map will be used to select possible locations for development wells. Keywords: H1000 and H4000, inversion, net-to-gross, P-impedance, S- impedance, Vp/Vs ratio,