SEISMIC ATTRIBUTES AND AVO FOR RESERVOIR IDENTIFICATION, NAYIL RESERVOIR, SUTTAIB FIELDS, MUGLAD BASIN, SUDAN

Abstract

The study area is located in Muglad Basin, Sudan, and is situated in the western trend of Block 4, GNPOC concession area. The target reservoir Nayil_B sand was deposited in the fluvial-floodplain and lacustrine environments, and is characterized by thin sand interbedded with thick shale of Nayil Formation. The conventional seismic data, due to the thickness of the sand, cannot image the reservoir distribution. Uses of AVO/inversion and seismic attributes have improved the mapping of the reservoir in the study area. The workflow began with rock physics feasibility analysis that indicates the P-impedance parameter as a single parameter that cannot identify any sand from shale. Then, by cross-plotting two parameters it helps to separate sand from shale by using VP/VS ratio, Density against P-impedance and sometimes V-clay. Results from the rock physics indicate that both fields (Suttaib, Suttaib South) have different parameters to discriminate the sand from shale for the same reservoir Nayil_B. The best parameter in Suttaib South is VP/VS ratio, whereas in Suttaib Field it is the density. The low frequency model created for the P-impedance, density and VP/VS ratio, and then the simultaneous inversion was executed to compute the same parameters. Two types of seismic attributes were generated for volume and surface attributes. The attributes show good results for structural features and support the inversion results. The current study concludes that the simultaneous inversion and seismic attributes can image the sand distribution of the Nayil_B reservoir. The results explain the reason for the dry wells that were drilled only based on structural trap not based on sand distribution as shown by the simultaneous inversion and seismic attributes.