An Integration of Genetic Inversion and Seismic Frequency Attributes to Delineate Reservoir Targets in Offshore Northern Orange Basin, South Africa

Abstract

A combination of genetic inversion (Seismic Impedance and Porosity) and seismic attributes (Instantaneous Frequency and Iso-Frequency) are used to characterise Albian and Cenomanian clastic reservoir targets in offshore, northern Orange Basin. The reservoirs are mapped from the well Af-1 position throughout the seismic volume after initial seismic-well tie and consequently, Time-Depth relationship established. Frequency filtering was performed as a form of post stack seismic processing technique to remove passive noise and enhance geological features. Seismic acoustic impedance inversion calibrated with porosity inversion reveals the presence of fluvial channels and associated point bars deposit within meandering channels within the Cenomanian and Albian sequence. The identified channels expectedly show high porosity along its geometry compared to its surrounding lithology. Iso –Frequency (Frequency decomposition) using the Cosine Correlative Transform (CCT) was applied to identify the sweet spots. Iso- frequency of 45 Hz, 12 Hz and 8Hz windows were captured to isolate hydrocarbon charged reservoirs within the Albian and Cenomanian sequence. The CCT method shows that 8Hz window resolved stratigraphic features present within the seismic volume but unable to resolve the presence of hydrocarbon charged reservoirs. However, the application of Instantaneous Frequency (IF) attribute reveals the presence of hydrocarbon charged Cenomanian reservoirs in close proximity to a fault judging by the attenuation of frequency observed. This was achieved by using Thirty –three seismic traces as an input in the Hilbert transform window, subsequently, trace envelope and instantaneous phase were transformed into instantaneous frequency. This study demonstrates the effectiveness of integrating different seismic attributes as a non-invasive approach in characterising clastic reservoirs.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017