Application Of Enhanced Seismic Semblance Attribute To The Characterisation Of Elements Of Deepwater Upper Slope Channels, Offshore Western Niger Delta

Abstract

Deepwater depositional elements are the building blocks of submarine systems and represent the basic mappable elements in seismic volumes. This study utilizes good quality 3-D seismic data of 300 km² areal coverage in water depth of 500 m to characterise the planform morphology and distribution of channel elements in the upper slope of deepwater western, Niger Delta. The seismic interval of interest (between 500 and 1650 milliseconds two-way time (TWT), informally termed ‘Channel System’, was subdivided into six (6) seismic units - Intra Channels (IC) 1, 2, 3, 4, top channel system (TCS), and undeformed hemipelagites (UH). Seismic interpretation was carried out for each of the seven horizons to derive their respective subsurface TWT maps. The median surface between two successive maps were derived to capture their internal architecture within the seismic units based on reconditioning the seismic volume semblance attribute. The resulting semblance attribute maps, from the Intra Channel 1 (IC1) unit through the overlying units to the Undeformed Hemipelagites (UH) unit presented an enhanced planform morphology of various NE-SW trend channels. The IC1 is imprinted with three channels of varying sinuosity, IC2 is characterised by one non-sinuous channel and one sinuous channel, IC3 indicates three non-sinuous channel, and one sinuous channel, IC4 and the TCS’ are both characterised by several sub-parallel channels and one sinuous channel, while the topmost UH unit displayed several straight slope gullies upslope with imprint of one precursor sinuous channel. The identified channel forms vary in morphology, sinuosity and distribution both spatially and across the stratigraphic succession in the upper slope. The progressive temporal disappearance of the channels is linked to the associated background hemipelagites that acted as blankets over the precursor channels.