John Gjelberg¹, Kjell-Owe Häger², Geir Indrevær¹, Ole J. Martinsen³, Roger G. Walker⁴

(1) Norsk Hydro Research Center ASA, Bergen, Norway
(2) Norsk Hydro Angola, Luanda, Angola
(3) Norsk Hydro ASA, Bergen, Norway
(4) Roger Walker Consulting, Calgary

ABSTRACT: Morphology of Neogene Turbidite Channel Systems in Block 34, Offshore Angola

Seismic attribute mapping of the Oligocene and Miocene succession in Block 34, offshore Angola, shows a wide range of channel and lobe morphologies. The area of interest is part of a passive margin basin, strongly influenced by salt tectonics, which also influenced the paleobathymetry and distribution of gravity flow deposits. The channel depositional elements can be, based on morphology, classified in three classes: 1) simple sinuous non-meandering channels, 2) narrow and broad channel belts with single- and multi-storey meander complexes, and 3) narrow and broad sinuous erosional and aggradational channel belts with a complex fill. In addition, submarine fan lobe and slump deposits occur at several locations and at different stratigraphic levels.

Most of the Oligocene reservoirs belong to class 1 and 2, whereas the Miocene channels mainly are of class 3. The architectural difference in reservoir development between the Oligocene and the Miocene channels are basically reflected in the degree of channel sinuosity and ability to develop meander loops, in addition to the erosional capacity of the channels.

The erosional and aggradational channel systems in Block 34 (class 3) are of similar shape and size as some of the extensively cored channels in nearby Block 17. The class 3 channels show three main phases of development: 1) The initial phase, dominated by erosion and by-pass. 2) The middle phase, dominated by a complex of sinuous, nested channels, created by lateral migration and cut-off. 3) The final phase of development is characterized by a solitary high sinuousity channel with well-developed levees.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado