Sedimentological Models of the Oligocene and Miocene Malembo Formation in Offshore Angola (Lower Congo Basin)

Francois Temple¹ and Olivier Broucke^2
1 TOTAL, 64018 Pau, France
² TOTAL, 92078 Paris, France

The two sedimentological models presented herein were carried out by integration of well data (cores, logs) and high resolution 3D seismic data (restored and flattened lines to subtract post-depositional deformation).

Deposited in a marine deep-water environment (base of slope to basin environment), the Oligocene Malembo formation is mainly composed by channel-levee complexes. Most of them are characterised by a basal erosional fairway bordered by large external levees. Axis of typical channel-levee (between the two external levee crests) is 2 km-wide and 100 m-thick. Levees widespread over 5 km on both sides of the axis. Wide initial sedimentary bodies (initial levees, terminal or avulsion lobe) were deposited before the development of the channel-levee complex. In the contrary, the Miocene Malembo Formation is mainly composed by both erosive channel complexes (without large external levee ) and ponded lobes, isolated within a hemipelagic background.

Oligocene and Miocene channel deposits determine the limits of a channel belt, which result in a stack of several perfectly fitted channel-levee phases. The last ones seem to be more organized, characterised by increasing in sinuosity and by developing lateral channel migration. In that way, channels and confined levees are the main architectural elements which compose the channel belt. In core data, each channel phase is composed by several characteristic facies associations such as basal channel fill, end of channel fill, channel margin, proximal sandy levee, shaly levee, channel plug.

The sedimentological model directly involves in spatial distribution of reservoir bodies, for exploration phases as well as during field development.