The Songo Songo and Mnazi Bay gas discoveries indicate the effectiveness of Lower Cretaceous and Oligocene shallow marine and deltaic sandstones as reservoir formations.  In addition Paleogene oil and gas shows in the coastal zone wells point to potential reservoirs in Layer 4 in the MDOB.  Although not hydrocarbon-bearing, outer shelf facies turbidite sandstones of Paleogene and Upper Cretaceous ages with porosities of up to 28% have been observed in some wells.

In the MDOB primary reservoir targets are anticipated to be Miocene to Paleocene (and perhaps Upper Cretaceous) slope and basin facies channel-fill at these stratigraphic levels are likely to be sand prone, having been fed from large volumes of deltaic sand sourced from the Rufiji and Ruvuma paleo-river systems. It should be noted that similar facies of Miocene age are prolific reservoirs in West Africa.
 

The Paleogene and Neogene section is interpreted to comprise several basin-fill megasequences showing shifting depocentres with time. the distribution of sand-prone channels within the sequences can be determined directly from the seismic data by a study of amplitude variations at the target horizons. Illustrated here, for part of the area, is the channel distribution within the basal layer of the Lower Miocene sequence based on RMS amplitude; note the general west-east orientation consistent with a down-slope sediment transport.
 

Other potential reservoirs include the deeper offshore equivalents of Lower Cretaceous shallow marine sandstones, Middle Jurasssic limestones and sandstones of Karroo formations. the depth of burial of these older formations probably precludes their effectiveness as reservoirs, except where their porosity has been preserved or otherwise enhanced; for example, in zones of uplift associated with fracture zones

Seals
The sedimentary sequence in the MDOB is interpreted, in common with other passive margin basins, to be dominantly shale- and mudstone-prone. For the principal reservoir targets sufficient thickness of sealing formations are therefore expected to be present.

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