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The Coastal Basin

The DRC comprises three separate sedimentary basins : the Coastal basin along the west of the country, the Cuvette Central basin which covers part of the interior, and the extension of the East African Rift basin on the eastern margin of the country.

The Coastal Basin was formed by the rifting and separation of the African and South American continents which began 150 million years ago. The rift phase is represented in the sedimentary record principally by lacustrine sediments deposited in continental rifts. Subsequent thermal subsidence allowed marine incursion and the development of extensive evaporite sequences which resulted in thick salt which extends along the African and South American margins. The continued separation of the continents resulted in the post-salt "drift" sequences of marine carbonates, sands, silts and shales.  The oil reservoirs in the DRC are found in both the pre-salt and post-salt units.  

The oil is formed by the transformation of organic matter in the sediments, which then migrates and in favourable circumstances can be trapped in the pores of reservoir rock.  The DRC's crude has low acidity, no sulphur, good viscosity and medium density. It is appreciated by refineries for its diesel content (about 30%) and good general properties.

How much of it can be produced depends on its own internal characteristics, such as its viscosity and density, and on the properties of the reservoir rock (permeability, porosity, heterogeneity). Typically rocks are highly heterogeneous. As a general rule total recovery rates lie between 5% and 40%, and seldom exceed 50%.  Hence, on average more than half the original oil remains unproduced and in some instances more than 90% remains trapped.