Petroleum Potential of the Congo Basin - Geology and Resource Potential of the Congo Basin - page 360

Since the JNOC campaign, several reviews of the existing
data have been prepared by Oil Search/Pioneer ( 2007 ) and
HRT Petroleum (Mello 2008 ), in order to evaluate the
hydrocarbon potential of the CB, with the aim of attracting
potential investors and promoting hydrocarbon exploration.
In parallel, hydrocarbon shows (e.g. oil seeps) have been
reported since 2005 along the Lukenie and Tshuapa rivers
and along the shores of the Lake Inongo (lumps of bitumen
on lake beaches). These were sampled and analysed by HRT
Petroleum (Mello 2008 ), who identified them as remains of
black oil generated by prolific and abundant source rocks.
He further suggests that giant oil accumulations could have
been formed:

along the basin margin (Verbeek 1970 ; Lepersonne 1977 ). A
synthetic stratigraphic column was presented by Daly et al.
( 1992 ), assuming long-distance lateral continuity of the
stratigraphic groups. However, this concept appears to be
of limited applicability at basin scale, because the strati-
graphic units vary laterally both in facies and thickness
(Linol 2013 ; see also Linol et al., Chaps. 7 - 9 and 11 , this
Topic). A revised and more detailed stratigraphy is presented
in Kadima et al. ( 2011a ; and Chap. 6 this Topic), taking into
account the spatial distribution of the observations (Fig. 18.2 ).
The development of the CB appears controlled by a series
of tectonic events, defining three first-order tectono-strati-
graphic units that are separated by prominent seismic
reflectors, broadly correlated to the Neoproterozoic,
Palaeozoic-Triassic and Jurassic-Cenozoic. Deposition was
also controlled by variable climatic factors and changing
paleogeographic position of Gondwana/Africa (Scotese
2009 ; Torsvik and Cocks 2011 ). The Gondwana continent,
of which the Congo Shield formed a central place, was
amalgamated at the Neoproterozoic-Palaeozoic transition
(550-530 Ma), in a series of events defining the Pan-African
orogeny (e.g. De Waele et al. 2008 ).
Sedimentation in the CB started in the Neoproterozoic
during a phase of intracratonic rifting (Daly et al. 1992 ). This
initial rift structure is consistent with aeromagnetic and
gravity data (Chorowicz et al. 1990 ; see also Raveloson
et al., Chap. 1 , this Topic) and might be connected laterally
to the Sankuru-Mbuji-Mayi-Lomami-Lovoy failed rift basin
that hosts the Meso- and Neoproterozoic Mbuji-Mayi Super-
group (1155 Ma to ca. 800 Ma; Delpomdor et al. 2013 ; and
Delpomdor et al., Chap. 4 , this Topic). Post-rift subsidence
controlled the deposition of a first sedimentary sequence
during the Cryogenian and the Ediacaran (seismic unit A
of Kadima et al. 2011a ; Delpomdor et al., Chap. 4 , this
Topic). This sequence is part of the type Lindian Supergroup
described by Henry ( 1922-1923 ), Sluys ( 1945 ) and Verbeek
( 1970 ) in the Lindi-Aruwimi region, north of Kisangani
(Fig. 18.1 ). In this Lindian type region, it comprises ~ 130 m
of stromatolitic carbonates at the base (Ituri Group),
followed by ~ 470 m of siliciclastics and limestone
(Lokoma Group) deposited in an environment interpreted
as lagoonal to marine (Verbeek 1970 ). The Ituri Group
contains the Penge arkoses (10-20 m), Lenda carbonates
with carbonaceous layers (80-130 m) and Asoso shales
and sandstones (50 m). The Lokoma Group comprises the
Akwokwo tillites (0-40 m), the Bobwamboli conglomerates
and arkoses (50-250 m), the Mamungi grey shales and
limestones (200-500 m) and the Kole shales (100 m).
In the Lindi-Aruwimi region (Fig. 18.1 ), the Ituri Group
is unconformably overlain by up to 2,000 m thick
siliciclastics (Aruwimi Group: Verbeek 1970 ; Tait et al.
2011 ). This possibly forms the base of seismic unit B of
Kadima et al. ( 2011a ) in the centre of the CB. In outcrop, it is

The integration of all geological, geochemi-
cal and geophysical data available today suggests that the
Cuvette Centrale Basin is an overcharged petroliferous
basin that could be considered, today, one of the last
provinces in Africa to hold giant to supergiant light oil,
condensate and gas accumulations. The presence of oil
seeps widespread around most of the Central Basin
suggested a light oil/ gas prone system. The size of the
structural highs, surpassing more than 1,000 km 2 and,
together with the presence of at least two active oil systems
in most of the Basin, indicate that all elements and processes
of the petroleum systems are active and works in the Basin.

“

”
More recently, the basin structure and source rock poten-
tial have been re-evaluated by reprocessing existing geo-
physical data (Kadima et al. 2011a , b ) and re-analysing
source rock samples stored at the RMCA (Sachse et al.
2012 ). In the light of these recent studies, Comico SPRL
and Centrale Oil and Gas Ltd. asked GhGeochem for an
independent review of existing geochemical data on source
rocks and seeps (Harriman 2011 ) and the RMCA to organise
in 2011 a new seeps sampling campaign to resample those
visited by HRT Petroleum in 2007. The seeps were analysed
by the same GhGeochem laboratory and the results com-
pared and re-interpreted in the light of the previous results of
HRT Petroleum (Harriman 2012 ).

18.3 Tectono-Stratigraphic Evolution

of the Congo Basin

According to Daly et al. ( 1992 ) and Kadima et al. ( 2011a , b),
the evolution of the CB started in the Neoproterozoic
(~700 Ma ago), probably in an intracratonic extensional
context. They suggested that subsequent subsidence during
the Phanerozoic was, at least partly, related to the cooling of
the stretched lithosphere and several episodes of basin
inversion.
The general stratigraphic evolution has been synthesized
by Lepersonne ( 1977 ), Lawrence and Makazu ( 1988 ) and
Daly et al. ( 1992 ), based on the results of exploration
projects, correlating well-logs with field-based observations