Using 2D seismic data and well logs from the Kribi-Campo subbasin in the south Cameroon margin, we have analyzed the postrift succession with the aim of deriving a chronostratigraphic chart and identifying stratigraphic traps. The Kribi-Campo subbasin related to the rifting between Africa and South America could be divided into a structurally complex eastern depocenter and a relatively less disturbed western depocenter in which a break-up unconformity approximately 107.5 Ma underlined the beginning of postrift history. We have used the modern concepts of sequence stratigraphy to identify and characterize seven second-order (SS1, SS2, SS3, SS4, SS5, SS6, and SS7) sequences and one third-order (SS8) sequences grouped into three megasequences (A, B, and C) from Albian to Recent. Sequence 1 (Albian-Cenomanian) was characterized by a retrogradation overlying a lowstand progradational pattern. The SS2 (Campanian-Maastrichtian) and SS3 (Maastrichtian) sequences were deposited during a highstand normal regression. From Paleocene to Eocene, the deposition of sequences SS4–SS5 was controlled by the development of submarine fan turbiditic system related to a forced regression of coastline. From the Middle Miocene to Recent age, the SS6, SS7, and SS8 sequences have been characterized by the development of sigmoidal-oblique clinoforms of a deltaic system well observed in the northern part of the study area. We have studied a new undocumented phase of forced regression of Mio-Pliocene in age within the postrift sequence SS7. The forced regression phases are associated with the Paleogene and Neogene uplift. Relative sea-level curves were constructed and compared with the existing published curves. The processes involved in the formation of these sequences were interpreted as a combination of tectonics, sediment supply, and sea-level changes. Potential reservoirs embedded within the sequences include channel fill, shingled turbidites, slope fan, and basin-floor fan complex.

Missole facies description and sequence stratigraphy analysis allow a new proposal of depositional environments of the Douala sub-basin eastern part. The sediments of Missole outcrops (N'kapa Formation) correspond to fluvial/tidal channel to shallow shelf deposits with in some place embayment deposits within a warm and semi-arid climate. Integrated sedimentologic, palynologic and mineralogical data document a comprehensive sequence stratigraphy of this part of the Douala sub-basin. Five facies associations occur: (1) facies association I is characterized by Floodplain deposits; (2) facies association II is Fluvial to mouth bar deposits; (3) facies association III characterise Shallow Shelf deposits; (4) facies association IV represents Distal bay or Lacustrine déposits; and (5) Facies association V is made of Fluvial channel deposits. Six depositional sequences were identified. These sequences are composed of four progradational sequences and two retrogradational sequences containing a fluvial channel portion represented by lag deposits at the base of retrogradational sequences. These deposits represent the outset of the relative sea level rise period. In the study area, the N'kapa Formation is composed of non-marine/coastal aggradational deposits representing the early stage of the regressive period. The occurrence of the estuarine/bay deposits with paleosols development is interpreted as evidence of climate change with significant relative base level fluctuation. The study of key minerals associated to sequence stratigraphy as well as palynology demonstrated that sequence architecture has been controlled mostly by climate evolution and outcrops are dated Paleocene -early Eocene.

L’histoire de la subsidence et de l’évolution thermique du sous-tasse de Kribi-Campo situé dans le Golfe de Guinée ont été contraintes à l’aide de dix puits offshore en utilisant la technique de délestage après décompaction. Quatre principales phases de subsidence ont été discriminées : la première, du Barrémien à l’Aptien (130-112 Ma); la deuxième, de l’Albien au Sénonien (112-65 Ma), la troisième, s'étendant du Paléocène au Miocène (65-5 Ma), et la quatrième du Pliocène au Pléistocène (5-2 Ma). Les cartes de quantité et de vitesse de subsidence et de sédimentation montrent une grande zone subsidente dans la partie ouest du bassin autour de Kribi. Le facteur d’extension β pour le modèle d’extension uniforme correspond à des valeurs allant de 1,04 à 1,06. Graphiquement, les courbes de subsidence tectonique apparaissent encadrées par les courbes correspondant à β =1,03 et β =1,09. Les pentes des courbes linéaires de la subsidence tectonique par rapport à la racine carrée du temps t, ont permis d’avoir des paléotempératures des sédiments ainsi que des gradients géothermiques en parfait accord avec les valeurs observées dans les puits. Par exemple, un gradient de température de 35, 316 OC/km a été calculé avec les températures maximales tandis que celui obtenu à partir des puits est de 35,554 OC/km. La comparaison des valeurs calculées de la réflectance de la vitrinite Ro avec les valeurs mesurées montre une bonne correspondance. Ces valeurs de la vitrinite indiquent que les roches-mères d’âge Crétacé et Tertiaire inférieur ont probablement atteint la maturité thermique.

No abstract

The P10 well is located offshore, in the Northern part of the Rio Del Rey basin in southwest Cameroon. Although the Rio Del Rey basin is the most prolific coastal basin in Cameroon given the production results from several fields in the southern part, yet it remains very little explored in its northern part. This work evaluation the petroleum potential in the northern part of the Basin using a combination of the "Quick Look" interpretation of the logs recorded in well P10 and "complex matrix" facies analysis of the different lithofacies through the neutron porosity - bulk density (NPHI-RHOB) and delta time sonic - bulk density (DT-RHOB) diagrams. The composite log includes the Gamma Ray log; Caliper log; Deep Resistivity log; neutron porosity log and bulk density log. In addition to this composite log, a geological end of well report is completed to refine the results. Ten (10) near sand/sandstone reservoirs were delineated between 950 and 1803 TVD m (true vertical depth in meter) with very good porosities (12% <Φ< 30%) as well as a mineralogical composition dominated by quartz. Clay volumes are relatively lower than 18% except in reservoirs R5 and R6 where they are around 24%, giving the latter a sandy-clay lithology. Reservoirs R2 and R4 contain oil, the latter with a WOC (Water Oil Contact) at ~1172 m and a GOC (Gas Oil Contact) at 1169 m. Reservoirs R6; R7; R8; R9; R10 all contain Gas and Water with WGC (Water Gas Contact) located at ~1431 m; 1530 m; 1690 m and ~1790 m respectively. In the light of these results, there is a clear dominance of gaseous hydrocarbon reservoirs over oil-impregnated ones in the study area. The results provided by this work can serve as baseline data for future oil and gas exploration projects in the northern part of the Rio Del Ray Basin.