Seismic Sequence Stratigraphic Analysis Of The Douala Basin, Cameroon

Abstract

ABSTRACT The Douala Basin is a divergent basin along the West African coast which developed by rifting between Africa and South America during break-up of Gondwanaland. This rifting resulted in the formation of a break-up unconformity near the beginning of Albian time. Biostratigraphic analysis of the Kribi R-1, Kribi N-1 and Campo R-1 wells indicates that the break-up unconformity developed approximately 107.5 million years ago. Although the break-up unconformity developed by tectonic processes, erosion along it was increased by sea-level fall. Wells which penetrate this unconformity exhibit thick sequences of non-marine sands. Production in the Sanaga Sud Field occurs in these strata. Seismic interpretation is mostly in the Late Cretaceous to Pliocene strata. Late Cretaceous strata are relatively thick in the central and northern portion of the Douala Basin and thin near structural highs in the vicinity of the Kribi R-1, Kribi N-1, Kribi B-1 and Campo R-1 wells. Seismic data indicates that strata thicken to the north. The Late Cretaceous sequences identified are the 98.0, 94.0, 90.0, 80.0, 77.5, 75.0, 71.0 and 68.0 Ma boundaries. Deposition occurred in outer neritic water depths over much of the basin including the area near the Kribi R-1 and Campo R-1 wells. The sediments in the onshore Kwa-Kwa 2X and offshore Yassoukou Marine-1 wells are interpreted as slope deposition. This indicates that the basin extended for some distance into onshore Cameroon along an embayment separated from the offshore Niger delta by the Cameroon Volcanic Line. REGIONAL SEQUENCE STRATIGRAPHIC ANALYSIS OF THE DOUALA BASIN, CAMEROON Introduction Despite the presence of major reserves in Calabar Flank and Niger Delta to the north and Gabon Basin to the south, the Douala Basin in offshore and onshore Cameroon (Figure 1) remains woefully underexplored. With the exception of the Kribi and Sanaga Sud fields (both giant gas fields) approximately three offshore exploration wells have been drilled in an area that is larger than the Midland Basin in West Texas. Relatively few wells have been drilled onshore as well. Geochemical analyses by Mr. Marcel Batupe suggest that Cretaceous source recks are similar to those which generated large quantities of oil in both Gabon and Nigeria. He also stated that many medium to large undrilled amplitude anomalies were present in the Douala Basin. In order to demonstrate the hydrocarbon potential of the Douala Basin, the National Hydrocarbons Corporation of Cameroon initiated a pilot project to determine the regional sequence stratigraphic framework of the Douala Basin. The study was designed to address specific exploration problems and to establish a base for future structural and stratigraphic work. Exploration efforts have been slowed by the paucity of sands in many areas of the Douala Basin, especially in the Neogene. Therefore, our work has focused on using biostratigraphic data, seismic and well-logs to help delineate sandy reservoir facies and to determine time intervals most favorable for sand deposition.