HYDROCARBON GENERATION POTENTIAL OF DIFFERENT STRATIGRAPHIC UNITS OF THE CENTRAL CONGO BASIN, DRC

The Central Congo Basin in the Democratic Republic of Congo is one of the largest intracratonic basins worldwide, but poorly investigated with respect to petroleum generation potential. The purpose of this study was to characterize the hydrocarbon generation potential of various stratigraphic units in the Central Congo Basin. Therefore, outcrop and well samples (wells Samba and Dekese) covering various stratigraphic units were sampled, and analyzed using organic geochemical (i.e. GC-MS: biomarker parameters) and petrological (i.e. vitrinite reflectance measurements) methods. The research revealed two highly potential source rocks of Late Jurassic (Stanleyville formation) and Early Cretaceous (Loia formation) age in the north-eastern part of the Congo Basin. Organic carbon content is moderate to high (19 %), with dominating type I kerogen of excellent quality in the Stanleyville Formation and type I/II kerogen in the overlying Loia Formation. Based on biomarker analysis/n-alkane distribution a lacustrine, anoxic depositional environment can be assumed for these units. However, thermal maturity parameters such as biomarker ratios, vitrinite reflectance, T_max and PI values characterized the organic matter of both formations as immature with respect to significant petroleum generation. Finally, vitrinite reflectance data was used to calibrate 1D models for wells Dekese and Samba, which give an overview about burial-, thermal-, and maturity history of the area. The model revealed for well Samba one significant main phase of subsidence which started in the Late Jurassic/Early Cretaceous and shifted the Stanleyville Formation to a depth of approx. 2 km. The base of the Loia Group, for which calibration data is available, reached a depth of ~ 1600 m. Highest temperatures which were calculated for the Stanleyville Formation thus reached approx. 120°C, for Loia Formation approx. 110°C.

Both Stanleyville and Loia Formations can be regarded as excellent petroleum source rocks and could be part of a petroleum system if sufficient burial and maturation has occurred. We conclude that exploration for conventional oil should focus on positions in the basin where the Late Jurassic/Early Cretaceous sequence has reached greater maturity than in case of the areas investigated here.