Benin and Western Nigeria Offshore Basins: A Stratigraphic Nomenclature Comparison

The Benin and Western Nigeria Offshore Basins, which are parts of an extensive basin called the Dahomey (Benin) Embayment, were formed during the Early Cretaceous under similar tectonic conditions and continental sedimentary environments. Based mainly on available lithological, biostratigraphic and paleoenvironmental data, this paper summarizes the stratigraphic succession of theses basins and attempts a comparison of these stratigraphic nomenclatures. The bulk of data shows that sedimentation begins with terrestrial at the base, passes through shallow marine, deep marine (with restrictive bottom circulation) and ends with open deep marine conditions. The stratigraphy of the Offshore Benin Basin was established later and considering lithological and paleontological similarities with formations of various southern Nigeria basins, the stratigraphic chart adopted for this basin was a mixed variant of various Southern Nigerian basins nomenclatures. For the first time, a correlation of stratigraphic charts of each basins and a schematic cross section showing their lithostratigraphic units, especially the Cretaceous-Paleocene interval which is petroliferous, are proposed. The study shows that the nomenclature adopted in Benin Republic must be revised by using type section/locality names for some particular Formations and widely accepted Formations names of Nigeria for the others. This will permit to avoid confusions as it is presently the case for the name “Afowo Formation” representing a Cretaceous sequence in Nigeria and which is use in Benin Republic to distinguish some sediments of Miocene age. Moreover, a High Resolution Biostratigraphy summary (including micropaleontology, nannopaleontology and palynology distributions) relating to each offshore basin is needed for sequences correlations and entire harmonization of the stratigraphic nomenclature of these offshore basins.

Geochemistry of Cretaceous Sea Rocks from the LEO-3X Well in the Eastern Abidjan Margin, Côte d’Ivoire Offshore Basin

In this study, we apply geochemical and statistical analyses to evaluate the source rocks and kerogen type of Cretaceous sediments from the Cote d’Ivoire sedimentary basin. The geochemical analysis includes pyrolysis data such as total organic carbon (TOC%), generation source potential (S2) and hydrogen index (HI). The results of the cluster analysis separated the source rocks in the study area into two main groups. 1) Source rocks characterized by HI > 300 (mg/g), TOC from 1.76% to 3.19% by weight, and S2 from 6.55 to 14.46 (mg/g), indicating good to excellent source rocks with type II kerogen and are capable of generating oil. 2) Source rocks characterized by HI between 200 and 300 (mg/g), TOC from 1.6 to 2.02 wt%, and S2 from 3.45 to 5.36 (mg/g) indicating medium to good source rocks with type II-III kerogen and capable of generating a mixture of oil and gas.

Chemostratigraphic Characterization Tests on Sedimentary Formations in the Côte D’Ivoire Offshore Basin: Case of A-X and B-X Wells

The tests performed with two hundred and thirty-nine (239) samples from the A-X and B-X drillings help to know their sedimentological and chemostratigraphic characters. In sedimentological term formations are composed of sand, sandstone, limestone, siltstone and argillite that alternate along the drill. In chemostratigraphic term two megasequences (MS1 and MS2) have been identified. A correlation of chemostratigraphic data completed by the lithology results allowed a subdivision of oil wells that shows two main types of deposits environments. First, a proximal marine environment to continental and to Albian marked by a detrital flow deducted from the concentrations evolution of indicator elements of terrigenous material that are K, Mg, and Rb. On the other hand, a deep to shallow marine environment of Cenomanian to Paleocene marked by the presence of predominantly clay sediments and abundant glauconite in the lower Senonian. Nevertheless, there is a transition or intermediate environment that is characterized by the presence of glauconite and detrital flows.

Exploration prospects of oil and gas in the Northwestern part of the Offshore Indus Basin, Pakistan

Oil and gas resources are short in Pakistan and no commercially viable oil and gas sources have been yet discovered in its offshore areas up to now.In this study,the onshore-offshore stratigraphic correlation and seismic data interpretation were conducted to determine the oil and gas resource potential in the Offshore Indus Basin,Pakistan.Based on the comprehensive analysis of the results and previous data,it is considered that the Cretaceous may widely exist and three sets of source rocks may be developed in the Offshore Indus Basin.The presence of Miocene mudstones has been proven by drilling to be high-quality source rocks,while the Cretaceous and Paleocene–Eocene mudstones are potential source rocks.Tectonic-lithologic traps are developed in the northwestern part of the basin affected by the strike-slip faults along Murray Ridge.Furthermore,the Cretaceous and Paleocene–Eocene source rocks are thick and are slightly affected by volcanic activities.Therefore,it can be inferred that the northwestern part of Offshore Indus Basin enjoys good prospects of oil and gas resources.

NUMERICAL AND EXPERIMENTAL RESEARCH ON CURRENT GENERATION IN DEEPWATER OFFSHORE BASIN

During the design and construction of the deepwater offshore basin, its current generation system is considered to be one of the key technologies. In this article, the state-of-the-art deepwater offshore basin at Shanghai Jiaotong University was examined as a case study. Different 3-D numerical models of the current generation system were developed and calculated. The uniformity of flow field in the basin, such as horizontal and vertical current velocity profiles, were calculated in detail. Besides, a 1 ： 10 scaled model test was also carried out. The current velocities at different locations in the basin were measured and compared with the calculated results. It is concluded that satisfactory agreement can be resulted between the numerical simulation and model test. In addition, it is suggested that transition sections and turning vanes need to be set in inflow and outflow culverts to improve the uniformity of flow field in the basin. And the hydraulic performance of the deepwater current generation system can meet the requirements of model tests in deep water.