Geochemical Analysis of Albian-Maastrichtian Formations in the Offshore Basin of the Abidjan Margin: Rock-Eval Pyrolysis Study

The Albian-Maastrichtian interval of the Ivorian sedimentary basin has been the subject of numerous sedimentological, biostratigraphic, and geophysical studies. However, its geochemical characteristics remain relatively unexplored. This study aims to determine the oil potential and the nature of the organic matter it contains. It focuses on the geochemical analysis (physicochemical method) of two oil wells located in the offshore sedimentary basin of Côte d’Ivoire, specifically in the Abidjan margin. A total of 154 cuttings samples from wells TMH-1X and TMH-2X were analyzed to determine their oil potential and the nature of the organic matter (OM) they contain. The analyses were performed using Rock-Eval pyrolysis, a method that characterizes the amount of hydrocarbons generated by the organic matter present in the rocks. The key parameters measured include Total Organic Carbon (TOC), Hydrogen Index (HI), oil potential (S2), and maximum pyrolysis temperature (Tmax). These parameters are used to assess the amount of organic matter, its thermal maturity, and its potential to generate hydrocarbons in the studied wells. The results show significant variations between different stratigraphic levels. In well TMH-1X, the Cenomanian and Campanian intervals stand out with very good quantities of organic matter (OM) with good oil potential, although often immature. In contrast, other stages such as the Albian and Turonian contain organic matter in moderate to low quantities, often immature and of continental type, which limits their capacity to generate hydrocarbons. In well TMH-2X, a similar trend is observed. Despite an abundance of organic matter, the oil potential remains low in most of the studied stages. The organic matter is primarily of type III (continental origin) and thermally immature, indicating a low potential for hydrocarbon generation. The study reveals that, although some intervals exhibit high-quality organic matter, the majority of the samples show insufficient maturity for effective hydrocarbon production. Wells TMH-1X and TMH-2X offer limited oil potential, requiring more advanced maturation conditions to fully exploit the hydrocarbon resources.

Geological Interpretation and Identification of Albian-Aged Petroleum Prospects in Block A, San Pedro Margin (Côte d’Ivoire)

The study aims to identify Albian-age oil prospects in Block A of the San Pedro margin, Côte d’Ivoire, by conducting a detailed geological interpretation. The objective is to confirm the presence of oil reservoirs trapped by favorable geological structures, identifiable through geophysical and seismic methods. The methodological approach is based on a combined analysis of studies and seismic data. Drilling data from well PA, including well logs and end-of-well reports, were used to characterize the lithological formations encountered, particularly those of the Albian. 3D seismic profiles were interpreted to identify structures conducive to hydrocarbon accumulation. Isochrone, isovelocity, and isobath maps were developed to refine the interpretation. Sedimentological analyses revealed five sandy/gritty levels between 2610 m and 3100 m, interspersed with clay, limestone, and siltstone beds. The seismic profiles highlighted two main prospects. These prospects exhibit favorable geological structures, including normal faults and structural traps that provide oil traps.

Sequential Analysis in the Identification of 3rd Order System Tract in the Abidjan Margin

The use of sequential stratigraphy concept, based on well logs, sedimentology, and biostratigraphy, has shed light on the complex mechanisms controlling sedimentary accumulations. Consequently, identifying these mechanisms allows us to predict the hydrocarbon generation potential of source rocks. In the Ivorian offshore sedimentary basin, certain studies have contributed to understanding and characterizing the petroleum system. However, these previous works did not integrate biostratigraphic data to highlight sedimentary facies. This study, conducted on two wells in the Abidjan margin, is crucial as it helps us comprehend the geometry of fossil sediments in relation to sea level variations. It will also aid in reconstructing the basin-filling history and predicting the distribution of rocks capable of trapping oil, determining lowstand systems tracts (reservoir rocks), transgressive systems tracts, and highstand systems tracts (cap rocks). Lithological analysis revealed predominantly clayey sedimentation with sandy layers. Well log data facilitated the delineation of formation boundaries and highlighted reservoirs consisting of sands, sandstones, limestones, and occasionally intercalated shales. Integrating these analysis results with biostratigraphic interpretations based on foraminifera and palynomorphs revealed that the traversed formations were deposited in a transitional environment ranging from Coniacian to Maastrichtian ages. Applying sequential stratigraphy concept from well logging resolved dating issues encountered in microfossil-poor or microfossil-free zones. The results of the Coniacian-Maastrichtian age sequential subdivision were aligned with the chart.

Abundance and Source Identification of Polycyclic Aromatic Hydrocarbons in Sediments of the Ivory Coastal Zone (Toukouzou Hozalem-Assinie)

Polycyclic aromatic hydrocarbons (PAHs) are strongly associated with agricultural, residential, transportation, industrial and petroleum activities. In this study, the presence of PAHs (polycyclic aromatic hydrocarbons) was investigated in sediments of the ivory coastal zone (Toukouzou Hozalem-Assinie). The main objectives of this study were to determine the abundance and to predict the source of PAHs in the sediments. Gas chromatography-mass spectrometry (GC-MS) was used to analyze sixteen priority PAHs. Total PAHs concentrations were from 1.31 to 3992.68 mg/kg in sediment with an average concentration of (307.54 ± 16.10) mg/kg. Among all PAHs, Naphthalene (Nap = 332.72 mg/kg) and Phenanthrene (Phe = 41.75 mg/kg) were found in the highest concentration, whereas Benzo (k) Fluoranthene was found in the least concentration in the range of 0 - 0.85 mg/kg (mean 0.24 mg/kg). Bassam-Modeste Lagune (BML) sampling site was the site with the highest concentration of total PAHs (all 16 PAHs) compared to the others due to their location in a highly populated estuary area that receives commercial, tourism, port, petroleum and heavy industrial activities. Diagnostic ratios were used to determine the sources of PAHs and suggested that the PAH profile in the sediments was dominated by 2 and 3 ring PAHs. The patterns of PAH compounds in sediment indicated that contamination is from mixed sources, with a strong indication of petrogenic contamination potentially from spills of fuel, oil and industrial activities.

A Probable Connection between a Bitumen Sample from the Western Niger Delta and Isan Well Sample from the Lower Cretaceous (Neocomian) Shale

An earlier study of GC-MS analysis on bitumen samples from the Agbabu area in Western Niger Delta showed the significant presence of gammacerane and no Oleanane and is suggested to be generated from the Lower Cretaceous (Neocomian) source rock, however, twelve core samples were obtained from the geological survey of Nigeria for both optical geochemical and biomarker analysis, two of the samples from Isan-9 well indicated the presence of Botryococcus braunii a freshwater alga which is characteristic of a lacustrine lake type environment. The extracts from the same core showed m/z = 191 chromatogram with the significant presence of gammacerane which is diagnostic for stratified water columns and characterizes a typical lake environment. However, the m/z = 191 chromatogram also shows the presence of Oleanane which is diagnostic for vascular plant materials, this doesn’t corroborate with that of the Ise-2 well. The Isan-9 well source rock is suggested to have occurred due to the evolving structural geology of the continental shelf after the onset of the rifting, whereby the dominant lake-type environment in the Early Cretaceous was accompanied by a sediment fill of continental runoffs containing vascular plant materials. This implies that an ancient lacustrine lake system was gradually modified as a result of sedimentary infill. And that the bitumen is sourced from the lower Cretaceous Neocomian source rocks.