Source rock depositional processes in different marine settings: examples from North African basins

The current thesis assesses source rock characteristics in various shallow marine settings using samples from the Nile Delta and Abu Gharadig basins in Egypt and the Tarfaya Basin in Morocco. The methods include organic and inorganic geochemistry, organic petrology, basin modeling, and palynology. The thesis comprises three main studies. First, the Nile Delta Basin source rock potential is determined using organic geochemistry and petrology as well as 1D basin modeling of two onshore wells. The Abu Hammad-1 well located in the southeastern Nile Delta Basin hosts fair to good gas prone source rocks within the Upper Jurassic and Lower Cretaceous section. The molecular geochemical analyses indicate shallow marine depositional environment and mixed marine and terrestrial organic matter. The burial and thermal numerical 1D model and organic petrology results indicate thermally immature section. However, this Mesozoic section is expected to have better potential and thermal maturity toward the northern parts of the basin. The middle Miocene to Pleistocene section is examined in the Matariya-1 well which is located in northeastern onshore Nile Delta Basin. It contains fair gas prone source rocks in a middle Miocene lowstand wedge. This section has attained onset oil generation stage. The great thickness of the section and proximity to the reservoir facies upraise its source rock potential. The study recommends further exploration in deep targets such as Mesozoic sections, especially in the offshore areas. The second part of the thesis evaluates the source rock potential and paleoenvironment of the Cenomanian to Santonian succession of the Bahariya and Abu Roash formations at the GPT-3 well, Western Desert, Egypt. The study employed organic and inorganic geochemical and palynological techniques. The results show that the succession represents variable oxic shelf depositional environments with low organic matter preservation excluding the Abu Roash “F” Member which shows two source rock facies. The basal part of this member is rich in carbonate, TOC and marine organic matter. The kerogen is relatively rich in organic sulfur (Sorg) due to the limited reactive Fe supply upon deposition leading to excesses S incorporation into organic matter. The middle part of the Abu Roash “F” Member is lean in organics and very rich in terrestrial elements (e.g. Fe, Ti, Si) and associated with Botryococcus indicating sea regression. This facies overlain by a suboxic marine oil prone source rock with lower Sorg contents. Both source rocks are lower in Tmax as compared to the above and below sections implying thermal maturity retardation possibly due to high liptinite contents, high pressures or lack of catalytic elements. Moreover, two oil reservoirs were geochemically characterized. These findings are vital for future hydrocarbon exploration and paleoenvironment reconstructions. In the Tarfaya Basin, Cenomanian to Turonian source rocks are classified based on their organic geochemical and petrological properties. The molecular geochemistry suggests marine anoxic depositional environment with an extreme oxygen depletion attained at the Cenomanian/Turonian boundary event (CTBE) associated with increased cyanobacteria activities. The lower Cenomanian is characterized by higher silicate contents compared to the rest of the section based on major elemental data. All samples are dominated by submicroscopic organic matter. The lower Cenomanian is poor in bituminite, whereas, the upper Cenomanian to Turonian samples show variable bituminite contents. Furthermore, the samples show variable Sorg contents. The change in organic matter type was controlled by early diagenetic kerogen sulfurization, which depends on the interplay between S, Fe and organic matter, and upwelling processes. The source rocks are classified into 1) low Sorg and moderately TOC-rich oil prone source rocks (lower Cenomanian), 2) moderate Sorg and TOC-rich oil prone source rocks (upper Cenomanian), 3) high Sorg and TOC-rich oil prone source rocks (Turonian) and 4) very high Sorg and TOC-rich oil prone source rocks (CTBE). Types 2 to 4 will generate sulfur-rich petroleum upon maturation or artificial oil shale retorting