M. Saidi

The Organic Geochemistry of Source Rocks, Bitumens, Asphalts and Oil Stains from Northern Tunisia

The Northern Tunisia (Northern Africa) is a promising area for oil/gas exploration. The organic geochemitry analyses of more that 1000 source rock samples and 100 oil seeps and solid bitumens were performed using GC-MS, IRMS and Rock-Eval pyrolysis techniques. The oil seep samples were collected from the Northern onshore Tunisia, associated with fracture, fault and ftrata in the Mesozoic and Cenozoic reservoirs and seals. Three primary source rocks are studied corresponding to the Albian, Late-Cenomanian-Early Turonain and Ypresian, showing good to excellent oil/gas potential. Three secondary source rock levels of Barremian, Paleocene and Miocene age are also studied and were found to display localy low to fair source rock characteristics. Based on the geochemical data, the oil seeps from the Northeast and Northwest areas were sourced from the three primary source rocks. The Albian and the Late-Cenomanian-Early-Turonain source rocks are the major oil source in the areas. While in South area, the oil seeps was initially charged by the Albian source rock. The Late-Cenomanian-Early-Turonain is the second source rock sourcing several oil seeps. The Barremain source rock only partly contributed in the south area. The oil seeps were found in fractures associated to the NE-SW and NW-SE trending fractures.

Organic Geochemistry of the Ypresian Source Rock and Oil Seeps from Thrust Belt Zones - Northern Tunisia

The thrust belt domain of North Africa is an important hydrocarbon province in the Mediterranean Sea and northern Tunisia. In spite of the long history of exploration in northern Tunisia, little information is available on Ypresian source rock in the thrust belt area. In the presented study the generative potential, depositional environments, thermal maturity and oil seeps of the YpresianBouDabbous organic-rich facies were characterized by both Rock Eval and molecular analyses. The present study indicates that the BouDabbous Formation displays variable source rock potential within the different Tellian units (Kasseb, EdDiss, AinDraham and Adissa units). Organic matter content and petroleum potential are generally poor to fair (up to 1.95% and 6 kg of HC/t of rock respectively) and marine type II kerogen. An increasing maturity gradient from the SE (Kassseb unit) to the NW (Adissa unit) is well documented. Indeed, the BouDabbousfacies are: marginally mature in the front of the nappes (Kasseb unit), mature to late mature within Nefza-Ain Allega tectonic window and overmaturea long the Cap-Serrat-Ghardimaou Master Fault (Adissa unit). In addition, Oil/Oil and Oil/source rock correlations shows a positive genetic correlation between the oil seeps and the BouDabbous source rock.

Migration Pathway Evaluation through Analysis of Hydrocarbon Seeps in the Pelagian basin, Sahel of Tunisia

New macro oil and gas seeps are detect in shallow water on Sousse area (Onshore pelagian, Sahel basin). This area contains significant hydrocarbon accumulations and many potential source rocks. The crude oil and gas seeps have been investigated using biomarker and stable carbon isotope analyses to perform oil-oil and oil-source rock correlations. The gas seep, composed of Methane, Ethane and CO2 appears to be of mixed origin (thermogenic and microbial). The studied oil samples show two distinct sources of hydrocarbon: the first oil seeps (SS-12) appears to be highly mature, showing evidence of chemical and/or biological degradation and was derived from a clay-rich source rock deposited in suboxic conditions. It has been sourced mainly by the lower Fahdene (Albian) source rocks. The second oil seeps (SS-11) was derived from a carbonate-rich source rock deposited in anoxic conditions, well correlated with the Bahloul (Cenomanian-Turonian) source rock. Integration of seismic, Basin Modeling, geological and geochemical analyses provides a means of tracing natural oil seeps and establishing their relationship to fault geometries in the subsurface. The two types of oil seeps and their properties indicate distinct oil characteristics (compartmentalization), multi-periods of migration and accumulation and indicators of tectonic discontinuities.

Oil Ocurence and Migration Pathways in Central and Meridional Atlas of Tunisia

The analysis source rock of the central and meridional Atlas of Tunisia indicates that the Albian Fahdene Fm has a substantial oil-generation potential. The Cenomanian-Turonian Bahloul Fm exhibits fair to high organic content and petroleum potential immature to mature source rock. The Jurassic source rock exhibits fair to good organic content and petroleum potential located in the south of this area. Molecular characterization indicates that most of the produced oils appear to be sourced from a predominantly shaly marine and mature source rock deposited in suboxic to oxic depositional environment. Oil stains located in the northern part of the area seems to be sourced by a marly or argillaceous limestone. Oil-oil correlations and molecular characteristics of selected source rock samples and maturation models suggests that oils were generated from similar source rock and/or organic facies. The Fahdene Fm is the best source candidate to generate these fluid samples. The integration of benzocarbazoles as geochemical molecules tracer has permitted a relative estimation of the lateral migration distance for the different accumulations of the area. Basin modelling outlined the extent of the different petroleum systems in the area and permitted the elimination of the risky prospects for the next exploration phase.