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

Abstract

Summary 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.