Discussion on Controlling Factors of Excellent Marine Source Rocks in Senegal Basin, West Africa

The breaking through of oil-gas exploration have been successively achieved in the recent three years in the deep water area of Senegal Basin, locating in the northern segment of West Africa coastline. It has been proved that the oil and gas came from Cenomanian-Turonian marine source rocks. In order to discuss the controlling factors of this excellent marine source rocks, the author conducted the geochemical study of source rock samples from typical wells, restored the paleo model of depositional and organic facies development. The study shows that there are two types of organic facies developed Senegal Basin. One is shallow water carbonate platform organic facies on the shelf, characterized by medium to relatively high TOC (TOC<3%) and HI (100~400 mg HC/gTOC), as well as the moderate preservation condition, where the organic materials came from the marine organism terrestrial higher plant. With the input of minerals and oxygen-enriched water currents, the depositional environment is oxidizing, as indicated by the S/C ratio (<0.4). The other is the continental slope to abyssal organic facies, characterized by high TOC (TOC>3%) and HI (up to 900 mg HC/gTOC), as well as the good preservation condition, where the organic materials came from the abundant marine organism. The depositional environment is anoxic, as indicated by the S/C ratio (>0.4) and the presence of aryl isoprenoid compounds. It is concluded that the anoxic environment is the controlling factor to the excellent marine source rock in Senegal Basin. Meanwhile, the paleo marine productivity in Cenomanian-Turonian period was higher than that of Jurassic, it also benefited the enrichment of organic materials.