--> --> Source to Reservoir Correlation and Hydrocarbon Compositions of Oil Sand Deposits in Dahomey Basin, Nigeria

2018 AAPG International Conference and Exhibition

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Source to Reservoir Correlation and Hydrocarbon Compositions of Oil Sand Deposits in Dahomey Basin, Nigeria

Abstract

Oil sands, also known as tar sands, are classified as unconventional hydrocarbon plays and are being exploited to augment global energy needs. Nigeria has the largest conventional oil industry in Africa but is also endowed with marked oil sand deposits. These are found within the Afowo Formation in the Eastern Dahomey Basin. The deposits occur across an area of approximately 120 by 6 km, and the reserves are estimated at about 30-40 billion barrels. Over the last decades, the Nigerian government and oil companies have focused on the exploitation of conventional hydrocarbon reserves with very limited attention to the vast oil sand resources. The current push and paradigm shift to diversify the economy and to increase petroleum reserves and create jobs makes the exploitation of oil sands an ideal target of high national interest. In this study, results from some of these oil sands are presented. Outcrop samples of the source rock, oil sand and bitumen seepage from a location (J4) in the state of Ogun, South Western Nigeria have been evaluated for organic matter maturity and hydrocarbon compositions. Pyrolysis results for the source rock indicate that total organic carbon (TOC) ranges from 5.95 weight % to 18.46 weight % with organic maturation temperature (Tmax) within the range of 417°C to 426°C. A complementary Gas Chromatography (GC) analysis of the free hydrocarbons present within the source rocks illustrates that both light and heavy hydrocarbon components are present. In contrast, oil sand and bitumen hydrocarbon analyses show that mostly heavy hydrocarbon end are present with hydrocarbon chains C6-C12 missing, consistent with biodegraded oils. Such a hypothesis is supported by the high oxygen index of the source rock (oxidation effect). This study demonstrates that these oil sands represent viable exploration targets for the petroleum industry. With vast oil sand deposits in the Dahomey Basin, the exploration and exploitation of this resource will open new frontiers to complement Nigeria’s hydrocarbon production from conventional plays.