Saturated biomarkers in the estimation of organic geochemical homogeneity of crude oils from four oil fields in Libya

Abstract

Seven crude oils from four oil fields in the Sirte and Murzuq Basins in Libya were investigated in order to estimate their organic geochemical homogeneity. Saturated biomarkers (n-alkanes and isoprenoids) were analyzed using gas chromatography–mass spectrometry (GC–MS). The parameters calculated from the distributions of n-alkanes and isoprenoid aliphatic alkanes, pristane and phytane were used to interpret the organic geochemical characteristics of the oils. Based on the high relative concentration of lower n-alkane homologues in the C11–C16 range and high API values, the oils were classified as light oils. These results also implied that the oils were not biodegraded. The parameters calculated from the distributions of saturated biomarkers indicated that all investigated oils were generated from source rocks containing organic matter of a similar marine origin but with a contribution of terrestrial organic matter. The results also demonstrated that these source rocks were deposited in an oxic environment. The same source rock or the same type of source rocks for all seven samples were postulated. It was concluded that, if the crude oils from these distant basins originated from the same source rocks, they must have had different lengths of their migration pathways.