Aromatic Compositions of Different Occurrence States in Deep Carbonate Rocks from Tarim Basin

Key words: 
• Tarim Basin

Abstract: Aromatic compositions and thermal maturity parameters of free organic matter (chloroform bitumen A) and inclusion organic matter (chloroform bitumen C) in deep carbonate rocks (>5 700 m) from Well Tacan 1 were studied. The relative distributions of phenanthrenes and dibenthiophenes are richer in the aromatic hydrocarbons of deep carbonate rocks, in the meantime, the abundance of phenanthrenes and chrysenes abundance increase with buried depth, but the dibenthiophenes, naphthobenzothiophenes and fluorenes abundance in aromatic hydrocarbons showed reverse trends, this probably reflect the different thermal stability of various aromatic hydrocarbons at high and overmature stages. There are obvious differences in aromatic compositions and maturity parameters between two occurrence states of deep carbonate rocks, comparing with free organic matter, the maturity of the inclusion organic matter are lower and retarded in the same source rock. There are some aromatic maturity parameters can still be used to assess maturity during overmatre stages, including alkylation ratios of phenanthrenes (C1P /C4P, C1P /C3P, C2P /C4P, C2P /C3P), and maturity parameters for dibenthiophene (MDR, C1/C3DBT,2,4/1,4DMDBT and 4,6/1,4DMDBT). Although DBT/P are thought to an indicator for organic facies, it is showen from this study that this parameter is related to maturation level, which is a good maturity parameter at the same organic facies in high and over maturity stage.