Oil & Gas Geology ›› 2006, Vol. 27 ›› Issue (3): 340-347.doi: 10.11743/ogg20060308

Previous Articles     Next Articles

Geochemical behaviors and origin of reservoir bitumen in Puguang gas pool

Cai Xunyu1, Zhu Yangming2, Huang Renchun1   

  1. 1. Research Institute of Southern Exploration and Development Division Company, SINOPEC, Kunming, Yunnan 650200;
    2. Department of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang 310027
  • Received:2006-04-27 Online:2006-06-25 Published:2012-01-16

Abstract:

Systematic geochemical analyses show that the reservoir bitumen in Feixianguan and Changxing Formations in Puguang gas pool are residuals of the original oil in fossil oil pools after they have been thermally cracked into gas.The organic elementary compositions of the bitumen are characterized by poor hydrogen and rich oxygen and sulfur,suggesting that it is of pyrobitumen as a result of high maturity and TSR.The bitumen has δ13C values ranging from-25.60‰ to-27.78‰ and fits isotopically with kerogen in the Upper Permian source rocks(-26.5‰ to-29.2‰),indicating a genetic relationship between them.The n-alkanes with a complete range of carbon number are observed in the saturated hydrocarbons of the bitumen and no evidences of severe biodegradation occur.They exhibit a phytane predominance with Pr/Ph ratios less than 1.0; predominance of C27 compounds occur in the steranes with detectable C30 and C26 steranes;and the terpanes are characterized by abundant tricyclic terpanes and gammacerane.All these indicate that aquatic organism-dominated marine source rocks have been deposited in a reducing environment.As a result of aromatization of organic matter during the thermal cracking of original bitumen into gas,the aromatic hydrocarbons in the bitumen are characterized by abnormally abundant tetra-and penta-cyclic compounds,and predominated by parent aromatic compounds without alkyl chain,such as fluoranthene,pyrene,chrysene, benzofluoranthene etc.The distribution pattern and MPI index of aromatic hydrocarbons reveal a high thermal evolution for the bitumen with a corresponding Ro value of over 2.0%.

Key words: organic element, carbon isotope, biomarker, aromatic hydrocarbon, bitumen, Puguang gas pool, Sichuan basin

CLC Number: