Abstract: Implication Examples of Compound Specific Isotopic Analysis in the Oil and Source-rock Correlation

XU, YONGCHANG, WANG WANCHUN, SHEN PING, Lanzhou Institute of Geology, Chinese Academy of Sciences, Lanzhou 730000, China

1. The oil sand of the Triassic system from Aican — 1 well of the Turpan-Hami basin.

a. The d¹³C values of the hydrocarbon monomers from the abstract of the oil sand are obviously different from that of the oil from coal of the Jurassic system. So it is certain that the source of the oil sand is possibly related to the lacustrine source rock of the Palaeozoic era.

b. The d¹³C values of methane ( — 55. 1), ethane ( —55. 6) and propane ( — 35. 0) of the absorbed gas from the off sand were analysed by the GC—C—MS, the content of methane, ethane and propane in the absorbed gas are 0. 0054%, 0. 0028, 0. 0006% respectively. This absorbed gas was formed by the biodegradation of lacustrine oil.

2. There are two peaks in the gas chromatogram of the hydrocarbons of Shen — 1 well of the Turpan-Hami basin, one is C₆~C₁₈, with d¹³C values from —23.5 to —27. 7, the other is C₂₀~C₂₈, with d¹³C values from —35.8 to —37. 7, it shows the character of mixed sources of oil from coal and oil from lacustrine source rock.

These researches are helpful for the discovering of resources in the Palaeozoic erathem in this basin.

3. The d¹³C values of hydrocarbon monomers of immature and mature oil in the Liaohe basin are different. For immature oil, the d¹³C values of normal alkanes range from — 26. 3 to — 32.5, the d¹³C values of pristane are from —27. 7 to —29. 3 the d¹³C values of phytane are from —29.0 to —30. 7 For mature oil, the d¹³C values of normal alkanes range from — 23.5 to —29.2, the d¹³C values of pristane and phytane are —31. 3 and —30.7, respectively. This shows that the microbial oxidation is stronger in mature oil than in immature oil.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah