The study made a quantitative analysis of diamondoid

dibenzothiophenes and thiadiamondoid series in the crude oil from Well Luosi-2 via the GC-MS method with internal standards.The concentrations of diamondoid and 4-+3-methyldiamantane(4-+3-MD)are 10818 and 331 g/g in the study area

suggesting that the crude oil suffered serious cracking and the proportion of cracking oil is up to about 90%.The diamondoid indexes show that the maturity of crude oil from Well Luosi-2 is above 1.6% R

c

.Complete thiaadamantane

thiadiamantane

thiatriamantane series were detected from the Well Luosi-2 crude oil

with the contents of thiadiamondoid

thiaadamantane

thiadiamantane

thiatriamantane being 192

160

26 and 6 μg/g respectively.The high concentration of thiadiamondoid is a sign that the degree of thermochemical sulfate reduction(TSR)of oil from Well Luosi-2 is higher than that of most crude oil from the Lower Ordovician Yingshan Formation in Tazhong uplift.TSR results in the higher DBTs

about 8 201 μg/g

in the oil from Well Luosi-2

and in turn the higher ratios of DBT/P

C

0

-/C

1

-DBT and C

1

-/C

2

-DBT.