The Cambrian carbonate reservoirs of Tazhong uplift is rich in oil and gas.However

there are different opinions on the origin and genetic types of oil and gas in this area due to the complex tectonic setting.In this paper

we studied the origin and genetic types of oil and gas through a detailed analysis of the composition and carbon isotope data of condensate oil and gas in different intervals of the Cambrian in ZS1

ZS1C and ZS5 wells and the geochemical characteristics of the Cambrian-Lower Ordovician and Middle-Upper Ordovician source rocks.The results indicate that the Cambrian gas in the Tazhong uplift is typical cracking gas of sapropelic kerogen.Gas in the Xiaoerbulake Formation is typical over-mature dry gas with a drying coefficient of higher than 0.98 and N

2

content of 2.5%~4.0%.The carbon isotopes of group composition and individual n-alkanes of condensate in the Xiaoerbulake Formation are relatively heavy.The carbon isotope of C

9

-C

20

n-alkane are -28.8‰~-26.3‰.These geochemistry characteristics indicate that the condensate oil and gas in the Xiaoerbulake Formation originated from the Cambrian-Lower Ordovician source rocks.While the natural gas in the Awatage and Wusonggeer Formations is low-mature wet gas with a drying coefficient of 0.63~0.78 and N

2

content of 0.2%~0.8%.The carbon isotope of group composition and individual n-alkanes of condensate in the Awatage and Wusonggeer Formations are relatively light.The carbon isotopes of C

9

-C

23

n-alkane are -37.25‰~-32.56‰.These geochemistry characteristics indicate that the condensate oil and gas in the Awatage and Wusonggeer Formations originated from the Middle-Upper Ordovician source rocks.