Abstract：
The exploration results show that the Dengying Formation on the North Slope of the Central Sichuan paleo-uplift has
a good exploration potential, and it is an essential area for a natural gas reserve replacement strategy in the Sichuan Basin. The
natural gas in the north slope of the central Sichuan Paleo-uplift is dry natural gas, mainly composed of CH
4
. There are obvious
differences in the carbon isotopes of C
2
H
6
, the concentration of CO
2
and the carbon isotopes of CO
2
in the natural gas in the
Dengying Formation of the north slope area. The analysis of the controlling factors leading to the differences in natural gas is of
great significance to study the accumulation and evolution process of natural gas in the Dengying Formation. Based on gas com
ponent analysis and carbon isotope analysis of the different components in the Dengying Formation natural gas from two typical
exploration wells in the north slope area, namely the Pengtan-1 and Zhongjiang-2 wells, we combined drill core description,
microscopic observation of the thin sections, carbon isotope analysis and the microstructure of the reservoir solid bitumen in the
Dengying Formation to analyze the causes for the difference in natural gas of the Dengying Formation in the north slope area of
the central Sichuan Paleo-uplift. Influenced by thermochemical reduction of sulfate (TSR), there is a high content of H
2
S in the
natural gas of the Dengying Formation in the north slope area. The carbon isotopes of reservoir solid bitumen are lighter than
that of the source rock, and the C
2
H
6
. The formation of the reservoir solid bitumen of the Dengying Formation was controlled
by hydrothermal fluid activities. Hydrothermal mineral assemblages, such as pyrite, sphalerite, and galena, are developed in the
Dengying Formation reservoir. Medium-coarse mosaic and fibrous structures are developed in the solid bitumen filling in the
reservoir of the Dengying Formation, indicating hydrothermal fluid activities in the reservoir. Hydrothermal fluid provided an
abundant sulfur source for TSR. The intensity of hydrothermal fluid activities controlled the intensity of the TSR reaction. A
relatively strong TSR reaction leads to an increase in the concentration of CO
2
, carbon isotopes of C
2
H
6
and CO
2
of the natural
gas. The difference of TSR intensity in the reservoir is the cause of the difference in natural gas from different regions.
