Abstract：
In order to systematically and deeply study the gas source, diagenesis stage and accumulation process of the upper
Paleozoic Shanxi Formation in Taikang and the Bengbu Uplift in the Southern North China Basin, this paper adopted the crystal
linity of illite, fluid inclusion petrography, and Micro-Laser Raman, combined with rare gas isotopes, which provides a detailed
study of the diagenesis stage of sandstone, the accumulation process of tight sandstone gas and its source and contribution rate.
The crystallinity of illite in the sandstone ranges from 0.64 to 1.06 (
△
2θ), indicating an early to middle diagenesis stage. The
smectite content in the I/S mixed layer ranges from 0 to 50
%
, indicating a middle diagenetic stage A-B. The temperature of fluid
inclusions is in two ranges of 110~120 ℃ and 130~150 ℃, which also indicates in the middle diagenetic stage A-B. Integrating
the three research methods of illite crystallinity, smectite content in mixed layer I/S and paleo-temperature, the diagenesis
stage of tight sandstone in the Shanxi Formation is in the middle diagenetic stage A-B. Through fluid inclusion petrographic
observations combined with Micro-laser Raman testing, the type, composition, and generation relationship of the inclusions
are accurately determined, and there is only one hydrocarbon accumulation period. Using the homogenization temperatures
of the hydrocarbon-bearing brine inclusions, “projecting” these onto the burial history map with paleotemperature evolution,
the accumulation time of tight sandstone gas in the Shanxi Formation is determined to be the end of the Indosinian to the early
Yanshan period. By using rare gas isotope
40
Ar/
36
Ar values to calculate the age of the gas source rock, it is determined that the
natural gas in tight sandstone in the Shanxi Formation comes from the Carboniferous-Permian. According to the mud shale and
coal rock two-end-member mixing model, the contribution rate of natural gas produced by different source rocks to natural gas in
sandstone samples was calculated. The results indicate that the main source rock of natural gas in tight sandstone of the Shanxi
Formation in the southern north China Basin is the mud shale, and the contribution rate of shale is about 73
%
. Coal rock plays a
secondary role in the entire hydrocarbon generation process, and the contribution rate is about 27
%
.
