Marine shale gas resources are abundant in Southern China

and nitrogen (N

2

) content accounts for a larger proportion in the composition of some shale gas.Analytical data of the geological and geochemical characteristics of shale gas in southeastern Sichuan

Three Gorges Region of Yangtze River

and Cengong in Guizhou Province

and the thermal simulation experiment of gold tube

are integrated in the study of the origin of nitrogen in shale gas and its indicative significance.The results show that N

2

in shale gas is typically of organic crustal origin

shale gas with higher N

2

content is mainly derived from the late pyrolysis of kerogen

and the higher content of N

2

is just an embodiment of the early gene-ration of crude oil cracking gas under no migration and accumulation or under destruction after accumulation.Therefore

the fact that shale gas resources are limited may be verified by the following three aspects.First of all

the shale kerogen is typically of saprolite.Under good preservation conditions

the shale gas is supposed to be dominated by crude oil cracking gas.However

the identification of shale gas types indicates that the shale gas with higher N

2

content belongs to the kerogen pyrolysis gas or a mixture of crude oil cracking gas and kerogen pyrolysis gas.Secondly

the carbon isotope value of shale gas with higher N

2

content is significantly heavier than that of the secondary cracking gas of crude oil obtained by thermal simulation experiment

through the gold tube thermal simulation experiment of the crude oil samples taken from the Cambrian.Finally

with the growth of organic matter evolution

the N

2

content keeps increasing

and the shale gas wells with better preservation conditions are usually lower in N

2

content but better in gas-bearing properties.Therefore

the N

2

content is of indicative significance to the preservation conditions.