Natural gas in Hetianhe gas field

which is distributed in an elongated E-W direction as a whole

have been sourced by the high-and over-mature Cambrian source rocks.The components of natural gas in Hetianhe gas field have the following characteristics: C

2

/C

3

decreases with increasing C

1

/C

2

variation of carbon isotope value of δ

13

C

2

-δ

13

C

3

is relatively large

while variation of ln(C

2

/C

3

) value is relatively small.According to the conventional diagnostic criteria of kerogen cracking gas and secondary cracking gas from oil

the gas in Hetianhe gas field should be of kerogen cracking gas.The dry coefficients

methane carbon isotope values and CO

2

contents of natural gas are obviously different in the western and eastern wellblocks of Hetianhe gas field.Accompanying the formation of Hetianhe trap in late Himalayan

the kerogen cracking gas migrated from the high pressure zone in the east to the low pressure zone in the west in the form of dissolved gas.The solubility of methane in water is larger than that of heavy hydrocarbons

the solubility of δ

13

CH

4

is larger than that of δ

12

CH

4

)

and CO

2

has the largest solubility among the components of natural gas

all these would lead to the fractionation of natural gas components and methane carbon isotope.As a result

the natural gas in the western wellblock is characterized by larger dry coefficient

heavier methane carbon isotope and obviously higher CO

2

content.