A comprehensive analysis of the Upper Paleozoic gas source conditions in Ordos Basin shows that high quality source rock is the major factor controlling the formation and distribution of large tight sandstone gas field in the study area.The lower limit of gas generation intensity for large tight sandstone gas field is determined based on analysis of gas production test results.A correlation analysis is first performed on the thickness

total organic carbon content (TOC) and maturity of the Upper Paleozoic source rocks in Ordos Basin

and gas generation intensity of the sources rocks is then calculated based on the correlation analysis.The calculation results are finally integrated with gas production tests to perform comprehensive analysis.The analysis of gas source conditions indicates that the Upper Paleozoic source rocks are characterized by high quality

wide distribution

high maturity

high intensity of gas generation and wide gas supply.In general

the intensity of gas generation ranges from 10×10

8

m

3

/km

2

to 40×10

8

m

3

/km

2

.However

the gas generation intensity is not equilibrium in the whole basin.It ranges from 10×10

8

m

3

/km

2

to 20×10

8

m

3

/km

2

in the western basin

whereas

it is more than 16×10

8

m

3

/km

2

in most part of eastern basin.In conclusion

high quality source rock is one of the major factors controlling the formation of large tight sandstone gas field

and it also controls the distribution of gas-water contact in the Upper Paleozoic tight sand reservoirs.As gas accumulation is closed to the source rocks and the accumulation efficiency is high

the lower limit of gas-generation intensity can be reduced to about 10×10

8

m

3

/km

2

for Upper Paleozoic quasi-continuous tight gas accumulation in Ordos Basin.