There are two kinds of oil field water(CaCl

2

and NaHCO

3

) in Yanqi basin

the water mineralization is 5.5～73.2/1

presenting in forward water chemical section character with apparent zoning. CaCl

2

type is mainly distributed in northern area of Baobei block

in Baolang Sumu structural belt

whereas NaHCO

3

is chiefly distributed in the blocks of Baonan

Benbutu

Zhongmachang as well as some areas of Baozhong block. Organic mater abundance in oil field water is lower(below 2×10

-6

) while organic acid content is very high(2546×10

-6

～5148×10

-6

and acid content is usually 0.12×10

-6

～4.63×10

-6

. Therefore

it is confirmed that there are three hydro-geologic belts in the basin namely; free alternative belt

slow alternative belt and hindered belt

and the preserving condition in the north is better than that in the south and central part is better than that in the edge of the basin.