The groundwater in the Tertiary Chengbei fault terrace zone in the Dagang oilfield is considered to be mildly saline water.The contents of positive ions are characterized by Na

+

+K

+

>

Ca

2+

>

Mg

2+

and the contents of negative ions feature in Cl

-

>

HCO

3

-

>

SO

4

2-

>

CO

3

2-

.The Cl

-

controls the total ion content.The salinity of groundwater shows obvious vertical zonations.The high salinity NaHCO

3

water is the main type and distributes widely in the study area.According to the vertical change of salinity and chemical compositions of the groundwater

three types of hydrochemical profiles could be recognized

including positive type

reversed type and multi-directional type.The reversed and multi-directional type profiles reflect that the vertical connectivity is fine

ma-king it good for hydrocarbon migration.Based on the vertical distribution of parameters such as salinity

ion content

Na

+

-Cl

-

ratio and coefficient of desulfurization

we have divided the hydrochemical dynamical zones into three types:the formation water exchange smooth zone

the exchange retardation zone and the exchange dilatoriness zone.Usually under the fluid compartment and with relatively high salinity

the exchange dilatoriness zone is considered rich in oil and gas.Therefore

we have predicted that the Shahejie Formations in the Zhangdong and eastern Zhangdong areas are favorable exploration targets.