Jiyang depression

one of the important petroliferous depressions in Bohai Bay Basin of eastern China

has the most complex and diverse pressure systems.Based on statistics of the measured pressures

log responses of mudstone overpressures and characteristics of over-pressure profiles of many sags in Jiyang depression

we divide the overpressure systems in Dongying

Chezhen

Zhanhua and Huinin sags into three types

namely the single high overpressure system

the compound overpressure system and the single low overpressure system.The single overpressure system distributes laterally in Dongying and Chezhan sags and occurs vertically as one overpressure zone in overpressure Es

3

-Es

4

with a relatively large overpressure amplitude and a pressure coefficient over 1.8.The compound overpressure system distributes laterally in Chezhen sag and occurs vertically as three separate overpressure zones in Es

1

Es

3

and Es

4

respectively.The single low overpressure system distributes laterally in Huimin sag and occurs vertically as only one overpressure zone in Es

3

with a comparatively small overpressure amplitude and a pressure coefficient less than 1.4.The dissimilarities of the overpressure structures in different sags are closely related to the sequences and the thermal maturities of source rocks

the distribution of pressure sealing layers

and the fault activities

in the sags.The distribution and thermal evolution of source rocks control the formation and distribution of the overpressure system.The pressure sealing layers control the top and bottom boundaries of an overpressure system.The deep-rooted faults control both the inside and outside horizontal boundaries.