A fault is not only a planar surface

but a 3D geologic body with complex internal structures some time

which can be divided into several units.Each unit has a different sealing mechanism

thus should be evaluated with different methods.Through integration of core observation with seismic interpretation

the Xiahong North Fault is divided into two segments

an east and a west segment

in plain view

two units

a slip fractured zone and a induced fracture zone

in sectional view.The slip fractured zone experienced strong compression

twisting and abration

resulting in strong cataclasis

thus can be quantitatively evaluated by the indices of ‘Fault Surface Stress'

‘Shale Gouge Ratio' and ‘Fault Zone Filling'.The induced fracture zone experienced relatively weak cataclasis and had highly-developed fractures

better poroperm properties

thus can be analyzed according to diagenetic cementation and oil thickening by using thin section and SEM technologies.For the slip fractured zone of Xiahong North Fault

the west segment presents better sealing properties than the east segment

while for the fractured zone

the west segment is sealed by cementation and the east segment is filled by thickened oil.The SEM and fluid inclusion analyses suggest that there are at least three periods of fluid migration affecting the properties of the Xiahong North Fault

of which the 1

st

fluid migration is dominated by formation water and the 2

nd

-3

rd

fluid migration is accompanied by hydrocarbon migration.Therefore

the sealing properties of the Xiahong North Fault zone are the result of the multiple fluid activities in geologic history.