Abstract: 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.

Key words: slip fractured zone, induced frature zone, fault sealing capacity, Xiahong North Fault, Junggar Basin