In order to understand the fracture characteristics of reef-bank reservoir in the Changxing Formation in Yuanba area

northeastern Sichuan Basin

this paper finely described the fractures of the Changxing Formation in many wells

and also studied the tectonic evolution

hydrocarbon generation

diagenesis and the porosity evolution.Vertically

the fractures are mainly distributed in the 2

nd

Member of Changxing Formation.While laterally

they show strong heterogeneity in distribution

with heterogeneity being different in different blocks.Fractures are relatively well developed on structural high.The fractures can be divided into 3 types and 11 subtypes developed mainly in 3 stages.We established the classification evaluation index system and the standard identification chart of typical fractures.The formation of fractures is mainly controlled by the tectonic evolution

burial and dissolution.The dynamic fracture-pore assemblages of the 2

nd

and 3

rd

stages are better than that of the 1

st

stage.These assemblages form effective storage space or reticular carrier systems and make a positive contribution to the reservoir property and productivity.The comprehensive analysis indicates that the Changxing Formation in the northwestern Yuanba area is favorable for enrichment of oil/gas.