Fracture Development and Accumulation History of Fractured Reservoirs in Tongnanba Belt,Northeastern Sichuan Basin

The fractured reservoirs are one of the most important prospecting targets in northeastern Sichuan Basin. However,the development features of fractures and the filling history of these fracture reservoirs were not well studied. This paper mainly analyzes the fracture characteristics by image logging and determines the charging time of gas reservoirs in Tongnanba structure belt by fluid inclusion measurements. The main conclusions can be summarized as follows. Firstly,the fractured reservoirs are mostly distributed in ooid limestone and grey doloarenite,respectively,in T1j2 and T1f3 formations,and dominate by high-angle or vertical fractures. Secondly,the trend of fractures is consistent with that of neighboring faults due to the northeast-southwest compression stress due to Daba Mountain structure and medium-late Yanshan Movement,which indicates that fractures might be formed in the era of late Jurassic. Thirdly,the gas charging time is about late Jurassic(160～148Ma) as confirmed by fluid inclusion measurements. Fourthly,it is the most important factor for the gas filling time that the development time of fractured formation matches with the gas-generating peak of the source rock in Tongnanba structure belt.