ACCUMULATION PATTERN AND ENRICHMENT LAWS OF SUBTLE HYDROCARBON RESERVOIRS IN BIYANG SAG, NANXIANG BASIN

The Biyang Sag in the Nanxiang Basin is very favorable for hydrocarbon accumulation.Formation and development of the sag are controlled by 2 deep-large faults in the south.Superior oil generation conditions,abundant sediment resources,development of sand body,good reservoir conditions,good source-reservoir-cap rock assemblage and multiple trap model configurations are favorable for accumulation.Subtle oil and gas reservoirs can be divided into 5 major types and 19 subtypes.In plane,reservoirs locate in circles,controlled by source sag.Vertically,they are influenced by temperature and pressure.Displacement sections of large boundary faults are favorable for large-scale sandstone pinch out reservoir.Inherited sedimentary-tectonic slopes are the targets for large-scale hydrocarbon migration.Oil and gas us-ually accumulate in nose-like uplifts.Deep sags are favorable to find low system trace fans,dolomite oil and gas reservoirs and deep-basin oil and gas reservoirs.Controlled by geometrical patterns,rollover faults can be found at the 2 ends of boundary fault.