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Hydrocarbon migration and entrapment mechanisms that occur in complex carbonate pore-fissurefracture reservoirs are key problems to be solved for the effective hydrocarbon exploration and development of the lower part of an overlapped basin.The production,gas/oil ratio and the composition of crude oils and natural gas in the TZ83 Well block are high at the intersection point of the NE and NW-strike fault and decrease gradually along the ridge of the structure.A basic model of the pore-fissure-fractures system is built according to the achievements in research on carbonate karstification.Processes of the hydrocarbon migration and entrapment in this system are analyzed,which indicates that an understanding of the complexness of differential hydrocarbon migration is a key to interprete this phenomenon.Hydrocarbon must charge the nearest compartment until it can migrate further away to charge other compartments on its pathway in the complex pore-fissure-fracture system.As a result,the following two phenomenas appear:(1) Gas is enriched near the hydrocarbon injection point and drives away the oil which is enriched in compartments farther from the injection point.(2) The complex gas-oilwater relationship is controlled by the lateral connected networks.Based on this,this paper shows that the fault intersection point is the injection point of the oil and gas and that the main pathway system is distributed along the ridge of the structure.The theory of deferential hydrocarbon migration in the pore-fissure-fracture system presents two aspects:(1) In hydrocarbon exploration,the structure of the fissure-fractures system should be described first,the special distribution of gas-oil-water then predicted according to the main charging point and the main pathway system.(2) Exploration should be confined to the hydrocarbon charging point and the main pathway systems.An exploration area should not be abandoned merely due to failure in some wells.