Abstract: With the development of petroleum exploration, the importance of lithologic reservoir is becoming more and more obvious. The key to lithologic reservoir exploration is to clarify the enrichment law of hydrocarbon. A large number of lithologic reservoirs are developed in the middle third Member of Shahejie Formation in Niuzhuang sub-sag. In this study, the authors focused on the analysis of the main controlling factors on the horizontal accumulation. The results show that the distribution of oil and gas reservoirs in Niuzhuang sub-sag is controlled by three geological factors:fluid property, faults and sedimentary facies in the sub-sag. Their effects on the enrichment of lithologic reservoirs in the sub-sag are:1) the fluid migration and accumulation units control the enrichment zone of oil and gas in the plane, i.e., the north-south confluence units is favorable for petroleum accumulation, while the parallel of the north and the divergence flow units in the east and west area of the sub-sag are unfavorable; 2) the pump-absorb action of syngenetic fault makes it possible for oil and gas to form local convergent flow in the parallel or the divergence flow units developing area, thus reservoir develops; the lateral shelter action of fault makes oil and gas accumulate in the inner side of the boundary fault; 3) in all the sedimentary facies, turbidite channels with good storage quality are the best for hydrocarbon accumulation, lobe and the middle channels are the second, and peripheral areas are the worst.

Key words: lithologic reservoir, middle third Member of Shahejie Formation, fluid potential, faulting, sedimentary facies, Niuzhuang sub-sag, Bohai Bay basin