Exploration and Development Research Institute��Northeast Oil and Gas Branch��SinoPEC��Changchun 130062��China

The half-faulted Zhangwu Basin is one of the typical low-degree exploration areas among the depressions in southern Songliao Basin�� Three boreholes and new 2D seismic data are used to analyze petroleum geologic features and oil-gas accumulation conditions of the studied area�� The results show that there are favorable source-reservoir-cap assemblages in Shahai and Jiufotang formations�� such as‘self-generation with self-accumulation’��‘ lower-generation with upper-accumulation’and‘upper-generation with lower-accumulation’�� Favorable source-reservoir-cap assemblages��lateral sealing by faults and near-source conditions are controlling factors of petroleum accumulations in this area��primarily forming structural-lithologic reservoirs��Organic matters of source rocks in Shahai Formation are mainly ��B type��and the Ro ranges between 0. 5% and 0. 7%��indicating a low maturity stage�� Organic matters of source rocks in Jiufotang Formation are mainly �� and ��A in type and the Ro ranges between 0. 7% and 1. 0%��indicating a maturity stage�� Reservoir rocks in Shahai Formation have middle porosity and low to middle permeability��while those in Jiufotang Formation have low porosity and very low permeability�� Mudstone in the top of Shahai Formation is similar to regional cap rocks��and mudstone in the top of Jiufotang Formation provides direct sealing�� As source rocks are with higher quality and reservoir rocks with higher proportion��there is greater potential for petroleum accumulations in Jiufotang Formation��which can be selected as target priority for the future exploration��