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The Yitong (伊通) basin is a Late Mesozoic and Cenozoic continental sedimentary basin in Northeast China. On the basis of well tests and seismic data, we use the 2D modeling technique to rebuild the pressure evolution and hydrocarbon migration in the Moliqing (莫里青) fault depression of the Yitong basin. Based on the modeling results, four conclusions are drawn as follows. (1) The Eocene Shuangyang (双阳) Formation within the Moliqing fault depression had entirely undergone three episodic cycles of pressure accumulation and release in geological history, and the three tectonic movements since the Middle Eocene played important roles in the episodic changes of excess pressure. (2) The present formation pressure distribution is characterized by normal pressure in almost the entire fault depression with some residual overpressure. The differential distribution of pressure results mainly from the difference in rock facies, sedimentation rate, hydrocarbon generation, and fault activities. (3) The hydrocarbon migration is more active during the release of pressure in the Moliqing fault depression, which happened mainly in the Middle-Late Oligocene and provided the driving force for hydrocarbon migration. (4) The hydrocarbon migration was mostly directed to the Shuangyang Formation within the Jianshan (尖山) uplift and the Kaoshan (靠山) sag. With the superior condition of hydrocarbon accumulation and the higher degree of hydrocarbon concentration, the northwest part of Kaoshan sag is considered a favorable area for oil and gas exploration in the Moliqing fault depression. KEY WORDS: Yitong basin, basin modeling, tectonic movement, pressure evolution, hydrocarbon migration.

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Low exploration activity fields (e.g., deep formation, deep water, and new exploration areas) are of great importance for petroleum exploration. The prediction of source rocks is critical to the preliminary evaluation of low exploration activity fields, which will determine the early strategic electoral district and decision of exploration activity. The northeast depression is a new exploration area at the South Yellow Sea basin at present. Based on lots of seismic data in the study area and a few of well data in adjacent homologous depression, the early evaluation of source rock in the northeast depression was finished by comprehensively using the techniques of geological analogy, geophysical inversion and basin modeling, and an integrated methodology about preliminary evaluation of source rocks to low exploration activity fields is also presented. The methodology consists of three aspects: (1) prediction of the main formation of major source rocks, based on analogy analysis of seismic reflection characteristics and quality of source rocks in adjacent homologous depression; (2) method of seismic attribution to determine the thickness of source rocks; and (3) prediction of vitrinite reflectance, based on basin modeling technique to determine the maturation of source rocks. The results suggest that the source rock of the Taizhou (泰州) Formation is the most important interval for hydrocarbon generation in the northeast depression, which is characterized as high TOC, fine OM type, huge thickness, and high maturity. The western subdepression is the most important hydrocarbon kitchen in the northeast depression.