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摘要: 构造-热演化史是认识盆地形成及其动力学机制的重要窗口,也是烃源岩成熟生烃研究的核心问题。随着能源需求的增长以及陆地油气发现难度的增加,海域逐渐成为我国油气勘探的重要接替区与国家能源战略研究的重要领域。秦南凹陷位于渤海海域西北部,勘探前景良好但勘探程度低。文章选取秦南凹陷3条地震剖面建立25口人工井,进行了构造沉降史和热史模拟,恢复了凹陷构造-热演化历史。结果表明:秦南凹陷新生代以来于孔店组-沙四段沉积时期(65-42 Ma)、沙三段沉积时期(42-38 Ma),以及东三段沉积时期(32.8-30.3 Ma)经历了三期裂陷拉张,总拉张系数为1.27~2.05。对应三期拉张,凹陷基底热流经历三期升高,在东三段沉积末期(30.3 Ma)达到峰值64.0~89.0 mW/m2,之后逐渐降低至今。秦南凹陷构造-热演化过程与断裂活动具有良好的耦合关系,多期裂陷加热事件有利于其烃源岩成熟生烃。Abstract: Tectono-thermal history is not only important to understand basin evolution and its geodynamic mechanism, but also the key question to be solved for source rock maturation study. With the increasing energy demand and difficulty in oil and gas discovery on land, sea basin has gradually become an important replacement area for oil and gas exploration and a hotspot of the national energy strategy research. Qinnan Depression is on northwest of the Bohai Sea area, with good exploration prospects but low exploration degree. In this study, 25 artificial wells have been established based on 3 seismic profiles in the Qinnan Depression, and then their tectonic subsidence history and thermal history has been modeled to reconstruct the tectonic-thermal evolution history of this depression. The results indicate that since the Cenozoic era, the Qinnan Depression has undergone three stages of rifting and stretching during the sedimentary periods of the Kongdian Formation to fourth member of the Shahejie Formation (65-42 Ma), the third member of the Shahejie Formation (42-38 Ma), and the third member of the Dongying Formation (32.8-30.3 Ma), with a total stretching factor of 1.27~2.05. Corresponding to the three stages of stretching, the basal heat flow of the Qinnan Depression has experienced three stages of increase, reaching a peak of 64.0~89.0 mW/m2 at the end of the deposition of the third member of the Dongying Formation (~30.3 Ma), and then decreased gradually until present. There is a good coupling relationship between the tectonic-thermal evolution process and fault activity in the Qinnan Depression, and multiple stages of heating are conducive to the mature and hydrocarbon generation of its source rocks.
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Key words:
- Bohai Basin /
- Qinnan Depression /
- structure subsidence /
- thermal history
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