DISTRIBUTION OF EVAPORITES AND OVER-PRESSURED RESERVOIRS IN THE SHAHEJIE FORMATION IN THE EASTERN WENLIU AREA, DONGPU DEPRESSION, BOHAI BAY BASIN
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摘要: 渤海湾盆地东濮凹陷文东地区古近系沙三段发育有2套巨厚的膏盐层段,盐岩在横向上具有分区性分布的特点,盐湖沉积中心也随时间不断迁移。在实测压力资料统计的基础上发现,地层压力在纵向上表现为浅层常压和深层超压典型结构。沙三中下亚段是超压发育主体层位,超压顶界面深度约为2 900~3 100 m,由西向东埋深增加。东濮凹陷平面压力分布的整体状态与构造格局、沉降中心对应较好。文东地区对应超压—强超压发育中心,超压的分布范围与膏盐岩的分布具有良好的对应关系。膏盐岩地层的压力和物性封闭的双重封闭机制是地层超压形成和保存的重要控制因素。膏盐岩及超压的存在对于烃源岩的发育、油气富集等具有重要的意义。Abstract: Two thick sequences of evaporites consisting of gypsum and halite occur in the Paleogene Shahejie Formation of the eastern Wenliu Area, Dongpu Depression, Bohai Bay Basin. On the plane view, the distribution pattern of the evaporites is different from region to region, mainly depending upon the frequently shifting of depocenters with time. Statistics of the measured pressures suggest that the formation pressure of the Shahejie Formation shows a "double layer structure" consisting of upper normal pressure and lower abnormal high pressure. Very high abnormal pressure mainly occurs in the middle and lower part of the 3rd member of the Shahejie Formation. The top surface of the over-pressured zone ranges from 2 900 to 3 100 m in depth and gradually rises up from the west to the east. Formation pressure is closely related to the tectonic structure and depocenter. The occurrence of abnormal pressure matches well with distribution of the evaporite rocks. It suggests that the evaporite sequences act as seals of both pressure and physical property. The double seal mechanism is the key element to the formation of the abnormal pressure in the Dongpu Depression. The evaporite sequences and overpressure have great significance to the origin of hydrocarbon reservoir and the oil and gas accumulation.
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Key words:
- over-pressure /
- distribution pattern /
- gypsum and halite /
- Bohai Bay Basin
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