济阳坳陷优质烃源岩特征与隐蔽油气藏的关系分析

通过对济阳坳陷优质烃源岩的研究,尝试建立勘探中、后期烃源岩研究的流程和工作方法。结合大量的分析资料,建立了本区优质烃源岩的评价标准,该标准可适用于中国的陆相断陷湖盆研究。对烃源岩的生排烃特征模拟结果表明,普通烃源岩、优质烃源岩以及有机质富集层三种不同类型的烃源岩生烃时间基本相同,但在排烃方面三者区别较大,普通烃源岩开始排烃最晚,优质烃源岩次之,而有机质富集层则最早进入排烃阶段。本区优质烃源岩的分布与隐蔽油气藏密切相关。沙四上亚段和沙三下亚段是本区广泛分布优质烃源岩的重点层位,它们与隐蔽油气藏的关系非常密切。优质烃源的分布直接或间接地决定了隐蔽油气藏勘探的成功率。对东营凹陷和沾化凹陷已经发现的隐蔽油气藏油气源的分析结果表明,在沾化凹陷,隐蔽油气藏主要以沙三段下部优质烃源岩为主。但罗家油田原油则是以沙四上亚段和沙三下亚段的碳酸盐岩源岩层所生成的混源油为主。沙四上亚段烃源岩主要形成地层性的隐蔽油气藏,而沙三下亚段烃源岩和沙四上亚段烃源岩均可以形成岩性型油气藏。在此基础上,建立了坳陷不同位置与其烃源岩和油气运移特点相关的隐蔽油气藏形成模式图。

The excellent source rocks and accumulation of stratigraphic and lithologic traps in the Jiyang depression, Bohai bay basin, China

The excellent source rock is a very important source rock and plays a major role in the accumulation of stratigraphic and lithologic traps.As the evaluation standard and definition of excellent source rocks are different,the appraisal parameters of excellent source rock have been tentatively established.The excellent source rocks in the Jiyang depression may be divided into three categories:oil shale;marl;mixture of oil shale and marl,which belong to EsU4 and EsL3 stratigraphic unit.They are mainly distributed in the center of sag and in tectonic slope break.They also may be found in the slope of abrupt slope and gentle slope of the depression.Geological and geochemical research shows that the excellent source rock is the key factor for the subtle oil and gas accumulation.The results of basin simulation also prove that the excellent source rock is at early stage for oil expulsion.The distribution of SPI index reveals the close relationship between the excellent source rock and the subtle oil and gas accumulation.The major source rocks of stratigraphic and lithologic traps have been analyzed.Although EsU4 and EsL3 stratigraphic units both can be source rocks of subtle traps,the major source rocks of stratigraphic and lithologic traps are different.The stratigraphic traps are mainly derived from EsU4 unit and lithologic traps are mainly derived from EsL3 unit.They are closely related to the sequence stratigraphic framework of source rock.Actually,the ancient water level of EsU4 unit is varied and EsU4 belongs to TST unit;EsL3 mainly belongs to TST and HST unit.An oil accumulation model has been proposed in this paper.