黄骅坳陷歧口凹陷古近系烃源岩主要生烃特点

Hydrocarbon Generation of Paleogene Source Rocks in Qikou Sag

黄骅坳陷歧口断陷湖盆沉积岩厚度大,地层分布范围广,由于盆内、盆外物源十分发育,构造活动频繁,使其沉积环境和沉积体类型丰富多样,烃源岩除湖相泥岩外,还发育较大范围的油页岩,且在油页岩主要发育期,在一定程度上因受海水影响而具有藻类勃发的条件,在油页岩和钙质页岩中发育一定的颗石藻;针对歧口凹陷烃源岩,以"富烃源岩生烃理论"为指导,对烃源岩进行分级评价,认为歧口凹陷具有烃源岩厚度大、有机质类型丰富、有机质丰度高、优质烃源岩发育的特点;同时,由于异常超压的发育,烃源岩的成熟门限偏深,有效生油井段长,与一般的烃源岩相比生油下限明显向深部偏移,因而也使得大量生气门限较深,有效生气期作用时间短,具有"持续生油、集中生气"的特点,歧口凹陷的这种生烃热演化特征对中深层油气的分布具有明显的控制作用。

The sedimentary rock distributes extensively with large thickness in the Qikou rifted basin.As a result of provenance development both inside and outside the basin and frequent tectonic movements,the sedimentary environment and depositional systems are various.In the sag,the widespread oil shale is developed with exception of lacustrine shale.During the period of oil shale formation,the coccolithophorid in the oil shale and calcareous shale was developed,since the algae mass growth occurred under the sea water function.Based on the theory of hydrocarbon generation for hydrocarbon-enriching source rock,we classify the source rocks in the Qikou sag.The source rocks in the Qikou sag are characterized as large thickness,organic matter type and abundance of organic matters.Also,as a result of over pressure developed in the deep formation,the depth for the mature threshold of source rock is big with long hole section under the abnormal over pressure.Therefore,the depth for the threshold of large oil and gas generation is larger than that of general source rock.So the time of gas generation is short,with sustained oil generation and centralized gas generation.The characteristic of thermal evolution obviously controls the distribution of deep oil and gas formation in the Qikou sag.