江陵凹陷形成演化与勘探潜力

CONSTITUENT EVOLUTION AND EXPLORATION POTENTIAL IN JIANGLING DEPRESSION

江陵凹陷是在侏罗纪末期燕山变形褶皱基底上形成的晚白垩—下第三系的凹陷背景下的断陷盆地 ,具有NE分带、NW分块的构造格局。盆地形成演化经历了第一期伸展断陷盆地的形成 (晚白垩纪—早始新世 )、第二期断陷盆地形成 (中始新世—晚始新世 )、后期反转构造的形成及抬升剥蚀阶段 (古近纪末 )。早始新世早期新沟嘴组下段与晚始新世早期潜江组三—四段充填了半深湖—深湖相的泥岩 ,由于沉降中心相对稳定 ,潜江组优质厚层湖相泥岩构成其良好的区域盖层。构造演化控制了烃源岩、储集岩的分布及油气运移和聚集 ,油藏具有多层系晚期成藏特征 ,有利油气聚集带 :①继承性古隆起 ;②富烃洼陷周缘断鼻、断背斜型圈闭 ;③构造应力的交汇处。

Jiangling depression is a fault basin formed on the Yanshan folded basement of Late Jurassic under the depression setting of Late Cretaceous - Paleogene. The structural Pattern has the characteristics of zoning in NE and blocking in NW. The evolution of the basin can be divided into 3 stages:formation of an elongational fault basin during Late Cretaceous - Early Eocenes; formation of a fault basin buring Middle Eocene - Late Eocene;formation of a reverse structure and uplifting and erosion during Late Paleogene - Later. The mudstone with middle-deep lake facies is deposited in the lower interval of Xingouzui formation at the early stage of Early Eocene and the 3rd - 4th intervals of Qianjiang formation at the early stage of Late Eocene. The supreme thick mudstone with lake facies in the Qianjiang formation constitues a regional seal with high quality due to the relatively stable subsiding center. The distributions of source rock and reservoir rock, the migration and accumulation of hydrocarbons are controlled by structural evolution, thus the reservoirs are characterized by multi-layer series and late formation of pools. The favorable zones for hydrocarbon accumulation include: (1) inherited paleo-uplifts; (2) Peripheral fault nose and fault anticline traps of the deperession with rich hydrocarbons; (3) cross points of structural stress. The above conditions show that Jiangling depression is of splendid exploration prospects.