银根—额济纳旗盆地查干凹陷构造-沉积格架与油气勘探方向

STRUCTURAL-DEPOSITIONAL FRAMEWORK AND HYDROCARBON EXPLORATION PROSPECTS IN THE CHAGAN DEPRESSION,THE YINGEN-EJINAQI BASIN

银根—额济纳旗盆地是一个发育在兴蒙海西褶皱带上的白垩纪走滑 -拉分盆地 ,凹隆相间的盆地结构 ,使得各个凹陷具有多物源和近物源的特点 ,三角洲 -滨岸沉积体系十分发育 ,对油气成藏起着重要的作用。查干凹陷是其东北部一个重要的沉积单元。研究表明 :凹陷断陷期 (K1 b—K1 s)火山作用强烈、地温梯度高 (4 .8℃ / 10 0m)、沉积厚度巨大 ,主要勘探目的层 (K1 b—K1 s1 )的成岩作用早而强烈 ,储层物性较差 ,主要为特低孔、渗储层 (Ⅳ、Ⅴ类 )。因受燕山Ⅳ幕运动 (K1 s末 )的强烈改造和差异剥蚀 ,使得早期原型盆地的构造、地层格架发生了明显的变化。因此 ,恢复原型盆地及时空展布 ,寻找受古隆起控制的同生继承性构造 ,是查干凹陷解决较差储层制约因素和寻找油气富集的重要途径之一。而其中受古隆起背景和沉积体系双重控制的有利储集相带是形成查干凹陷油气局部富集的重要制约因素 ,这种构造

Developed on the the Xing Meng Hercynian Folded Belt, the Yingen Ejinaqi Basin is a Cretaceous strike slip one with coexisting of rags and highs in the structure. Each sag is characteristic of multiple and near provenance fillings with delta and coastal depositional systems extremely developed, and the latter surely played an important role in the formation of oil and gas reservoirs in this basin. The results illustrated that the Chagan Depression is a most important sedimentary unit lying in the northeast of the basin, and the features of the basin are strong volcano activity, high geothermal gradient (4.8℃/100m) and large sedimentary thickness during the period of rift faulting (K 1 b - K 1 s ). The diageneses in the target reservoirs (K 1 b - K 1 s ) occurred early and strongly, which resulted in the low porosity and permeability of reservoir properties (type Ⅳ/Ⅴ). Moreover, due to subjected to reformation and uneven erosion in the forth episode of the Yanshanian event (in the end of K 1 s ), the structural and stratigraphic framework of the primary basin had been changed obviously. Therefore, to resume the proto basin and its distribution and then to seek the syngenetic successive structures principally controlled by paleo highs should be one of the solutions to looking for the rather good reservoirs and potential petroleum accumulation zones. This favorable reservoir zones are believed to be the controlled by the development of both paleo highs and depositional systems, while the structural stratigraphic traps will be the main targets for the further exploration.