柴达木盆地东部侏罗纪原型盆地恢复

中下侏罗统是柴达木盆地东部中深层主力生烃层系，针对研究区前人“早-中侏罗世为广盆沉积、现今残留凹陷均有分布”的普遍认识与实际钻探的矛盾，以及侏罗系有效生烃中心不明确等问题，笔者从地面地质调查、山前冲断带构造建模入手，运用平衡剖面技术研究控凹断裂活动性及盆山演化过程，认为发育持续沉降型、构造正反转型、构造负反转型等三类凹陷；按照 “七因素法”恢复了侏罗纪各时期盆地原型，认为柴东地区发育尕西-鱼卡、红山-小柴旦、霍布逊、德令哈等4个早-中侏罗世分隔性湖盆，晚侏罗世才发展为统一沉积湖盆，纵向充填表现为早侏罗世伸展弱断陷、中侏罗世伸展拗陷湖沼相、半深湖相以及晚侏罗世挤压拗陷河流冲积相逐层超覆沉积、湖盆不断扩展的特征。中、下侏罗统有效烃源岩残留分布于原始湖盆改造后的尕西等4个持续沉降型凹陷以及鱼卡等两个构造正反转型凹陷。

Jurassic prototype basin reconstruction in east part of Qaidam Basin

The mid lower part of the Jurassic is the main source rock for mid deep buried reservoirs in the east part of Qaidam Basin. It is well accepted that “lacustrine deposits were widely distributed during the early mid Jurassic, and were still remained in the residual sags”, but this really contradicts the drilling experience. To find out the actual situation, and confirm hydrocarbon kitchen, the author carried out surface geological survey and structural modeling for the thrust belt in mountain front, and also studied activities of faults that controlled development of sags and evolution of basin range by means of balanced sections. Results indicated that there are three types of sags, namely continuing subsided sag, positive inversed sag, and negative inverted sag. Prototype basin during different epoches in the Jurassic was reconstructed according to “seven factors method”. Four separated lake basins were developed during the early mid Jurassic, they were Gaxi Yuka, Hongshan Xiaochaidan, Huobuxun, and Delingha, respectively, and then they developed into a unified basin during the late Jurassic epoches. Vertically, the early Jurassic is featured by weak elongated fault subsidence, the middle Jurassic is featured by extension downwarped swamp limnetic facies, and the late Jurassic is featured by compression downwarped fluvial alluvial facies. Remnant source rock in the mid lower Jurassic was distributed in 4 reworked continuing subsided sags such as Gaxi, and 2 positive reversed sags such as Yuka.