内蒙西部银根-额济纳中生代盆地群叠置类型与勘探领域

内蒙西部银根-额济纳盆地群是在前古生代基底上发育起来的中、新生代“叠置型”盆地群。构造演化经历了三叠纪的热拱隆张阶段、早中侏罗世的初始裂谷盆地阶段、早白垩世的裂谷盆地发育阶段、晚白垩世的引张坳陷阶段、第三纪到第四纪的陆内聚敛挤压阶段。主要形成了下白垩统半深湖相烃源岩,其次为中下侏罗统煤系烃源岩。根据构造层之间的叠置关系,可划分为完全叠置型、基本叠置型、迁移叠置型3种盆地(凹陷)类型。不同叠置类型盆地(凹陷)的烃源岩发育特征、各类圈闭发育特征不同,油气成藏条件差别较大,勘探方向和勘探领域不同。根据裂谷小湖盆的沉积发育特征,应围绕沉积“洼槽”中心的烃源岩开展近源勘探,分别指出了不同叠置型盆地(凹陷)的勘探领域:叠置型盆地(凹陷)主要以控盆断裂带的滚动背斜、缓坡带的岩性、地层不整合圈闭为主要勘探领域;基本叠置型盆地(凹陷)主要以中央断裂隆起构造带的断鼻、断块圈闭为主要勘探领域;迁移叠置型盆地(凹陷)主要以不整合圈闭和缓坡带的岩性圈闭为主要勘探领域。

Superposed Basin Types and Exploration Realms in Mesozoic Yingen-Ejina Basins in the West of Nei Mongol

Yingen-Ejina Basins in the west of Nei Mongol is shown by superposition of Mesozoic and Cainozoic on basement of pre-Palaeozoic constitutes. Its evolution of the tectonism include hump and fission in high temperature stage in Triassic, initial rift valley devopment stage in the Early and Middle Jurassic, rift basin devopment stage in the Early Cretaceous, open and sag stage in the Later Cretaceous and convergent and extruding stage in continent from Tertiary to Quaternary. In these process of evolution, it deposited mainly hydrocarbon source rocks of lacustrine facies in the Early Cretaceous and secondary coal measures source rocks in Early-Middle Jurassic. The basin can be divided into three types such as entire superposition, basic superposition and displaced superposition according to the superposition correlation among of the tectonic layers. The character of hydrocarbon source rocks and the development character of traps may be different by all types of superposition basin. And the difference of the hydrocarbon accumulation condition is great. The direction and realm of exploration are different too. We should make some exploration around the hydrocarbon source rocks in middle of sedimentation groove based on character of sediment development in small rift lake basin. The thesis pointed out the exploration realms of all types of superposition basin: The exploration realms of entire superposition basin are roll anticline of fracture zone controlling basin, lithologic trap and stratigraphic unconformity trap on gentle slope zone. The exploration realms of basic superposition basin are flault nose and flault block trap of central fracture and ridgy zone. The exploration realms of displaced superposition basin are lithologic trap on gentle slope zone and stratigraphic unconformity trap.