海拉尔盆地乌尔逊凹陷中的三角形断块：演化及对油气的控制作用

在乌尔逊凹陷中部发育一个三角形断块，因边界断裂的同沉积活动而使断块沉陷深，沉积厚度大.晚期的构造反转使整个三角形断块向上冲断，尤以北界断裂的冲断活动表现强烈.三角形断块为各时期的沉积中心，控制着深湖相和湖底扇沉积的发育；烃源岩的类型也与三角形断块有关，块内为Ⅰ型和Ⅱ型干酪根，边部和外部为Ⅱ型和Ⅲ型十酪根.南屯组的有效烃源岩在乌尔逊断陷分布范围较大，主力烃源岩只局限于三角形断块内.晚期反转时北界断裂有利于构造圈闭的形成，反转断层也为油气的运移提供了通道.因此，三角形断块在生储盖层的发育和油气生成、运移与聚集的空间配置关系上可谓得天独厚，是最有利的油气聚集区.

Triangle fault-block in the Orxon Sag, Hailar Basin: Evolution and its controlling action to hydrocarbon

There occurred a triangle fault-block in the central Orxon Sag, Hailar Basin, with the boundary faults being NEE-striking, NE-striking and N-S orientation faults respectively.The triangle fault-block was depositional center in formational stage of the Orxon Sag, with the northern boundary fault being a syndepositional normal one.The western and eastern boundary faults became transfer ones during the period of Nantun and Damoguaihe Formations'deposition.The fault-block upthrust violently when the basin reversed, and the northern boundary fault played a more important role in thrusting and folding.The triangle fault-block not only controlled the interior sediments of deep lacustrine facies, but also controlled developing of sublacustrine fans and distribution of dark mudstones.The kerogen types of source rocks connected closely with the triangle fault-block, namely, the types Ⅰ and Ⅱ in the interior, types Ⅱ and Ⅲ along the boundary faults,and type Ⅲ outside the block.The available source rocks in Nantun Formation was limited in the central trianglar region in the Orxon Sag.The later reverse structures, indicated by two unconformities,were favourable to create the structural traps,and the reversed faults became pathways of the oil-gas migration.The drilling pratice revealed that the Wuzhong(Central Orxon) triangle fault-block was a more interesting area for oil-gas exploration in the Hailar Basin.