松辽盆地断陷期超层序界面的地质属性刻画及其油气地质意义

Geological Signatures of Sequence Boundary of the Songliao Basin: New Interpretation and their Relation to Gas Accumulation

松辽盆地断陷期分为 1个超层序组、3个超层序、6个层序。从火石岭组到营城组构成一个完整的活动大陆边缘火山—断陷超层序组。三个超层序分别为同碰撞期火山—断陷超层序 (火石岭组 )、火山间歇期断陷超层序(沙河子组 )和后碰撞期火山—断陷超层序 (营城组 )。超层序组底界 T5界面是前三叠纪拼合基底与侏罗系火山岩—沉积岩互层序列之间的反射界面 ,界面上下层系之间的间断时限≥ 4 5 Ma;界面之下是古亚洲洋构造域时期形成的拼合基底 ,界面之上是鄂霍次克洋构造域形成的火山—沉积建造。超层序组顶界 T4 界面是断陷期火山岩—碎屑岩互层序列与上覆坳陷期正常沉积岩层序之间的反射界面 ,界面上下层系之间的间断时限为 3～ 5 Ma;界面之下是鄂霍次克洋构造域晚期形成的火山—沉积建造 ,界面之上是太平洋构造域早期形成的坳陷期沉积层序。层序对油气的控制作用十分明显。高产工业气藏主要见于超层序组的顶界面 ;工业气藏和低产气藏主要出现在层序界面附近 ;

The interbedded volcanic—clastic successions, formed during faulting stage of the Songliao Basin, contain one megasequence, three supper sequences and six sequences. As components of megasequence, the three supper sequences correspond to the Upper Jurassic Huoshiling Formation (J 3h, 157~145Ma), Lower Cretaceous Shahezi Formation (K 1s, 145~130Ma) and Yingcheng Formation (K 1y, 130~113Ma), respectively. The syn-collisional volcanic—fault supper sequence (J 3h) is andesitic rocks dominant and was formed during the subduction of the Okhotsk plate. The inter-volcanism supper sequence (K 1s) is predominantly composed of coal-bearing clastic rocks and was formed during a subduction quiescence stage. The post-collisional volcanic—fault supper sequence ((K 1y) is rhyolitic rocks dominant and was formed during the late stage of the subduction of the Okhotsk plate. The bottom boundary of the megasequence is recognized with a regional unconformity representing a time interval over 45 Ma and a tectonic transform from Paleo-Asian Ocean to the Okhotsk regime. The top boundary of the megasequence is also a regional unconformity representing a time interval ca. 3~5 Ma and a tectonic transform from the Okhotsk to the Pacific regime. Some local angular unconformities covered with volcanic rocks in between the supper sequences resulted from volcanic doming, rapid eroding followed by lava covering. There are in general no significant time hiatus between the two supper sequences as the case between K 1s and K 1y. Most of the highly productive gas traps are formed at the top boundary of the faulted megasequence. Supper sequence boundaries are the second most important places for gas accumulation. Only poor gas traps have been found inside the sequences. Compared to the top boundary, only a few commercial gas pools have been discovered at the bottom boundary of the faulted megasequence, suggesting either the lack of source rocks at the deeper part of the basin or more test drilling needed there.