T72界面与塔中隆起上奥陶统碳酸盐岩古岩溶储层

The seismic reflection boundary T72 and the Upper Ordovician carbonate karst reservoirs on the Tazhong uplift, Xinjiang

关键词:  地震反射界面  T₇²界面  塔中隆起  碳酸盐岩

Key words:  seismic reflection boundary  T27 boundary  Tazhong uplift  carbonate rock

摘要:

T₇²界面为上奥陶统桑塔木组泥岩与良里塔格组灰岩地震反射界面,是塔里木盆地塔中、塔北隆起上奥陶统内部的一个重要构造-层序转换面,是早古生代碳酸盐台地型沉积向陆源碎屑充填沉积转换的标志。过去普遍认为两个组之间为连续沉积,界面性质系海侵上超并赋予“淹没台地”的涵义。但随着近年塔河油田南部地区的勘探和塔中隆起区北缘Ⅰ号断裂带油气富集规律性的深入研究,表明T₇²界面是一个区域性的古暴露界面和沉积间断界面。界面之下的上奥陶统良里塔格组顶面有明显的削蚀和截切现象,残存厚度在塔北、塔中之间存在极大的差异,反映塔北隆起T₇²界面的构造及风化壳岩溶作用明显强过塔中隆起。古暴露和风化壳岩溶作用导致T₇²界面之下的良里塔格组碳酸盐岩广泛发育岩溶,是塔中低凸起北缘Ⅰ号断裂构造带的主要油气藏聚集层位;在塔河南部,形成了一套厚度最大可达300m并贯穿良里塔格组与下伏恰尔巴克组、一间房组和鹰山组的古岩溶洞穴系统,造就了塔河油田今天以南部斜坡区上奥陶统良里塔格组灰岩古岩溶洞穴系统为主要油气储层的勘探大场面。

Abstract:

The seismic reflection boundary T₇²,i.e.,the boundary of the Upper Ordovician Sangtamu Formation and its underlying Lianglitag Formation is interpreted as an important structural-sequence transform boundary in the Upper Ordovician strata on the Tazhong and Tabei uplifts,Xinjiang,and represent the trasition from the Early Palaeozoic carbonate platform-type deposits to terrigenous clastic deposits.The deposits in the two formations cited above were previously assigned to the continuous deposits,and the boundary between them considered as a transgressive onlap and "drowned platform".The studies in recent years show that the T₇² boundary is a regional fossil exposue surface and depositional break.The truncation is well defined at the top of the Upper Ordovician Lianglitag Formation below the boundary,and the residual thickness ranges nearly from 20 m to 600 m,respectively in the Tabei and Tazhong Basins.The fossil exposure and karstification of the weathering crust permit the development of the karsts in the carbonate rocks from the Lianglitag Formation.These karsts occur as major hydrocarbon reservoir horizons along the F1 fault on the northern margin of the Tazhong uplift.A succession of about 300 m-thick palaeokarst cave systems may be traced across the Lianglitag Formation and its underlying Qarbag Formation,Yijianfang Formation and Yingshan Formation on the southern bank of the Tarim River.These palaeokarst cave systems constitute the magnificent hydrocarbon reservoir rocks composed mostly of the limestone palaeokarst systems from the Upper Ordovician Lianglitag Formation on the southern slope of the Tahe Oil Field.