塔里木盆地主要山前带差异构造变形及对油气成藏的控制

塔里木盆地库车、塔西南和塔东南山前带在构造变形和活动强度等方面存在较大的差异性,这也决定了油气地质条件与油气分布的不均衡性。通过对3个山前带地质剖面的对比研究,结合对典型成藏模式的剖析,探讨山前带差异构造变形特征对油气成藏的控制作用。库车山前带以逆冲推覆及盐构造为主,构造圈闭规模大、幅度高;主要有盐下和盐上两种成藏模式,通源断裂十分发育,库姆格列木组膏盐岩对盐下油气的保存非常有利。塔西南山前带变形分段特征明显,包括三角带构造、双重逆冲、叠加背斜等,构造圈闭规模和完整性不如库车山前带;成藏模式也体现出分段差异,上白垩统-阿尔塔什组膏泥岩和普司格组泥岩的封闭效果较好,但运移路径复杂,先存油气易遭受后期调整和破坏。塔东南山前带具有一定构造分段性,若羌凹陷山前以冲断变形为主,远离山前的第二排背斜、断背斜圈闭具备基本的成藏条件;民丰凹陷山前以叠瓦逆冲和三角带构造为主,古近系膏泥岩封盖能力有限,深部逆冲断块及凹陷内部的低幅度背斜等是较现实的勘探目标。

Controlling of differential deformation on hydrocarbon accumulation of primary piedmonts in the Tarim basin

Tectonic deformation and activity intensity of the range-frontal fold-thrust belts differ much in the Kuqa area, and southwest and southeast Tarim Basin, which determines imbalances in the geologic conditions for hydrocarbon accumulation and distribution. Combined with analysis of typical accumulation patterns, we analyze the features of such differential deformation and its controlling on hydrocarbon accumulation by comparative research on seismic sections of these three structural belts. The Kuqa mountain front is dominated by thrust faults and salt structure, where structural traps are of large-scale and high amplitude. There are two kinds of hydrocarbon accumulation mode: over-salt and under-salt with source rock-rooted faults developed in the Kuqa fold-thrust belt and salt layers in the Kumugeliemu formation which are favorable for the hydrocarbon preservation. The southwestern Tarim exhibits obvious structural segmentation along the strike with triangle zones, duplex structures and superimposed anticlinal folds. Scale and integrity of structural traps in this region are inferior to the Kuqa fold-thrust belt. Hydrocarbon accumulation mode of the southwest Tarim is also characterized by segmentation difference, which is sealed by two good-quality layers of detachments including lower Cretaceous-Aertashi Formation gypsum-mudstones and Pusige Formation mudstone, whereas the oil-gas migration path is relatively complex and pre-existing oil-gas is vulnerable to be modified by tectonic movement in the later period. The southeast Tarim basin has a certain segmentation feature with intense thrust deformation in the Ruoqiang piedmont zone, where the second anticline and faulted anticline belts have the basic conditions for hydrocarbon accumulation. The Minfeng range-frontal depression is a triangle zone with imbricate thrusts, which is sealed by Paleogene gypsum-mudstones to a limited degree, where the deep fault blocks and low-amplitude anticlines are probably favorable exploration targets.