塔西南坳陷甫沙构造带正反转构造及其石油地质意义

Positive Inversion Structure in Fusha Structure Zone of Southwest Depression of Tarim Basin and Its Significance to Petroleum Geology

塔西南坳陷甫沙构造带褶皱冲断强烈,古近系膏泥岩下层构造变形复杂,具有正反转构造变形特征。侏罗纪—白垩纪区域伸展环境发育大量正断层,后期在喜马拉雅运动中受挤压反转。南部发育高角度基底卷入正反转断层,中部发育叠瓦式逆冲断层,北部边缘变形微弱。相应地将甫沙构造带划分为反转断隆背斜带、楔状叠瓦构造带和逆冲前缘构造带;反转程度南强北弱、西强东弱。对区域构造变形环境的分析表明,西昆仑山隆升引发水平挤压叠加垂直向上的剪切作用,使先存高角度正断层容易被迁就利用进而发生正反转。对正反转相关构造圈闭评价认为:反转断隆背斜带发育的圈闭规模大,幅度低,埋藏浅,落实程度高,但上覆膏泥岩层薄,被断层破坏强烈,油气散失严重;楔状叠瓦构造带发育的圈闭规模小,幅度大,埋藏深,落实程度低,上覆膏泥岩层厚,有利于油气保存;逆冲前缘构造带发育低幅度隆起和地层岩性圈闭。

Intensive fold-thrust deformation is developed in Fusha structure zone of southwest depression of the Tarim basin. The structural deformation of gypsum-mudstone in Paleocene is more intensive and has the features of positive inversion structure. Lots of normal faults, formed in early extensive environment of Jurassic-Cretaceous, were compressed and inverted in Himalayan movement. Positive inversion faults at high angle were developed in the south. Imbricate thrust faults were developed in the center. Deformation is rather weakly in the northern frontier. Accordingly, Fusha structure zone can be divided into three belts, including inverted fault uplift anticline belt, wedge-like imbricate belt and thrust frontier belt. The inversion deformation is more intensive in western and southern part of Fusha structure zone than in the east and north. By analyzing the environmental evolution of regional structure, horizontal compression and vertical shear generated in western Kunlun~ s fold-uplifting, make the pre-existing normal faults easier to invert. By evaluating structural traps formed in positive inversion, it is considered that, in inverted fault uplift anticline belt, the large scale, low relief, shallowly buried and highly confirmed traps with thin superposition gypsum-mudstone layerswere developed, and they were seriously destroyed by thrust faults. Oil and gas dissipated easily. In wedge-like imbricate belt, the small scale, high relief, deeply buried and lowly confirmed traps with thick superposition gypsum-mudstone layers were developed, which is favorable for preservation of oil and gas. Lower relief and formation lithological trap were developed in thrust frontier belt.