Buried structures in the Wuwei Basin, northeast margin of the Qilianshan structural belt
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摘要:
祁连山东北缘武威盆地是阿拉善地块南缘主要的含油气盆地，也是石炭系页岩气勘探的热点区域。长期以来，由于武威盆地为第四系覆盖，盆地的结构和构造存在很大争议。通过地震剖面探测和钻探地层分析，对武威盆地西部的结构和构造进行了厘定。地震剖面和钻探揭示，研究区前寒武纪基底之上主要发育下部寒武系、中部新近系和上部第四系3套构造层。下构造层构造复杂，发育下寒武统(大黄山组)断陷盆地、下寒武统冲断-褶皱带和下白垩统断陷盆地。下构造层的构造分析，结合区域地层和构造特征，提出武威盆地经历了早寒武世NE—SW向伸展变形、侏罗纪末—白垩纪初NE—SW向地壳缩短变形及早白垩世NE—SW向伸展变形3期构造演化过程。武威盆地东、西部的地层序列和构造差异表明，武威盆地以武威-蔡旗构造隆起带为界，可划分为东、西2个构造单元。
Abstract:The Wuwei Basin in the northeast margin of Qilianshan structural belt is one of the oil/gas-bearing basins for Carboniferous shale gas exploration in the west China. However, much disagreement is going on the structures and tectonics in the Wuwei Basin due to the Quaternary covering of the basin. Here we conducted the 2D seismic surveying and drill exploration, and defined three sets of structural layers from the seismic profile, e.g., lower structural layer composed of Lower Cambrian strata (Dahuangshan Formation) and Early Cretaceous strata, middle structural layer consisting of Neogene strata, and upper structural layer formed of Quaternary strata. In the lower structural layer, some faulted basins developed, which were filled by the Lower Cambrian or Late Cretaceous; and the Lower Cambrian was also thrusted and folded.Together with regional structure analysis, we suggest three stages of deformation process, including NE-SW extension in the Early Cambrian, NE-SW shortening in the Late Jurassic-Early Cretaceous, and NE-SW extension in the Early Cretaceous.In addition, it also shows the differences on the regional structure and sedimentary sequences in the west and east parts of the Wuwei Basin, which indicates the Wuwei Basin, limited by the Wuwei-Caiqi structural belt, can be divided into west and east sub-basins.
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表 1 可控震源地震试验方案
Table 1. Experimental plan of vibrator seismic
序号 项目 因素 备注 工作量统计 1 振动次数 1次 固定因素
1台20 s；6~84 Hz
70%2*3炮=6炮 2次 3次 2 扫描长度 14 s 固定因素
1台1次；6~84 Hz
70%2*8炮=16炮 16 s 18 s 20 s 22 s 24 s 26 s 28 s 3 震源出力 55% 固定因素
1台1次；6~84 Hz
20 s2*5炮=10炮 60% 65% 70% 75% 4 扫描频率 6~76 Hz 固定因素
1台1次20 s
70%2*9炮=18炮 6~84 Hz 6~96 Hz 8~76 Hz 8~84 Hz 8~96 Hz 10~76 Hz 10~84 Hz 10~96 Hz 
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表 2 二维地震测线观测系统参数
Table 2. Parameters of 2D seismic observation
项目 参数 观测系统 3L1S 排列方式 单排列300道固定接收 覆盖次数 200次 接收道数 300道×3=900道 道距 20 m 炮点距 20 m 接收线距 20 m
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