Mechanism of fault controlling shallow layer natural gas migration and accumulation in the southern Daqing Placanticline
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摘要: 大庆长垣南部包括葡北、敖包塔和葡两3个局部构造.黑帝庙油层的形成与3种不同演化历史断层有关：反转期断裂（Ⅲ犁）、断陷期形成坳陷期和反转期均活动的断裂（Ⅰ-Ⅱ-Ⅲ型）和坳陷期形成反转期活动的断裂（Ⅱ-Ⅲ型）；其中连通气源岩且活动期与大量生排气期相匹配的Ⅰ-Ⅱ-Ⅲ型和Ⅱ-Ⅲ型断裂是生物气垂向运移的主要通道，Ⅰ-Ⅱ-Ⅲ型断裂是深部CO2向上运移的主要通道.这些断层均是“似花状”断层组合的边界断层，对倾边界断层控制背斜和鼻状构造形成.数值模拟表明：对倾的气源断层与地层产状的配置关系共同控制天然气运移方向和聚集的部位，由于葡萄花和敖包塔构造西缓东陡，因此天然气主要富集在背斜东翼和背斜之间的断块上.Abstract: The southern Daqing Placanticline consisted of three local structures, namely, the Pubei, Aobaota and Puxi Structures.The Heidimiao reservoir related to three different evolutional faults:the inversed faults (type Ⅲ), faults forming in fault-depressing and active in depression and inversion periods (type Ⅰ-Ⅱ-Ⅲ),faults forming in depressing and active in inversion period (type Ⅱ-Ⅲ).Among them, the faults of types Ⅰ-Ⅱ-Ⅲ and Ⅱ-Ⅲ, which connected gas source rock and matched the period of plenty of gas discharge,were main vertical pathways for biogas, and the faults of type Ⅰ-Ⅱ-Ⅲ were main pathways along which deep CO2 migrated up-wards.These faults were boundary ones,with a "flower-like" combination.The anticlines and nose structures were controlled by opposite-dipping faults.The numerical simulation revealed that the allocation relationship of opposite-dipping faults of gas source and attitude of stratum controlled the direction of gas migration and location of accumulation.The Putaohua and Aobaota Structures were gentle in the west slope and steep in the east slope, so the gas mainly accumulated in the eastern limb of anticline and fault blocks between anticlines.The mudstone of Heidimiao reservoir developed well, which determined the lateral sealing of faults.The lateral sealing ability of faults was quantificated by SGR parameter, which demonstrated the lateral sealing ability being different from trap to trap.
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