莺歌海盆地新构造运动与超压体系喷溢油气成藏作用
NEOTECTONICS AND THE ACCUMULATION OF OIL AND GAS ATTRIBUTED TO THE EXPULSION ACTIVITY OF GEOPRESSURED SYSTEM IN THE YINGGEHAI BASIN
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摘要: 莺歌海盆地是在岩石圈伸展减薄和红河断裂带南段的右旋扭动联合作用下形成的一个以伸展为主的转换-伸展盆地。受该应力场作用,盆地新构造运动活跃,主要表现包括中新统末、上新统与第四纪之间及层系内部的不整合,盆地的沉降,沉积中心的迁移,断裂活动,底辟带的发育与分布,泥火山和地震等。新构造运动不但控制了盆地的形成演化、沉降-沉积中心的迁移和底辟构造带发育以及它们的雁行排列特征,同时还控制了盆地油气的成藏和分布。莺歌海盆地是一个强超压盆地,新构造时期断裂的多期活动及其控制的多期底辟活动不但形成超压体系(包括油气)快速垂向运移的通道,同时决定了莺歌海超压盆地油气田的快速幕式充注成藏规律。成熟的烃类以溶解状态储存在超压体系中,当超压体系孔隙流体压力大于封闭盖层破坏压力时封闭盖层就产生水压破裂,超压体系便沿着活动断裂和底辟带等通道发生喷溢活动,油气向上或侧向往过渡带和常压带运移聚集成藏,随着压力的下降,断裂重新闭合形成新的封闭层。这一喷溢过程以幕式活动形式周而复始,在超压盆地的过渡带和常压带中形成大的油气藏。Abstract: The Yinggehai basin is a transform-extension basin that is dominated by the extension and formed by the combination function of the extension and thinning of lithosphere and the right-lateral movement of the Red River Fault in the basin. Under this tectonic stress,the neotectonic movement of the basin is active. The main manifestations of the neotectonics include the formation of unconformities at the end of the Miocene,the Pliocene and Quaternary within the sequences,the shift of sedimentation centers,the strong fault activities,echelon pattern of diapir structures,mud volcanoes and earthquakes. The neotectonic movement in the Yinggehai basin not only controlled the formation and evolution of the basin,the shifting of subsidence and sedimentation centers and the formation of diapir structure belts and their echelon arrangement,but also dominated the petroleum accumulation and distribution. The Yinggehai basin is a strong geopressured basin,the multiphasic fault activities and the multiphasic diapirism dominated by the fault activity in the neotectonic age formed the transport passage system for the geopressured system and petroleum,and induced the episodic expulsion and accumulation of oil and gas. The geopressured system containing the mature hydrocarbon emitted along active fault and diapir structure as the liquid pressure of geopressured system exceeded the rupture strength of the sealed layer of the geopressured system,the oil and gas generally accumulated in the transition zone of pressure and normal pressure zone with upward and lateral geopressured fluid release,and then the fault closed with the pressure of geopressured fluid descending. This expulsion process of geopressured system is episodic and generally forms big oil field or gas field in the transition zone of pressure and normal pressure zone in geopressured basin.