阿尔金山前带东坪—牛中地区新生代构造解析及其油气意义

Tectonic analysis and petroleum significance of Cenozoic faults in Dongping-Niuzhong area in Altyn piedmont

利用高精度三维地震数据,对柴达木盆地阿尔金山前带东坪牛中地区新生代北西南东向和近东西向两组断裂构造演化过程及其油气意义进行研究。牛中地区北西南东向断裂发育于渐新世,渐新世至中新世在东坪、牛中地区发育一系列压扭断裂相关褶皱;中新世之后,随着阿尔金走滑断裂带的持续扩展,阿尔金山前带近东西向断裂开始大规模发育,近东西向断裂的活动及牛中北部基岩的大规模隆起承受了牛中地区的大部分压扭分量,导致牛中地区北西南东向断裂于中新世后活动明显减弱。继承性的侏罗系凹陷中发育了良好的烃源岩,断裂是东坪、牛中地区油气运移的有效通道,油气充注时间与北西南东向断裂及其相关构造形成时期匹配较好,断裂相关背斜成为油气聚集的有利目标;其中,牛中地区中新世以来受新生代构造影响较小,有利于气藏保存。

The evolution process and petroleum significance of two groups of fault structures,the NW-SE trending and near EW trending ones in the Cenozoic of Dongping-Niuzhong area of the Altyn piedmont,Qaidam Basin,were investigated using high precision 3-D seismic data.The NW-SE faults were generated in Oligocene,causing the formation of a series of folds related to transpression faults in the Niuzhong and Dongping area.After the Miocene,with the continuous extension of the Altyn Tagh strike-slip fault zone,the EW trending faults began to develop massively in Altyn piedmont.The activity of near EW trending faults and large-scale uplift of the bedrock in the northern Niuzhong area shared most of the compression torsion in Niuzhong and Dongping area,consequently,the activity of NW-SE trending faults weakened significantly after the Miocene.Then good hydrocarbon source rocks developed in the inherited Jurassic sags.The faults were effective pathways for oil and gas migration in Dongping and Niuzhong areas,and the oil and gas charging time matched well with the formation period of the NW-SE trending faults and their related structures,making the fault-related anticlines favorable targets for oil and gas accumulation.The Niuzhong area has been less affected by the Cenozoic movement after the Miocene,and thus has better conditions for gas reservoir preservation.