川东石炭系天然气成藏的地球化学模式

GEOCHEMICAL MODE OF GAS RESERVOIR FORMATION IN CARBONIFEROUS IN EAST SICHUAN

本文根据含油气系统理论 ,采用气藏地球化学方法 ,研究了四川盆地东部石炭系天然气成藏的地球化学模式。应用储层沥青中的芳香烃馏份进行了川东石炭系与志留系和下二叠统碳质页岩的特征对比 ,证实了石炭系的储层沥青与下志留统亲缘关系密切。石炭系地层水和储集岩经历了沉积、暴露剥蚀和深埋藏三个演化时期 ,天然气主要经历了大致相同的两次成藏过程 ,印支—燕山期为古油藏的主要成藏期 ,喜山期为天然气的主要成藏期。应用天然气地球化学特征探索了石炭系天然气的运移方向 ,提出了川东地区注入时间较早的气藏有大池干井、高峰场、相国寺和大天池等 ,其他气藏相对较晚 ,其中大池干井构造天然气的注入顺序依次为万顺场、吊钟坝、龙头和磨盘场。目前研究表明 ,石炭系天然气存在 3个运移方向 ,即开江古隆起西部由南西向北东和由西向东两个方向 ,开江古隆起东南部则可能有石柱复向斜方向运移来的天然气。指出石炭系天然气的聚集受开江印支—燕山期古隆起的控制 ,喜山运动形成的圈闭对天然气成藏具有调整作用 ,从气藏地球化学角度提出了下步勘探较为有利的区块 。

On the basis of the theory of petroleum system,t he geochemical mode of gas reservoir formation in Carboniferous in East Sichuan Basin was studied by applying gas reservoir geochemical methods.Through contrast ing the aromatic hydrocarbon fraction of reservoir bitumen in carboniferous wit h the carbonaceous shales in Silurian and Lower Permian in East Sichuan,it was p roved that the reservoir bitumen in Carboniferous is of a strong affinity with L ower Silurian.The Carboniferous formation water and reservoir rocks suffered thr ee evolution stages,i.e. sedimentation,denudation and deep burial stages and the gas reservoir formation was suffered roughly the same two stages,i.e Indo Chin e se～Yanshan epoch was the main formation stage of ancient oil reservoirs and Him alayan epoch was that of gas reservoirs.In the paper,according to natural gas ge ochemical characteristics,the gas migration direction is discussed and it is pro posed that the gas reservoirs with an early charging time are in the Dachiganjin g,Gaofengchang,Xiangguosi and Datianchi structures in East Sichuan,the others be ing relatively later,in which the gas charging sequence in Dachiganjing structur e was the Wanshunchang,Diaozhongba,Longtou and Mopanchang highs successively.Thr ough studying at present it is shown that there were three gas migration directi ons in Carboniferous,i.e. the gas was migrated from southwest to northeast and f rom west to east in the west part of Kaijiang ancient uplift and the gas in the southeast part of the ancient uplift might come from the direction of Shizhu synclinori um.Finally it is pointed out that the gas accumulation Carboniferous was control led by the Indo Chinese～Yanshan epoch Kaijiang ancient uplift;the traps formed during Himalayan epoch played an adjustment role in gas reservoir formation;and the next beneficial exploration tracts are put forward from the point of view of gas reservoir geochemistry,which has a guiding significance for deepening Carbo niferous exploration.