川东三叠系飞仙关组碳酸盐岩的阴极发光特征与成岩作用

四川盆地东部三叠系飞仙关组是近年来我国发现的重要天然气储层, 高孔隙度、高渗透率的碳酸盐储层都分布于白云岩地层中, 因而碳酸盐的成岩作用, 尤其是白云岩化作用和白云岩的成因为石油地质学家和沉积学家高度关注.对四川盆地东部罗家寨构造三叠系飞仙关组42个碳酸盐岩样品进行了阴极发光分析, 结合与之有关的Mn、Fe、Mg元素分析和岩石学研究, 讨论了包括白云岩化作用在内的碳酸盐岩成岩过程中可能的成岩流体性质及来源.四川盆地东部三叠系飞仙关组碳酸盐岩普遍具有很弱的阴极发光性, 这与其很低的Mn、Fe含量有关, 说明沉积期后非海相流体对飞仙关组碳酸盐岩的影响非常有限, 海源流体在成岩过程中发挥了主导作用; 不同石灰岩类型和不同白云岩类型仍然具有不同的阴极发光性, 成岩组分含量越高的碳酸盐岩, 或者说与沉积期后流体(主要是孔隙流体) 关系越密切的碳酸盐岩的阴极发光强度越低, 说明随着埋藏成岩作用的进行, 四川盆地东部三叠系碳酸盐岩孔隙流体受海源流体的影响是逐渐增强的; 阴极发光分析结果表明, 作为四川盆地东部主要储集岩的结晶白云岩形成机制与埋藏过程中的深循环流体有关, 这种深循环流体没有或很少穿越铝硅酸盐地层, 但穿越了三叠系内部的某些海相地层, 这些海相地层可能是广泛存在于四川盆地三叠系的蒸发盐地层, 由蒸发盐成岩过程提供的海源流体参与了结晶白云岩的白云岩化作用. 

Cathodoluminescence and Diagenesis of the Carbonate Rocks in Feixianguan Formation of Triassic, Eastern Sichuan Basin of China

The Feixianguan carbonates of Triassic in Eastern Sichuan basin are the most important gas reservoir of China,and the reservoir with higher porosity and permeability is all dolomites,so the diagenesis,specially origin of dolomites is drawing increasing attention of petroleum geologists and sedmentologists. 42 carbonate samples,from Feixianguan Formation,Luojiazhai Gas Field of Eastern Sichuan basin,were studied by cathodoluminoscope. The results,together with the petrology analysis and Mn,Fe,Mg element tests,show that the carbonate rocks in Feixianguan Formation of Triassic,Eastern Sichuan basin of China generally have dull cathodoluminescence,which results from very low Mn and Fe contents,suggesting the limited influence of non-marine fluid during post-sedimentation. The diagenesis of the carbonates should have been governed by some kinds of marine fluid. However,the limestones and dolomites with different structures also display various cathodoluminescent intensities. The carbonates with more diagenetic components luminesce duller,in other words,the carbonates influenced by more post-sedimentary fluids (mainly pore waters) luminesce dull,suggesting the enhancement of marine fluid effect with the process of burial diagenesis. The cathodoluminescence of crystalline dolomite,which is the most important gas reservoir,reflects the deep burial conditions of diagenetic fluids that have not circulated through clastic rocks within the basin,but through some marine beds such as thick evaporates which are widely distributed in the Triassic of Sichuan basin. The dissolution or dehydration of evaporates provided the marine fluid that participated in the dolomitization of crystalline dolomite.