川中地区磨溪气田嘉二段砂屑云岩储集层成因

Jia-2 Member doloarenite reservoir in the Moxi gas field,middle Sichuan Basin

对四川盆地磨溪气田嘉陵江组嘉二段二亚段C层(T1j22C)砂屑云岩宏观与微观特征进行深入分析,建立滩相碳酸盐岩优质储集层的成因模式。原生粒间孔是滩相碳酸盐岩储集层的主要储集空间,其主要特征及判识标志包括:储集层发育严格受沉积微相控制、孔隙以残余粒间孔和溶扩残余粒间孔为主、颗粒接触处仅有海底胶结物发育、初期压实使颗粒呈线-凹凸接触的格架支撑及部分孤立粒间孔隙的埋藏胶结物不具溶蚀现象等。原生粒间孔的保存机制为:在海底胶结后,初期压实使具早期环边胶结物的颗粒呈格架支撑、喉道减小;压实流体胶结使滩体周缘致密化,并且粒间孔内有限的浅埋藏胶结物使喉道堵塞,成岩流体达到溶蚀-胶结平衡后胶结作用终止;后期埋藏溶蚀主要调整、优化改造先期孔隙层,其对单个储渗体储集空间的绝对增加值仅占次要地位,并不改变这类储集层的储渗体时空分布。

Based on analysis on the macroscopic and microcosmic features of doloarenite in C layer,sub-member 2,Jia-2 Member of the Jialingjiang Formation in the Moxi gas field,the genetic mechanism of favorite reservoirs in beach facies carbonate rock is established.Primary inter-granular pores are the main reservoir spaces in the beach facies carbonates,which have the following key characteristics and identification signs： the reservoir development was strictly controlled by the depositional microfacies;the main pore types are residual inter-granular pores and dissolved-enlarged residual inter-granular pores;only submarine cement existed in the grain contact;initial compaction led to grains under framework support in line-concavo-convex contact and the burial cement in some separate inter-granular pores being not dissolved.The conservation mechanism of primary inter-granular pores is described as follows： after submarine cementation,the initial compaction made grains with early rim cement under framework support and the throats decrease accordingly;the compaction fluid cementation compressed the beach body’s margin,the limited shallow burial cementation in inter-granular pores plugged the throats,and the cementation terminated after the diagenetic fluid reached dissolution-cementation balance;late burial-dissolution mainly adjusted and optimized early porous strata,which only played a secondary role in increasing the reservoir space of single permeable reservoir bodies and didn’t change the spatiotemporal distribution of this kind of reservoir.