川南地区五峰组-龙马溪组页岩中成岩矿物的种类及其对储层的影响

Impact of different diagenetic minerals on shale reservoirs in Wufeng-Longmaxi Formation in southern Sichuan Basin

页岩成岩作用及其对储层演化的影响一直以来都是页岩气勘探研究的重点,但对多矿物的类型、协同演化方式、以及对储层演化的影响的研究至今薄弱,无法更大限度地评价页岩的优质储层。运用大视域拼接扫描电镜和矿物定量分析2种方法,对四川盆地五峰组-龙马溪组页岩中的成岩矿物进行有效地识别,分析成岩作用对页岩储层发育的影响。基于矿物孔隙的发育程度将黏土矿物、草莓状黄铁矿定义为具多孔特性矿物,石英、长石、自形晶黄铁矿、碳酸盐矿物定义为不具多孔特性矿物,同时建立五峰组-龙马溪组矿物成岩演化序列,并以此探讨成岩作用中优质储层的形成机理:早—中期成岩作用阶段,不具多孔特性矿物形成脆性格架,抑制压实并保持内部孔隙;中—晚期成岩作用阶段,具多孔特性矿物和有机质形成有机复合体,催化有机孔形成。这2类矿物阶段性的贡献共同构建了页岩的优质储层,为研究页岩矿物成岩演化对储层的影响提供了进一步的认识。

The diagenesis of shale and its impact on the evolution of reservoirs has long been a key issue in the exploration of shale gas,but scant research on the types of minerals,their modes of co-evolution,and their impact on the evolution of reservoirs makes it difficult to evaluate high-quality shale reservoirs.In this paper,we use large-field splicing scanning electron microscopy and the quantitative analysis of minerals to identify diagenetic minerals in the Wufeng-Longmaxi Formation shale in the Sichuan Basin,and analyze the impact of their diagenesis on the development of shale reservoirs.We used the degree of development of the pores of minerals to divide them into minerals with and without porous media.We then established a sequence of the diagenetic evolution of minerals in the Wufeng-Longmaxi Formation and discussed the mechanism of formation of the high-quality reservoir.The results showed that minerals without pores formed a brittle framework in the early to the middle diagenetic stages that inhibited compaction and helped maintain the internal pores.The porous minerals and organic matter formed organic complexes in the middle to late diagenetic stages that catalyzed the formation of organic pores.The phased contributions of these two kinds of minerals led to the formation of a high-quality shale reservoir.This provides a sound understanding for examining the influence of the diagenetic evolution of shale minerals on the resulting reservoir.