Genesis of Morphologically Distinct Quartz in Shale and Implications for Reservoir Pore and Fracture Systems: A Review

Quartz, as the predominant mineral in shale, exerts a crucial influence on the development and distribution of reservoir pores and fractures, thereby facilitating the storage and migration of shale gas. In this study, quartz was employed as an indicator mineral to establish relationships among quartz morphology, genesis classification, diagenetic environment, and pore and fracture structure in shale reservoirs. The results demonstrate that shale deposition, diagenesis, and subsequent geological modifications significantly impact the formation and shaping of quartz morphology. The high stability of quartz ensure that its morphological characteristics are well-preserved, providing a reliable basis for elucidating the provenance and depositional environment of shale sediments. Based on the sources of silica and different genesis mechanisms, quartz in shale is primarily categorized into detrital quartz and authigenic quartz. Both types tend to reduce the porosity of shale reservoirs. However, during the formation of authigenic quartz, the organic matter associated with intrabasinal biogenic silica may undergo thermal decomposition, generating abundant secondary organic pores. As a result, the content of secondary biogenic quartz often exhibits a positive correlation with reservoir porosity. Therefore, clarifying the relationships between different quartz morphologies and shale porosity, fractures, and pore and fracture structure is of significant importance.