Characterization of Quartz in Wufeng-Longmaxi Shale: Implications for Sedimentology and Shale Gas Exploration

Abstract

Summary Existing exploration and research about Wufeng—Longmaxi shale gas reservoir show that the content of quartz is generally more than 50% and the American shale gas reservoir also share the same characteristics. The objective of this paper is to further these three question: what is the source of quartz? Why is quartz enriched? How does quartz affect the shale gas reservoir? In this study, the mineralogical analysis was conducted on a total of 202 samples collected from Longmaxi Formation. The samples were used for methane sorption analysis, the XRD, Microscope, SEM, TOC analysis. According to the final results, Wufeng—Longmaxi shale the quartz can be divided into 3 types according to their sources: Biogenic source quartz, terrigenous source quartz, Recrystallization quartz. Different sources of quartz have different effects on shale reservoirs: Biogenic quartz containing an abundance of organic matter and quartz critical to form high quality source rocks and shale reservoirs, Terrigenous quartz impedes organic matter accumulation but makes the rock brittle, Recrystallization of quartz is negative to the physical reservoir properties. Defining quartz sources should be a new key factor for the Exploration and Evaluation of shale gas reservoirs.