Types of biogenic quartz and its coupling storage mechanism in organic-rich shales: A case study of the Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation in the Sichuan Basin, SW China

GUAN Quanzhong,DONG Dazhong,ZHANG Hualing,SUN Shasha,ZHANG Surong,GUO Wen

Fig. 9. Effect of biogenic quartz on the Wufeng-Longmaxi Formation reservoir space in Well W202 of Weiyuan gas field. (a) 2 570.97 m, siliceous shale, organic pores (red dotted line) contain type II authigenic quartz, which effectively supports the development of pores, helium ion scanning electron microscope photo; (b) 2 569.46-2 569.49 m, micro-cracks (red dotted line) in the shale, XRF large thin-section assembly image; (c) 2 569.46-2 569.49 m, Si element distribution corresponding to figure b, showing overall uniform distribution of Si, more calcium filling micro-cracks in the middle and bottom, forming a relative low silica content "artifact".