WANG Yu1,2, JIN Chan1,2, JIANG Zheng1,2, WANG Li-hua1,2, WANG Jian-qiang1,2, WANG Yan-fei3, PU Jie1,2
(1. Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China;
2. Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China;
3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China)
Abstract: Mineral composition and microcopic pore characteristics are significant for shale gas accumulation and exploration. Organic rich shale samples of Wufeng-Longmaxi formation from Shizhu County (Eastern Chongqing City, Sichan Basin) were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with Ar-ion milling technique. The XRD indicates that main mineral components of Wufeng-longmaxi shale are quartz, feldspar, calcite, dolomite, pyrite, illite, illite/smectite mixed layer and chlorite. Brittle mineral content higher than 50% is favorable for fracturing and the assemblages of clay mineral indicate an idea stratum for shale gas accumulation and exploration. SEM observations suggest that there are three microscopic pore types in Wufeng-Longmaxi shale, including mineral matrix pores, micro fractures and organic matter pores. Mineral matrix pores of hundreds of nanometers to several microns are composed of interparticle pores, intercrystalline pores within pyrite, pores between clay platelets and dissolution pores; micro fractures containing tectonic fracture and foliation crack usually develop along mechanical unstable area with length to a few micrometers and width to hundreds of nanometers; most organic matter are porous and organic matter pores of 30－200 nm are recognized with good connectivity. Generally, dissolution pore is the main pore type developing in Wufeng formation while interparticle pore and organic matter pore are most widespread in Longmaxi formation.
Keywords: Wufeng-Longmaxi formation shale; Chongqing; Sichuan Basin; microscopic pore structures; Ar-ion milling/SEM
ACTA MINERALOGICA SINICA Vol. 36, No. 4, 2016, Page 555-562
