Characteristics Study of Reservoirs Pores and Mineral Compositions for Black Shale, Northern Guizhou, by Using SEM and X-ray EDS

Shale reservoir research has become a focus in the study of shale gas, and the special structure feature of shale development at the nano/micro level pore size. Guizhou is one of the shale gas test pilot areas in our country. The northern region under the lower Cambrian Niutitang group hosts more than 100 m of black rock series. The nano/micron level pore in rocks and minerals is a typical structure for black shale in northern Guizhou. According to the limitation of resolution and magnification, the pore types in the shale reservoir cannot be observed using the traditional optical microscope. Nuclear magnetic resonance instruments can accurately study shale reservoir porosity, but cannot obtain the pore morphology and distribution of information. By combining the advantages of Scanning Electron Microscopy (SEM) and X-ray Spectrometry microanalysis, Hitachi S-4800 type of field emission SEM and Energy Spectrometer of Oxford IE250X Max50 to study mineral distribution, morphological characteristics and element composition in the black shale reservoir, a new study was conducted and is reported in this paper. Results indicate that micro fracture and nano/micro level intragranular dissolved pore were found in black shale using field emission SEM. Through the X-ray Energy Spectrum, minerals in black shale are mainly illite and quartz, albite, followed by chlorite, white mica, dolomite, to name a few. The black shale fracture diameter is 0.1-20 μm, which is mainly distributed in 1-5 μm, which is greater than the methane molecule diameter (0.414 nm). Thus, it can be used as a gas migration channel and storage space. In addition, through the X-ray Spectrometer study on the brittleness mineral analysis in quartz, calcite, dolomite and illite, the brittle mineral content of quartz contains 9.1%-78%, and the clay mineral content of illite is 17.6%-25.5%. Therefore, the black shale has high brittleness, making it prone to cracking. The study can provide the basis for reservoir evaluation and prediction of Northern Guizhou.