The distribution characteristics of brittle minerals in the Lower Cambrian Niutitang Formation in northern Guizhou

Abstract: To explore the influence of brittle mineral composition and morphological characteristics within the shale matrix on the generation of complex fractures and reservoir reconstruction, the microstructure and fractal characteristics of minerals within the shale matrix of the Lower Cambrian Niutitang formation in northern Guizhou were investigated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectrometer (SEM-EDS), and micro-computed tomography (Micro-CT). Based on image processing technology and digital core modelling, a three-dimensional shale digital core model was established. The distribution and morphological characteristics of brittle minerals within the shale matrix were studied from the fractal perspective. The model for evaluating the mineral particles and pores within the shale matrix was established. The results show that the siliceous mineral composition is high, and it is mainly derived from the interaction of continental detrital quartz particles and biogenetic effects; the density of the brittle minerals is greater than other mineral components mainly distributed in the range of equivalent diameters of 200 – 800 μm; the distribution complexity of the brittle minerals was quantitatively analysed from the fractal perspective; the fractal dimension partly reflects the generating ability of complex fractures; the distribution angle and complexity of brittle mineral particles within the shale matrix partly determine the fracture morphology characteristics. The physical properties of shale reservoirs were studied from three aspects: complex fracture generation ability, pore connectivity and heterogeneity, and the evaluation model of mineral particles and pores was established using the value of fractal dimension, ratio of organic matter pores, tortuosity of pores, relative deviation of pore size distribution, and relative deviation of specific surface area. The model provides a basis for further study on the relationship between reservoir reconstruction potential and physical properties of shale reservoirs.