Influence of reservoir properties on gas occurrence and fractal features of transitional shale from the Linxing area, Ordos Basin, China

Shale gas occurrence is mainly affected by pore heterogeneity caused by material composition. Therefore, transitional shale samples collected from the Taiyuan Formation in the Linxing area were carried out with the low-temperature nitrogen adsorption (LT-N2GA), geochemical composition, and scanning electron microscopy (SEM) observation tests. Surface and structural fractal dimensions (D1 and D2) were obtained by using the Frenkel-Halsey-Hill (FHH) model. Based on this, the influence of pore development characteristics and material composition on pore homogeneity was studied. The maturity of organic matter (OM) is beneficial to the development of pore volume (PV) and specific surface area (SSA), and it increases pore surface roughness and pore structure complexity. The total organic carbon content is negatively associated with PV, SSA, and fractal dimensions. The influence of clay minerals on the fractal dimension is complex. D1 increases with increasing chlorite and illite contents but decreases with increasing kaolinite and illite mixed-layer contents. D2 increases with increasing chlorite, illite, and kaolinite contents and decreases with increasing illite mixed-layer content. Brittle minerals are mainly composed of quartz; an increased quartz content is not conducive to the development of pores, but it increases the homogeneity of pores.