Abstract
Organic-rich marine shale in South China has great potential for gas generation, and the pore structure has a considerable influence on the enrichment of shale gas. The nanoscale pore characteristics and fractal characteristics of the Niutitang shales in the Fenggang block were studied by means of methane adsorption and low-pressure nitrogen adsorption experiments, porosity and permeability tests, X-ray diffraction analyses, organic geochemical analyses, and field emission scanning electron microscopy. The fractal geometry of the pore structure was assessed, and the factors influencing the pore structure were determined. We used a fractal Frenkel–Halsey–Hill-based method to obtain the fractal dimensions D1 and D2 by nitrogen adsorption at relative pressures of 0–0.5 and 0.5–1, respectively. The relationships between the shale pore structure parameters and the fractal dimensions, the mineral composition, the total organic carbon content, and the pore structure parameters of shale are discussed. In addition, the significance of D1 and D2 and the implications of the fractal dimension for the adsorption capacity of shale are investigated. The results show that the two fractal dimensions are positively correlated with total organic carbon content and specific surface area, negatively correlated with quartz content and average pore diameter, but have a weak relationship with clay mineral content and total pore volume. The Niutitang shale samples are dominated by mesopores, and the pore structure is complicated. The results presented here indicate that fractal analyses represent an effective method of characterizing the complexity of pore structure.
Highlights
Global energy shortages have led to an increased interest in shale gas (Gasparik et al, 2012)
Previous studies on the fractal characteristics of coal show that the fractal dimension D1 reflects the fractal dimension of the surface and that the fractal dimension D2 represents the fractal dimension of the pore structure (Yao et al, 2008)
These results deviate from the definition of the fractal dimension of the pore structure and the pore surface
Summary
Global energy shortages have led to an increased interest in shale gas (Gasparik et al, 2012). A new type of unconventional energy, has effectively alleviated the pressure of global supply and demand of oil and gas resources, especially in North America, where exploration and development of shale gas has made outstanding advances. Exploration efforts related to this new form of energy have increased around the world. The Fenggang block study area is located in northern Guizhou Province (Figure 1). The structural location of the study area is in the trough fold zone of the southeastern margin of the upper Yangtze plate in Western Hubei–Hunan Province, where the stress fields and structural conditions are complicated because of multistage tectonic activity and deformation. The Niutitang black shale in the Fenggang block has a thickness of 40–70 m and good continuity, which are beneficial to the accumulation of shale gas
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