Characteristics of Pore Structure and Gas Content of the Lower Paleozoic Shale from the Upper Yangtze Plate, South China

Abstract

This study is predominantly about the differences in shale pore structure and the controlling factors of shale gas content between Lower Silurian and Lower Cambrian from the upper Yangtze plate, which are of great significance to the occurrence mechanism of shale gas. The field emission scanning electron microscopy combined with Particles (Pores) and Cracks Analysis System software, CO2/N2 adsorption and the high-pressure mercury injection porosimetry, and methane adsorption were used to investigate characteristics of overall shale pore structure and organic matter pore, heterogeneity and gas content of the Lower Paleozoic in southern Sichuan Basin and northern Guizhou province from the upper Yangtze plate. Results show that porosity and the development of organic matter pores of the Lower Silurian are better than that of the Lower Cambrian, and there are four main types of pore, including interparticle pore, intraparticle pore, organic matter pore and micro-fracture. The micropores of the Lower Cambrian shale provide major pore volume and specific surface areas. In the Lower Silurian shale, there are mesopores besides micropores. Fractal dimensions representing pore structure complexity and heterogeneity gradually increase with the increase in pore volume and specific surface areas. There is a significant positive linear relationship between total organic carbon content and micropores volume and specific surface areas of the Lower Paleozoic shale, and the correlation of the Lower Silurian is more obvious than that of the Lower Cambrian. The plane porosity of organic matter increases with the increase in total organic carbon when it is less than 5%. The plane porosity of organic matter pores is positively correlated with clay minerals content and negatively correlated with brittle minerals content. The adsorption gas content of Lower Silurian and Lower Cambrian shale are 1.51–3.86 m3/t (average, 2.31 m3/t) and 0.35–2.38 m3/t (average, 1.36 m3/t). Total organic carbon, clay minerals and porosity are the main controlling factors for the differences in shale gas content between Lower Cambrian and Lower Silurian from the upper Yangtze plate. Probability entropy and organic matter plane porosity of the Lower Silurian are higher than those of Lower Cambrian shale, but form factor and roundness is smaller.

Pore Characteristics and Gas Preservation of the Lower Cambrian Shale in a Strongly Deformed Zone, Northern Chongqing, China

“…As an unconventional natural gas resource, shale gas has been exploited commercially for more than several decades. However, the occurrence and enrichment mechanism of shale gas have still remained unclear since the formation that shale gas plays is very complicated and controlled by a variety of geological and geochemical factors [1][2][3][4][5][6][7][8][9]. In southern China, the Lower Cambrian and Lower Silurian shales are considered to have great potential [10][11][12][13], but currently, only the Lower Silurian shale gas has been exploited commercially [14,15].…”

Characteristics of Micro–Nano-Pores in Shallow Shale Gas Reservoirs and Their Controlling Factors on Gas Content

“…Although these methods have their strengths, limitations exist, such as the potential for high-pressure mercury intrusion to damage samples [10], whereas low-temperature gas adsorption can avoid sample destruction, thereby increasing sample usability [11]. On the other hand, high-resolution imaging techniques employ various microscopic imaging technologies, such as optical microscopy and scanning electron microscopy (SEM), to directly observe the micro-features of shale pores [12][13][14]. These technologies provide intuitive images of pore structures but, due to the extremely small size of shale pores, require very high imaging resolutions [15,16].…”

Microscopic Flow of CO₂ in Complex Pore Structures: A Recent 10-Year Review

“…Mercury intrusion porosimetry (MIP) [44][45][46], scanning electron microscopy (SEM) [47,48], and gas adsorption [49][50][51] have been used to characterize the pore structures of the storage body and further explore the flow of CO2. Du et al [52] used high-pressure mercury intrusion and permeation experiments to investigate the effect of CO2 injected into coal.…”