One of the challenges in evaluating and estimating the gas storage and migration of coal has been the investigation of complex pore structures, especially in the nanoscale. The present study provides new insights into nanoscale pore types, and the genesis, classification, and structure characteristics of high-rank coal by investigating 10 anthracite coals in the Shanxi Formation and Taiyuan Formation of the Xinjing Coal Mine in the Qinshui Basin, North China. A series of experiments that combined the qualitative observation method of argon ion polishing technology in combination with field emission-scanning electron microscope and quantitative analysis methods of low-pressure N ₂ gas adsorption and mercury intrusion porosimetry were performed to characterize nanoscale pore structures and its influence on gas behavior. The results revealed that various types of nanoscale pores exist in the coal matrix. Descriptive classifications for nanoscale pores consist of three major groups (organic matter pores, mineral-related pores, and micro-fractures), and nine subtypes was summarized to correlate pores to the networks. Furthermore, mercury intrusion porosimetry, low-pressure N ₂ gas adsorption, and image processing were combined to determine the pore size distributions, indicating that pore sizes are bimodally distributed with two broad peaks. The major peak at approximately 20–400 nm was mostly associated with isolated microscopic organic constituents interparticle nanopores, while a minor but prominent peak at the macro-pore to micro-fracture scale was more associated with epigenetic pores, mineral-related pores, and micro-fractures. Furthermore, image processing also provides a specialized approach to reveal the structure and diameter of different types of nanoscale pores. The combination of quantitative test and qualitative observation indicate that different major pore types dominate each size range of reservoir space in coal. These results lead to a feasible assumption that the poor connectivity of nanoscale pores and lack of seepage channels between the nanoscale pores and fracture-cleat networks may have led to the low “micro-permeability” of the coal matrix, which affects the productivity of coalbed methane in high-rank coal.

The influence of high-rank coal’s pore characteristics on the physical properties, gas-bearing properties, and exploitation of coal reservoirs is becoming more and more prominent. How to establish the classification to describe the pore networks combining quantitative and qualitative characteristics has emerged as a major problem, which may offer a scientific foundation to deepen the understanding of this issue. In this research, the structure and fractal characteristics of reservoir pores were determined after analyzing 20 high-rank coal samples from Xinjing Coal Mine in the Qinshui Basin with the application of the high-pressure mercury intrusion method (HPMI) and argon ion polishing–field emission scanning electron microscopy (AIP–FESEM). The results show that the tested coal samples were bipolar distributed, with transitional pores and micropores dominating the pore volume, followed by macropores. The Menger sponge fractal models manifested two or three distinct straight-line segments with demarcation points of 65 nm and 1000 nm. A natural classification with three major pore types of diffusion pores (D-pores), seepage pores (S-pores), and pico pores (P-pores), demarcated by pore size intervals of 65 nm and 1 nm and seven sub-types, was established to relate pores to pore networks based on these fractal characteristics and the kinetic characteristics of methane molecules. This classification scheme can characterize the relationship between pore types and the corresponding major occurrence and transport mechanisms of the gas. In addition, P-pores and D-pores are predominately nanoscale OM pores with three major genetic types of organic constituent interparticle pores (5–200 nm), metamorphic pores (<5 nm), and intermorphic pores (65 nm). Since fractal analysis is a more comprehensive characterization of reservoir structure and quantitatively reflects the pore structure, undulating state, and roughness of the inner surface, fractal parameters can be used as an important index to describe the pore structure characteristics of high-rank coal reservoirs.

Cultural relics and historical sites serve as carriers of cultural, historical, and artistic information. However, any damage incurred by these cultural relics can result in the loss of information, consequently impacting sustainable conservation and revitalization of the cultural heritage. Han Dynasty stone reliefs are a representative carrier of art and history during the Han Dynasty, an early stage of Chinese history. Due to the influence of materials, carving techniques, and protective measures, the conservation and revitalization of Han Dynasty stone reliefs have been significantly restricted. In this study, a systematic investigation was carried out to study the current situation and existing problems related to the protection of Han Dynasty stone reliefs. Additionally, a case study was conducted using the Wuling Ancestral Hall (Wuliang Shrine) as an example, to explore the integration of 3D digital technology as a new sustainable approach. The results show that natural weathering and conventional techniques have caused irreversible information loss. Thus, adopting a three-dimensional digital perspective is crucial when considering the information preservation and revitalization of Han Dynasty stone reliefs. To achieve this, 3D digital models of representative stone reliefs, tomb chambers, and other sculptures from the Wuliang Ancestral Hall were established. These models provide new paths for accurately recording 3D information and better utilizing cultural heritage. Faced with the challenge of preserving historical heritage and its associated information, a workflow including 3D scanning, data collection and processing, 3D modeling, visualization, and information utilization is proposed. This approach offers new approaches for sustainable conservation and revitalization of Han Dynasty stone reliefs.

Transitional upper carboniferous Shanxi Formation coal-bearing strata in Qinshui Basin have been proven to be a set of mixed unconventional gas-bearing reservoirs forming a multi-superimposed gas system that consists of multiple independent fluid pressure systems vertically through the strata. An experimental protocol was designed to compare the pore networks in high-rank coal, shale, and tight sandstone reservoirs from Shanxi Formation using quantitative and qualitative experimental methods, including high-pressure mercury injection porosimetry (MIP), low-pressure nitrogen gas adsorption (LN₂GA), and argon ion polishing–field emission scanning electron microscope (AIP-FESEM). The results show that genetic and structural differences in pore types, morphology, abundance, and proportion in coal, shale, and tight sandstone reservoirs are significant, reflecting strong heterogeneity characteristics. Pore networks determine the roles of different types of reservoirs in gas-bearing systems through differentiated pore structure, development degree, and spatial distribution. Due to the differences in nanopore development and connectivity, coal and tight sandstone reservoirs provide important reservoir spaces for adsorbed and free gas in the system. Thus, they become influential factors controlling the relationship between the gas-bearing subsystems with different fluid pressures. The lack of mesopores in shale and relatively weaker heterogeneity between layers lead to the phenomenon that continuously developed shales of a specific thickness are more likely to be the interlayers that divide the superimposed gas-bearing system. Systematic comparison of pore development characteristics will provide scientific support to further explain the formation mechanism of multi-superimposed gas systems in coal-bearing strata from the perspective of pore networks and provide guidance for the development of unconventional natural gas in coal-bearing strata.

The pore structure and fractal characteristics of the Lower Cambrian marine organic-rich shale in the southern China were comprehensively studied using low- pressure N2 adsorption and organic geoch...

Using the tight sandstone of the lower Permian Shanxi Formation in the southern Qinshui Basin as an example, we have developed the concept of “geomechanical sweet spots” in a strongly deformed strike-slip fault zone. The evaluation elements for geomechanical sweet spots include current tectonics, paleotectonics, fractures, and rock brittleness. The high-angle basement-surface strike-slip faults that developed in the study area control the formation and development of the descending plane (upper plate) positive traction folds and the ascending plane (lower plate) isopach folds. The current tectonics and the paleotectonics in the mid-Himalayan tectonic period have a certain adjustment effect on the distribution of natural gas. We predicted the fracture development area of the target layer in the main episode of the Himalayan period based on the 3D finite-element method. The regions with a higher fracture development degree are mainly distributed in the Sitou-Houchengyao strike-slip fault zone and the northwestern and eastern parts of the study area. We also divide the brittleness index of sand group II into four grades. Based on a single-factor evaluation of the current tectonics, paleotectonics, fractures, and rock brittleness, we established a standard parameter system for evaluating the geomechanical sweet spots of tight gas sandstone reservoirs.