Characterizing nanoscale pores and its structure in coal: Experimental investigation

Abstract

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

Adsorption Mechanisms of High-Pressure Methane and Carbon Dioxide on Coals

“…The coal pores differ widely in pore size and pore shape and can be categorized into the matrix pore and cleat pore. − The cylindrical matrix pores with a diameter of 1–100 nm account for more than 97% of coal pore space, meaning that coal-bed methane (CBM) is primarily adsorbed in the matrix pores. , The slit-shaped cleat pores, however, are 0.1–10 μm in width and 1–3 cm in length. The cleats are well connected to one another and thus offer the major contribution to fluid mobility. , While the matrix pore contribution to fluid mobility is small, the desorption of methane (CH 4 ) therein results in significant matrix shrinkage and cleat permeability increase. , …”

Investigation on the pore characteristics of coal specimens with bursting proneness

“…27 and Zhao et al . 28 , the contact angle between mercury and pore surface was set to 130 degrees, and the surface tension of mercury was set to 0.485 J/m 2 .…”

Characteristics of Pore and Fracture of Coal with Bursting Proneness Based on DIC and Fractal Theory

“…Before MIP, the sample was dried at 373 k for 12 h, and then evacuated at 50 umHg for 8 min to discharge the residual gas and moisture. According to the suggestions of Gan et al [22] and Zhao et al [23], the contact angle between mercury and pore surface was set as 130 • and the mercury surface tension was set as 0.485 J/m 2 .…”