Study on microstructural changes of coal after methane adsorption

This study analyzes the microstructure and deformation rule after methane adsorption on coal by scanning electron microscopy (SEM) and computed tomography (CT) scanning of microscopic coal samples. Studies have shown that coal is a natural rock composed of vitrinite coal matrix and clay mineral. After methane adsorption, coal undergoes non-uniform expansion deformation. This occurrence prompts coal density to decrease and then increase, causing the density distribution of coal to become highly concentrated. During swelling after adsorption, the effects of deformation and expansion on coal structures become stronger than that of mutual squeezing. Under low adsorption pressure, coal expansion deformation is more likely to crack the pore structure of the original coal to acquire space for expansion. When the adsorption pressure increases, compression becomes mainly concentrated in the low-density region; as adsorption pressure continues to increase, expansion deformation occurs from high-density to low-density regions. The methane adsorption properties of coal are related to its pore structure. Adsorption and swelling mainly occur in the region where the pore structure is unfilled or filled with clay minerals. Expansion deformation conforms to the Langmuir equation; the region without pore structure development exhibits no swelling; the deformation degree and range of the pore structure and clay mineral mixing zone exhibit increase volatility. Overall, results reveal a microstructural change after methane adsorption. (C) 2016 Elsevier B.V. All rights reserved.