Analysis of Logging Identification and Methane Diffusion Properties of Coals with Various Deformation Structures

Abstract

Methane diffusion in coals with different deformations is important for gas resource evaluation. In this study, the adsorption/ desorption and diffusion behavior in different coal structures were investigated, and the multi-logging parameter model of backpropagation (BP) neural network was employed to identify coal structures, as well as the effects of diffusion changes on gas contents in the study area, were revealed. The results indicate that with the increase of coal deformation intensity, the Langmuir V L increases, and both specific surface area and pore volume increase as well. Diffusion coefficients in coals decrease gradually with the decrease of pressures, and the development of meso/macropores and micropores in tectonic coals promotes gas migration, which increase the diffusion efficiency, especially the fast and reduction diffusion stages (S1 and S2).Comparisons between intact and tectonically deformed coals in terms of gas diffusion behaviors modeled by the unipore and bidisperse numerical methods show that the analytical solution of the bidisperse model is more appropriate to describe diffusion behaviors in tectonic coals due to the enhanced complexity of mesopores and micropores in coals. Different coal structures exhibiting similar values in well logs lead to multiple interpretations of coal structures. The proposed BP model is an effective way to identify the nonlinear relationships between well logs and coal structures by extracting key information from logging datasets. The modeled results show that the degree of heterogeneity of the gas content in different coal structures is high and the higher diffusion rate in granulated coal zone somewhat reduced the measured gas content.

Evaluation of coalbed methane resources in Xinjing Baoan block based on PCA, TOPSIS, & MLFM

“…According to the degree of damage, the coal structure can be divided into four types: primary structure coal, fragmentary coal, fragmentary coal and mylonite coal. Fragmentary and mylonite coal are also known as tectonic coal, which is not conducive to CBM development owing to its structure, disordered fracture direction, poor connectivity, and relatively low permeability (Wu et al, 2021;Zhang et al, 2021aZhang et al, , 2021b. Based on the analysis of well drilling results and logging data, we can see that both primary and structural coal developed in the Baoan blocks.…”

“…15 coal seam mainly developed along the NNE direction of fault DF 4 , which is subjected to weak tectonic stress. Most faults only developed in the coal seam, and the coal structure did not suffer severe damage (Cao et al, 2021;Zhang et al, 2021bZhang et al, , 2021c) (Figure 8).…”

“…However, there exists limited research on CBM selection using TOPSIS. In addition, factors of CBM development potential evaluation not only restrict and influence each other, but also possess repeated information among a large number of indicators, resulting in the complexity and uncertainty of CBM selection evaluation and decision-making system (Hower et al, 2021; Ye et al, 2022; Zhang et al, 2021a). Principal component analysis is a type of evaluation method that can deal with information jumbled in decision systems and evaluation systems.…”