Effect of Cyclical Microwave Modification on the Apparent Permeability of Anthracite: A Case Study of Methane Extraction in Sihe Mine, China

Self Cite

Ultrasonic is a new method to enhance coalbed methane recovery. A deeper comprehension of the synergistic mechanisms of combined ultrasonicchemical modification on the CH 4 adsorption−desorption capability and physicochemical properties of coal is necessary for potential field implementation, as the modification of coal reservoirs frequently necessitates the addition of chemical reagents. This paper evaluated the CH 4 adsorption−desorption properties of anthracite modified by sodium dodecyl sulfate (SDS) solution, ultrasonic modification, and combined ultrasonic-SDS modification. Fourier transform infrared spectroscopy, low-temperature nitrogen adsorption, and micro-CT were applied to elucidate the synergistic mechanism of the combined modification. The research results show that the SDS solution reduces the saturated adsorption capacity of anthracite and increases its final desorption rate by dissolving clay minerals and the physical adsorption masking effect of SDS micelles on the coal surface. Some surface groups with low bond energy are broken or evaporated under mechanical vibration and thermal effects generated by ultrasonic. The original fractures are expanded and connected, which changes the adsorption−desorption properties of anthracite. The synergistic effect of the combined modification of ultrasonic-SDS can promote the penetration range and chemical reaction efficiency of the SDS solution, which expands the effective range of ultrasonic. After combined modification, the amount of aromatics, oxygencontaining functional groups, and aliphatic hydrocarbons on the surface of coal is reduced. The connected porosity of coal samples accounts for 91.5% of the total porosity. As a result, the saturated adsorption capacity of anthracite reduces by 26.7%, and the final desorption rate increases by 28.0%. The effect of the combined ultrasonic-chemical modification is better than that of a single modification.

Section: Resultsmentioning

confidence: 99%

Synergistic Mechanism of Ultrasonic-Chemical Effects on the CH₄ Adsorption–Desorption and Physicochemical Properties of Jincheng Anthracite

Liang

Kang

et al. 2022

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“…Zhang et al found that a decrease in alkane side chain abundance reduced the methane adsorption capacity. 59 Meng et al 60 and Hao et al 61 found that pore entrances may be blocked and that the dispersed interactions of methane with small pore walls may be reduced by oxygen-containing functional groups; that is, a higher oxygen content would weaken the methane adsorption performance in coals. In addition, the decomposition of some sulfur-containing minerals such as pyrite weakens the methane adsorption capacity in coal.…”

Section: Resultsmentioning

confidence: 99%

“…In particular, the decrease in the number of alkane side chains (Figure f) and the oxidation of carboxyl groups (Figure h) made the largest contributions to the reduced methane adsorption performance in coal. Zhang et al found that a decrease in alkane side chain abundance reduced the methane adsorption capacity . Meng et al and Hao et al found that pore entrances may be blocked and that the dispersed interactions of methane with small pore walls may be reduced by oxygen-containing functional groups; that is, a higher oxygen content would weaken the methane adsorption performance in coals.…”

Section: Results and Discussionmentioning

confidence: 99%

Response of Molecular Structures and Methane Adsorption Behaviors in Coals Subjected to Cyclical Microwave Exposure

Zhang

Kang

et al. 2021

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To better understand the methane adsorption behavior after microwave exposure, the importance of quantitatively characterizing the effect of cyclical microwave exposure on the molecular structures of coals cannot be overemphasized, with implications for enhancing coalbed methane (CBM) extraction. Thus, cyclical microwave exposure experiments of three different metamorphic coals were conducted, and the methane adsorption capacity before and after each microwave exposure (10 in total) for 120 s was evaluated. Fourier transform infrared spectroscopy analysis and peak fitting technology were applied to quantitatively characterize the changes in the structural parameters of coal molecules. The results showed that after modification, the structural parameters like aromatic carbon fraction (f a–F), aromaticity (I 1 and I 2), degree of condensation (DOC 1 and DOC 2), and the maturity of organic matter (“C”) gradually increased with increasing exposure times, while the length of the aliphatic chain or its branching degree (CH 2/CH 3) and the hydrocarbon generating capacity (“A”) showed a decreasing trend. The Langmuir volume (V L) of three different rank coal samples decreased from 29.2, 32.8, and 40.4 mL/g to 25.7, 29.3, and 35.7 mL/g, respectively; the Langmuir pressure (P L) increased from 0.588, 0.844, and 0.942 MPa to 0.626, 1.007, and 1.139 MPa, respectively. The modification mechanism was investigated by analyzing the relationship between the methane adsorption behaviors and molecular structures in coals. The release of alkane side chains and the oxidation of oxygen-containing functional groups caused by microwave exposure decreased the number of methane adsorption sites. As a result, the methane adsorption capability decreased. In addition, the decomposition of minerals affects methane adsorption behaviors in coals. This work provides a basis for microwave modification of coal as well as in situ enhancement of CBM extraction using microwave exposure.

“…In recent years, unconventional resources such as coalbed methane (CBM), shale gas, and tight sandstone gas have attracted widespread attention, and the exploitation theory and technology are developing rapidly . However, commercial gas production has been hampered by the low permeability of coal seams in China. , Thus, permeability-improving methods, including protective seam mining, hydraulic fracturing, , hydraulic cutting, , microwave modification, and blasting-induced fracturing, , increase massive fractures in coal seams, which greatly reduce gas pressure in the early stage of extraction and improve the gas extraction rate. However, extraction is difficult in the later stage because of little variation in gas pressure and a lack of driving force, and the generated coal fines block fractures and boreholes and further cause permanent damage to permeability .…”

Section: Introductionmentioning

confidence: 99%

Characterization of Pore Structures with Mercury Intrusion Porosimetry after Electrochemical Modification: A Case Study of Jincheng Anthracite

Guo

Zhang

et al. 2022

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Quantitative characterization of the change in the cleat and pore structures and fractal dimensions in anthracite after electrochemical modification is crucial for better understanding of the modification effect. Thus, lump anthracite samples were electrochemically modified in our manufactured device with 0, 0.5, 1, and 2 V/cm potential gradients. The changes in heterogeneity and porosity after modification were tested and analyzed by mercury intrusion porosimetry (MIP) and fractal theory. The results indicated that the total volume of the pores increased after electrochemical treatment and continuously increased with increasing potential gradient during the treatment process. After modification, the number of pores or fractures with a pore size between 6 and 20 μm in coal after modification increases significantly. According to the intrusion pressure, three stages were defined as lower ( P M < 0.1 MPa), intermediate (0.1 ≤ P M < 10 MPa), and higher regions ( P M ≥ 10 MPa), which are characterized by fractal dimensions D 1 , D 2 , and compression stages, respectively. After modification, the fractal dimension D 1 showed an increasing trend, while the fractal dimension D 2 showed a decreasing trend, indicating that the fracture system became more complicated and that the pore system became more regular after electrochemical treatment. The evolution mechanism of heterogeneity and porosity and their fractal dimensions were explained by the dissolution of minerals, change in pH values, and dynamics of temperatures during the process of modification. The results obtained in this work are of important guiding significance for coalbed methane (CBM) extraction via in situ modification by electrochemical treatment.