Influences of controlled microwave field irradiation on physicochemical property and methane adsorption and desorption capability of coals: Implications for coalbed methane (CBM) production

Role of H2O of Gas-Bearing Shale in Its Physicochemical Properties and CH4 Adsorption Performance Alteration Due to Microwave Irradiation

“…As illustrated in Figure a, the pores in the shale matrix mainly include organic matter pores, interparticle pores in quartz and clay minerals, dissolution pores in carbonate minerals, and intraparticle pores in clay aggregates . Therefore, the possible factors accounting for the pore structural parameter of the shale matrix change due to microwave irradiation typically comprise mineral decomposition, clay shrinkage, organic matter decomposition and conversion, small organic matter release, and asphaltene and kerogen conversion (Figure b). , Particularly, the temperature of the shale matrix increases under the microwave field, therefore causing decomposition of organic matter and carbonate minerals and releasing small-molecule hydrocarbons and CO 2 , respectively, thus producing some new nanopores. , Additionally, clay minerals lose their interlayer H 2 O due to microwave irradiation, causing clay shrinkage and leading to widened layer spacing . Moreover, asphaltene and kerogen could convert to metaplast with rising temperature of the shale matrix under microwave irradiation, blocking the pore throat and leading to decrease of the pore surface area and pore volume of the shale matrix. , Therefore, given the aforementioned decreasing S meso and V meso of the shale sample, the negative effect of conversion of asphaltene and kerogen on the pore structure of the shale matrix is dominant among all the factors.…”

“…30 Therefore, the possible factors accounting for the pore structural parameter of the shale matrix change due to microwave irradiation typically comprise mineral decomposition, clay shrinkage, organic matter decomposition and conversion, small organic matter release, and asphaltene and kerogen conversion (Figure 6b). 25,29 Particularly, the temperature of the shale matrix increases under the microwave field, therefore causing decomposition of organic matter and carbonate minerals and releasing small-molecule hydrocarbons and CO 2 , respectively, thus producing some new nanopores. 20,25 Additionally, clay minerals lose their interlayer H 2 O due to microwave irradiation, causing clay shrinkage and leading to widened layer spacing.…”

“…Given the difference in the dielectric constant and loss factor among various kinds of inorganic minerals, thermal stress is likely to occur in the interface between different inorganic minerals or inside the same inorganic mineral. Provided that the generated thermal stress exceeds mechanical strength of inorganic minerals, fracture will appear within the shale matrix and further increase shale reservoir permeability (Figure c), − thereby making CH 4 flow within the reservoir more easily . Overall, microwave irradiation has capability of enhancing desorption, diffusion, and flow performance of CH 4 within the shale reservoir.…”

Evaluation and analysis of methane adsorption capacity in deep‐buried coal seams

“…Coal contains constricted micropores with narrow pore throats which are smaller than the kinetic diameters of methane, and the gas molecules would further block the pore throats as the pressure rises. The change of pore throats results in the difference of energy required for gas molecules to enter and escape from the constricted pores 43–45 . Practically, this is important for field application since both CBM and coalmine gas drainage operations under deep burial conditions.…”

“…The change of pore throats results in the difference of energy required for gas molecules to enter and escape from the constricted pores. [43][44][45] Practically, this is important for field application since both CBM and coalmine gas drainage operations under deep burial conditions. The increase in coal seam depth leads to temperature rise, which weakens the phenomenon of desorption hysteresis in the process of gas desorption.…”