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The permeability of coal is an indispensable parameter for predicting the coalbed methane (CBM) and enhanced CBM (ECBM) production. Considering the low permeability characteristics of coal, the permeability is usually measured by the transient technique in the laboratory. Normally, it is assumed that the calculated permeability will not greatly vary if the pulse pressure applied in the experiment is small (less than 10% of pore pressure) and previous studies have not focused on the effect of the pulse pressure on the measurement permeability. However, for sorptive rock, such as coals and shales, the sorption effect may cause different measurement results under different pulse pressures. In this study, both nonadsorbing gas (helium) and adsorbing gas (carbon dioxide) were used to investigate the adsorption effect on the gas permeability of coal measurement with the pulse-decay technique. A series of experiments under different pore pressures and pulse pressures was performed, and the carbon dioxide permeability was calculated by both Cui et al.'s and Jones' methods. The results show that the carbon dioxide permeability calculated by Jones' method was underestimated because the adsorption effect was not considered. In addition, by comparing the helium and carbon dioxide permeabilities under different pulse pressures, we found that the carbon dioxide permeability of coal was more sensitive to the pulse pressure due to the adsorption effect. Thus, to obtain the accurate permeability of coal, the effect of adsorption should be considered when measuring the permeability of adsorptive media with adsorbing gas by the transient technique, and more effort is required to eliminate the effect of the pulse pressure on the measured permeability. [ABSTRACT FROM AUTHOR]

Injecting CO2 into a reservoir disturbs the geostress field, which leads to variations in the permeability of caprock and affects its sealing performance. In this paper, the evolution characteristics of the permeability of Yingcheng mudstone were experimentally studied during deviatoric compression under different confining pressures. As the confining pressure increased, the strength of the mudstone increased bilinearly, the angle between the fault and the maximum principle stress increased, and the fault became flatter. During compression, the permeability of mudstone first decreased and then increased and the turning point of the permeability was between the onset of dilatancy and the turning point of volumetric strain; when the fault formed, the permeability increased sharply and the fault-induced increment was reduced exponentially with increasing confining pressure. In addition, the mudstone transformed to the ductile failure mode when the effective confining pressure was greater than 35 MPa, which means that the permeability did not jump within a small strain. Finally, a practical strain-based model of permeability evolution that separately considers compaction and dilatancy was proposed, and the predicted permeability values were in good agreement with the experimental results. This study revealed the effect of confining pressure on permeability evolution during compression and can help evaluate the sealing ability of mudstone caprock. [ABSTRACT FROM AUTHOR]

CO 2 geological utilization (CGU) technologies have a great potential to enable large-scale CO 2 storage at reasonable cost and is widely considered to be a strategic technology option to help reduce CO 2 emissions. CGU technology can be applied to enhance the recovery of oil (CO 2 -EOR), natural gas (CO 2 -EGR), underground water (CO 2 -EWR), coal-bed methane (CO 2 -ECBM), shale gas (CO 2 -ESGR), geothermal energy (CO 2 -EGS), in situ uranium leaching (CO 2 -IUL), and others. The first step in evaluating of CGU technologies is to determine the storage resource, technical readiness, and geographical distribution of CO 2 storage resources. This paper presents preliminary evaluation results on storage resource, technology readiness level and geographic distribution of onshore CGU in China; the results were obtained by performing a resource evaluation methodology, technology readiness level (TRL) method, and geographic information system tool. Results indicate a significant resource for onshore CGU technologies and good proximity in some parts of China. However, CO 2 storage resources with high TRLs and low cost are located in the northeast, northwest, and southeast regions and not in the south and coastal areas of China, where most CO 2 emission sources locate. Therefore, the timeframes and options for CGU deployment in different regions vary. This situation indicates that different regions have to perform CO 2 mitigation by employing different CGU technologies at different timeframes. [ABSTRACT FROM AUTHOR]

Abstract: Gas mixture, consisting mainly of N2 and a small amount of CO2, enhanced coalbed methane recovery (G-ECBM) technology is a way to enhance low permeability coals’ methane recovery, by taking advantage of the permeability-enhancing role of N2. Two different scale pilot filed tests of G-ECBM have been carried out in Pingdingshan Coal Mine and in Lu’an Coal Mine. The two pilot tests were all conducted in underground tunnel. Tests results showed that, compared with existing conventional extraction method, G-ECBM technology had great breakthrough in principle and effect, and was technically feasible; gas injection had effects on not only the neighbouring production wells but also the a-little-far production wells; gas injection enhanced the concentration and flow rate of coalbed methane. [Copyright &y& Elsevier]

Abstract: Injections of carbon dioxide (CO2) into unmineable coalbeds can both enhance coalbed methane recovery (ECBM), a high-efficiency energy, and realize underground storage of CO2. In these processes, the diffusion and sorption of methane (CH4) and carbon dioxide are key dominant processes. In this study, the diffusion and sorption behavior of CH4 and CO2 in coal are investigated and compared based on molecular simulation. The calculated diffusion coefficient of CO2 was in the order of 10−9 m2/s, which is reasonably close to the experimental result. The sorption isotherms were obtained using the grand canonical Monte Carlo method. Coal tended to adsorb more CO2 than CH4 at a given temperature and pressure. The sorption heat of CO2 was larger than that of CH4 (7.9 and 5.8 kcal/mol respectively), accounting for the fact that the CH4 adsorbed in the coal seam could be replaced by CO2. This presents an alternative method for directly studying the interactions between coal macromolecule and small-molecule gases under various external environments. [Copyright &y& Elsevier]