Modeling Gas Adsorption–Desorption Hysteresis in Energetically Heterogeneous Coal and Shale

Abstract

Adsorption of gases in porous adsorbents such as coal and shale generally exhibits the phenomenon of hysteresis. Most of the previous studies on desorption hysteresis were conducted via experimental tests. However, few theoretical models that represent adsorption−desorption hysteresis of gases in porous sorbents are available. To address this issue, this work develops a new adsorption−desorption model for describing adsorption and desorption isotherms of gases with hysteresis. Particularly, the energetically heterogeneous surfaces of an adsorbent are considered via the patchwise model. Based on the change in site energy distribution, a logarithmically pressure-dependent hysteresis index, which is used to measure the degree of hysteresis, is derived for quantitative assessment of the degree of hysteresis. Besides, the correlation between the desorption isotherm and initialized pressure for desorption is established. The accuracy of the proposed model to adequately describe the adsorption−desorption hysteresis of gas in coal and shale is demonstrated by validating the model against laboratory experiments obtained from the literature. The results indicate that the adsorption isotherm depends significantly on site energy distribution. By comparing the site energy distributions for adsorption and desorption isotherms, it is found that the desorption hysteresis can be attributed to the change in pore size distribution caused by adsorption-induced deformation. The analyses support that the proposed model can be used as an effective tool to quantitatively predict the amount of released gas during desorption, which is significant for designing coalbed methane or shale gas production and assessing long-term CO 2 storage behavior.

CO2 Injection via a Horizontal Well into the Coal Seam at the Experimental Mine Barbara in Poland

“…The results of the laboratory tests and numerical modeling activities [45][46][47][48][49][50][51][52][53] provided useful insights into potential scenarios of the in situ CO 2 injection operation. These helped to determine the final location and position of the wells, and the results suggested that the maximum migration of the injected CO 2 during the experiment was approximately a dozen meters.…”

Quantitative Evaluation of the Influence of Injected Water on Methane Desorption Behaviors of Coal in the Ordos Basin

“…As mentioned above, most of the existing literature provides qualitative analysis of the effect of water on gas desorption, but the microscopic influencing mechanism of water injection on gas desorption in coal seams is less studied. − This paper presents a study of the influence of water injection on gas desorption behavior in coal seams and reveals its influencing mechanism. The research results can provide theoretical support for gas control in underground coal mines.…”

Low Subcritical CO2 Adsorption–Desorption Behavior of Intact Bituminous Coal Cores Extracted from a Shallow Coal Seam

“…Adsorption in mesopores contributes significantly to the total adsorption in well-developed mesopore surfaces. − Recent molecular simulation studies on pore network models reveal that the intricate mechanisms of fluid–wall and fluid–fluid interactions, which have an effect on the gas transport mechanism in porous media, have an influence on the mechanism . The network models also account for the pore-blocking effects during desorption, which are manifested as hysteresis . Surface chemistry of carbonaceous materials can play an important role in gas adsorption.…”

“… 34 The network models also account for the pore-blocking effects during desorption, which are manifested as hysteresis. 35 Surface chemistry of carbonaceous materials can play an important role in gas adsorption. For example, functional groups, such as carboxyl and hydroxyl groups, accommodate CO 2 molecules at the sorption sites via surface polarity or molecular bonds.…”