Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions
The permeability of the coal body is the key parameter restricting the efficient extraction of coalbed methane, and scholars have analysed it from two angles of the change of stress state and porosity of the coal body. However, there is still a lack of study on the mechanism of gas migration and mov...
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2019-10-01
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doaj-3d751b2dfbac4cd083fbd0c7b4d7263e2020-11-25T04:02:08ZengThe Royal SocietyRoyal Society Open Science2054-57032019-10-0161010.1098/rsos.190892190892Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditionsGang WangZhiyuan LiuYanwei HuCheng FanWenrui WangJinzhou LiThe permeability of the coal body is the key parameter restricting the efficient extraction of coalbed methane, and scholars have analysed it from two angles of the change of stress state and porosity of the coal body. However, there is still a lack of study on the mechanism of gas migration and movement in soft coalbed methane reservoir under the coupling between the true triaxial stress field (maximum principal stress σ1 > intermediate principal stress σ2 > minimum principal stress σ3) and the gas pressure field. In this paper, the coal gas adsorption and seepage experiments are conducted through the self-developed true triaxial ‘gas–solid’ coupled coal mass seepage system with gas as the adsorption and seepage medium and coal briquette taking the place of soft coalbed methane reservoirs. Furthermore, the coal gas adsorption deformation model and the permeability evolution model taking gas adsorption into account are developed. Through analysis of both experimental and theoretic results, the main conclusions are drawn as follows: (i) With the increase in gas pressure, the adsorption deformation variation of coal mass is divided into a slow growth zone, a stable growth zone and a rapid growth zone. (ii) The gas adsorption deformation model developed can predict the variation trend of coal mass adsorption volumetric strains for different types of soft coalbeds, and the fitting variance of experimental and theoretical volumetric strains is above 98%. (iii) With the increase in maximum principal stress difference, the coal permeability variation curve shows two obvious turning points, which can be divided into a slow reduction zone, a rapid reduction zone and a steady reduction zone. (iv) The permeability model of coal mass considering the gas adsorption effect can reflect the variation characteristics of permeability in the rapid reduction zone, and the overall fitting variance of experimental and theoretical permeabilities is above 91%. The above results could provide a reliable experimental and theoretical basis for improving coalbed methane extraction rates.https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.190892true triaxial stresssoft coalbedgas migrationpermeability model |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Gang Wang Zhiyuan Liu Yanwei Hu Cheng Fan Wenrui Wang Jinzhou Li |
spellingShingle |
Gang Wang Zhiyuan Liu Yanwei Hu Cheng Fan Wenrui Wang Jinzhou Li Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions Royal Society Open Science true triaxial stress soft coalbed gas migration permeability model |
author_facet |
Gang Wang Zhiyuan Liu Yanwei Hu Cheng Fan Wenrui Wang Jinzhou Li |
author_sort |
Gang Wang |
title |
Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions |
title_short |
Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions |
title_full |
Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions |
title_fullStr |
Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions |
title_full_unstemmed |
Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions |
title_sort |
influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions |
publisher |
The Royal Society |
series |
Royal Society Open Science |
issn |
2054-5703 |
publishDate |
2019-10-01 |
description |
The permeability of the coal body is the key parameter restricting the efficient extraction of coalbed methane, and scholars have analysed it from two angles of the change of stress state and porosity of the coal body. However, there is still a lack of study on the mechanism of gas migration and movement in soft coalbed methane reservoir under the coupling between the true triaxial stress field (maximum principal stress σ1 > intermediate principal stress σ2 > minimum principal stress σ3) and the gas pressure field. In this paper, the coal gas adsorption and seepage experiments are conducted through the self-developed true triaxial ‘gas–solid’ coupled coal mass seepage system with gas as the adsorption and seepage medium and coal briquette taking the place of soft coalbed methane reservoirs. Furthermore, the coal gas adsorption deformation model and the permeability evolution model taking gas adsorption into account are developed. Through analysis of both experimental and theoretic results, the main conclusions are drawn as follows: (i) With the increase in gas pressure, the adsorption deformation variation of coal mass is divided into a slow growth zone, a stable growth zone and a rapid growth zone. (ii) The gas adsorption deformation model developed can predict the variation trend of coal mass adsorption volumetric strains for different types of soft coalbeds, and the fitting variance of experimental and theoretical volumetric strains is above 98%. (iii) With the increase in maximum principal stress difference, the coal permeability variation curve shows two obvious turning points, which can be divided into a slow reduction zone, a rapid reduction zone and a steady reduction zone. (iv) The permeability model of coal mass considering the gas adsorption effect can reflect the variation characteristics of permeability in the rapid reduction zone, and the overall fitting variance of experimental and theoretical permeabilities is above 91%. The above results could provide a reliable experimental and theoretical basis for improving coalbed methane extraction rates. |
topic |
true triaxial stress soft coalbed gas migration permeability model |
url |
https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.190892 |
work_keys_str_mv |
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