TY - JOUR
T1 - Brittleness evolution of different rank coals under the effects of cyclic liquid CO2 during the coalbed methane recovery process
AU - Zhai, Cheng
AU - Xu, Jizhao
AU - Sang, Shuxun
AU - Ranjith, P. G.
AU - Yu, Xu
AU - Sun, Yong
AU - Cong, Yuzhou
AU - Tang, Wei
AU - Zheng, Yangfeng
N1 - Funding Information:
The authors gratefully acknowledge the financial support from the Open Fund of Jiangsu Key Laboratory of Coal-Based Greenhouse Gas Control and Utilization (2020ZDZZ02A, 2020ZDZZ01D), the National Natural Science Foundation of China (52104228, 51774278), China Postdoctoral Science Foundation (2021M693409), and the National Science Fund for Distinguished Young Scholars (51925404).
Publisher Copyright:
© 2021 American Chemical Society
PY - 2021/11/4
Y1 - 2021/11/4
N2 - The understanding of brittleness evolution for coals influenced by cyclic liquid CO2 effects has great significance to evaluate the crack capacity of the matrix. A brittleness index (B) calculation model was established on the basis of the statistical damage constitutive equation and the stress−strain curves, without considering their primary curve patterns, that was mainly controlled by elastic modulus (E), compressive strength (σc), and the corresponding strain (εc). Three different rank coals were processed under the temperature effect and the temperature and adsorption coupling effect that originated from cyclic liquid CO2 and then were destroyed by the uniaxial compression test. With the increasing liquid CO2 parameters [cyclic number (CN) and total cyclic time (TCT)], the σc of the different rank coals decreased gradually, while the εc did not have an apparent change tendency that was greatly influenced by the coal anisotropy (the nonuniform deformation responses to the temperature effect and the primary crack complexity) and the capacity of CO2 adsorption decreasing the free surface energy. The B values of lignite and bitumite showed a declining trend, while those of anthracite did not have obvious laws, because of the lack of laws for εc. The relationships between B and CN/TCT indicated that the larger the cyclic parameters, the smaller the B values and the greater the coal destruction degree. The E and σc had positive relationships with the B calculations, while the Poisson's ratio (μ), damage variable (Dv), and accumulated energy (J) did not have obvious correlations with the B values. The introduction of liquid CO2 induced a huge number of unrecoverable deformations and fatigue damages to be generated, leading to a large plastic region and decreasing the coal brittleness. The results might be helpful to evaluate the capacity of liquid CO2 fracturing and to estimate the efficiency of coalbed methane recovery.
AB - The understanding of brittleness evolution for coals influenced by cyclic liquid CO2 effects has great significance to evaluate the crack capacity of the matrix. A brittleness index (B) calculation model was established on the basis of the statistical damage constitutive equation and the stress−strain curves, without considering their primary curve patterns, that was mainly controlled by elastic modulus (E), compressive strength (σc), and the corresponding strain (εc). Three different rank coals were processed under the temperature effect and the temperature and adsorption coupling effect that originated from cyclic liquid CO2 and then were destroyed by the uniaxial compression test. With the increasing liquid CO2 parameters [cyclic number (CN) and total cyclic time (TCT)], the σc of the different rank coals decreased gradually, while the εc did not have an apparent change tendency that was greatly influenced by the coal anisotropy (the nonuniform deformation responses to the temperature effect and the primary crack complexity) and the capacity of CO2 adsorption decreasing the free surface energy. The B values of lignite and bitumite showed a declining trend, while those of anthracite did not have obvious laws, because of the lack of laws for εc. The relationships between B and CN/TCT indicated that the larger the cyclic parameters, the smaller the B values and the greater the coal destruction degree. The E and σc had positive relationships with the B calculations, while the Poisson's ratio (μ), damage variable (Dv), and accumulated energy (J) did not have obvious correlations with the B values. The introduction of liquid CO2 induced a huge number of unrecoverable deformations and fatigue damages to be generated, leading to a large plastic region and decreasing the coal brittleness. The results might be helpful to evaluate the capacity of liquid CO2 fracturing and to estimate the efficiency of coalbed methane recovery.
UR - https://www.scopus.com/pages/publications/85118759825
U2 - 10.1021/acs.energyfuels.1c02887
DO - 10.1021/acs.energyfuels.1c02887
M3 - Article
AN - SCOPUS:85118759825
SN - 0887-0624
VL - 35
SP - 17651
EP - 17662
JO - Energy & Fuels
JF - Energy & Fuels
IS - 21
ER -