Fracturing evolution mechanisms of eroded coals under the temperature effect of the CO₂-H₂O system

Authors

LIN Baiquan, School of Safety Engineering, China University of Mining & Technology, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, ChinaFollow
SHI Yu, School of Safety Engineering, China University of Mining & Technology, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, ChinaFollow
LIU Ting, School of Safety Engineering, China University of Mining & Technology, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China
SHEN Yang, School of Safety Engineering, China University of Mining & Technology, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China
HUANG Tao, School of Safety Engineering, China University of Mining & Technology, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China

Abstract

Background Injecting hot flue gas produced and discharged by gas-fired power plants into deep coal seams where gas is difficult to extract enjoys dual benefits: gas production growth and geologic CO₂ sequestration. However, there is an urgent need to determine the impact of the heat-carrying property of hot flue gas on the stability of coal reservoirs. To address this issue, the key is to clarify the fracturing evolution mechanisms of eroded coals under the temperature effect of the CO₂-H₂O system.Methods Using the independently built platform of CO₂-H₂O-coal interactions that consider the temperature-pressure coupling effect, this study preprocessed coal specimens through uniaxial loading, triaxial loading, and Brazilian splitting under different temperatures. Based on the results of mechanical strength tests of the coal specimens, this study investigated the nonlinear deterioration pattern of coal strength under different temperatures of the CO₂-H₂O system. By comparing the acoustic emission (AE) and non-contact, full-field strain digital image correlation (DIC) monitoring results during the loading processes, this study analyzed the impacts of the temperature of the CO₂-H₂O system on the fracturing evolution of eroded coals. In combination with scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM-EDS), this study explored the competitive degradation effect arising from thermal fracturing and mineral dissolution under different erosion temperatures. Results and Conclusions The results indicate that with an increase in the erosion temperature, the progressive fracturing stage of coal specimens subjected to uniaxial loading shifted from pre-peak stress to post-peak stress. Meanwhile, the competitive degradation effect induced by thermal fracturing and mineral dissolution led to a nonlinear decrease in the peak strength of the coal specimen. For the coal specimens subjected to splitting, mineral dissolution led to significantly decreased tensile strength as the erosion temperature increased, while thermal fracturing did not significantly aggravate their tensile strength degradation. In the case of low-temperature erosion of the coal specimens, mineral dissolution resulted in microscopic defects, which were interconnected to form numerous new fractures during specimen loading. As a result, both the frequency of abrupt changes in the AE ringing count and cumulative AE ringing counts increased. In the case of high-temperature erosion, thermal fracturing resulted in numerous connected fractures in the coal specimens, leading to a significant decrease in both the frequency of abrupt changes in AE ringing counts and the cumulative AE ringing counts. Accordingly, the specimen fracturing gradually shifted from rapid and sudden tensile fracturing to progressive and slow shear fracturing. As the erosion temperature rose, the macroscopic fracturing morphology of the coal specimens subjected to uniaxial loading underwent flaky separation, the separation of shear blocks, and mixed fracturing, sequentially. This led to a more complex distribution of macroscopic fractures and more complete fracturing. Meanwhile, numerous microscopic defects were formed within the eroded specimen, promoting shear fracturing. However, tensile fracturing remained predominant in the case of peak stress. Concurrently, the zones lagging behind featured strain concentration and complex strain fields. For the coal specimens subjected to splitting, the macroscopic fracturing morphology gradually evolved from central fracturing to more tortuous non-central rupture. Furthermore, the coal specimens showed complex tensile strain distributions, and the tensile strain concentration areas enlarged and deflected toward one side of the specimens. The mineral dissolution effect can produce only dissolution pits and holes inside the coal specimens, while large-scale fractures can be formed in a relatively long erosion time. Under high-temperature erosion, the mineral dissolution effect greatly decreased. In contrast, the thermal fracturing effect resulted in numerous new fractures on a larger scale, leading to significantly decreased mechanical strength of coals. The results of this study can provide a theoretical reference for the hot flue gas-enhanced gas production growth and the stability evaluation of reservoirs during geologic CO₂ sequestration.

Keywords

hot flue gas, temperature effect, eroded coal, fracturing evolution, competitive degradation

DOI

10.12363/issn.1001-1986.25.04.0245

Recommended Citation

LIN Baiquan, SHI Yu, LIU Ting, et al. (2025) "Fracturing evolution mechanisms of eroded coals under the temperature effect of the CO₂-H₂O system," Coal Geology & Exploration: Vol. 53: Iss. 8, Article 3.
DOI: 10.12363/issn.1001-1986.25.04.0245
Available at: https://cge.researchcommons.org/journal/vol53/iss8/3

Reference

[1] 闫霞，徐凤银，熊先钺，等. 深部煤层气勘探开发关键实验技术及发展方向[J]. 煤田地质与勘探，2025，53(1)：128−141.

YAN Xia，XU Fengyin，XIONG Xianyue，et al. Key experimental technologies and their development directions for the exploration and production of deep coalbed methane[J]. Coal Geology & Exploration，2025，53(1)：128−141.

[2] 李国富，李超，张碧川，等. 我国煤矿瓦斯抽采与利用发展历程、技术进展及展望[J]. 煤田地质与勘探，2025，53(1)：77−91.

LI Guofu，LI Chao，ZHANG Bichuan，et al. Gas drainage and utilization in coal mines in China：History，technological advances，and prospects[J]. Coal Geology & Exploration，2025，53(1)：77−91.

[3] WANG Liang，SUN Yiwei，ZHENG Siwen，et al. How efficient coal mine methane control can benefit carbon–neutral target：Evidence from China[J]. Journal of Cleaner Production，2023，424：138895.

[4] 桑树勋，刘世奇，韩思杰，等. 中国煤炭甲烷管控与减排潜力[J]. 煤田地质与勘探，2023，51(1)：159−175.

SANG Shuxun，LIU Shiqi，HAN Sijie，et al. Coal methane control and its emission reduction potential in China[J]. Coal Geology & Exploration，2023，51(1)：159−175.

[5] 张金超，桑树勋，韩思杰，等. 不同含水性无烟煤CO₂吸附行为及其对地质封存的启示[J]. 煤田地质与勘探，2022，50(9)：96−103.

ZHANG Jinchao，SANG Shuxun，HAN Sijie，et al. CO₂ adsorption of anthracite with different moisture contents and its implications for geological storage[J]. Coal Geology & Exploration，2022，50(9)：96−103.

[6] 李四海，马新仿，张士诚，等. CO₂–水–岩作用对致密砂岩性质与裂缝扩展的影响[J]. 新疆石油地质，2019，40(3)：312−318.

LI Sihai，MA Xinfang，ZHANG Shicheng，et al. Experimental investigation on the influence of CO₂–brine–rock interaction on tight sandstone properties and fracture propagation[J]. Xinjiang Petroleum Geology，2019，40(3)：312−318.

[7] 桑树勋，牛庆合，曹丽文，等. 深部煤层CO₂注入煤岩力学响应特征及机理研究进展[J]. 地球科学，2022，47(5)：1849−1864.

SANG Shuxun，NIU Qinghe，CAO Liwen，et al. Mechanical response characteristics and mechanism of coal–rock with CO₂ injection in deep coal seam：A review[J]. Earth Science，2022，47(5)：1849−1864.

[8] 王志坚. CO₂相态变化致裂对煤层吸附性影响机理研究[J]. 油气藏评价与开发，2024，14(6)：967−974.

WANG Zhijian. Mechanism study on effect of CO₂ phase transition fracturing on methane adsorption in coal[J]. Petroleum Reservoir Evaluation and Development，2024，14(6)：967−974.

[9] 秦雷，王平，李树刚，等. 液态CO₂–水蒸气循环冲击煤体增透及瓦斯抽采效果模拟[J]. 煤田地质与勘探，2024，52(9)：67−79.

QIN Lei，WANG Ping，LI Shugang，et al. Coal permeability enhancement via cyclic percussion using low–temperature liquid CO₂ and high–temperature water vapor and simulations of resultant gas drainage performance[J]. Coal Geology & Exploration，2024，52(9)：67−79.

[10] PERERA M S A，RANJITH P G，PETER M. Effects of saturation medium and pressure on strength parameters of Latrobe Valley brown coal：Carbon dioxide，water and nitrogen saturations[J]. Energy，2011，36(12)：6941−6947.

[11] 刘佳佳，许艳之，聂子硕，等. 超临界CO₂作用下高阶煤微观结构及力学特性–声发射特征研究[J]. 煤炭科学技术，2024，52(10)：127−135.

LIU Jiajia，XU Yanzhi，NIE Zishuo，et al. Experimental study of microstructure and mechanical properties–acoustic emission characterization of high–rank coal under supercritical CO₂ action[J]. Coal Science and Technology，2024，52(10)：127−135.

[12] 贾毅超，杨栋，黄旭东，等. 超临界CO₂对无烟煤力学强度劣化机制及其微观结构演变特征[J]. 煤炭科学技术，2024，52(11)：323−336.

JIA Yichao，YANG Dong，HUANG Xudong，et al. Mechanism of mechanical strength degradation and microstructure evolution of anthracite induced by supercritical carbon dioxide[J]. Coal Science and Technology，2024，52(11)：323−336.

[13] 梁卫国，贺伟，阎纪伟. 超临界CO₂致煤岩力学特性弱化与破裂机理[J]. 煤炭学报，2022，47(7)：2557−2568.

LIANG Weiguo，HE Wei，YAN Jiwei. Weakening and fracturing mechanism of mechanical properties of coal and rock caused by supercritical CO₂[J]. Journal of China Coal Society，2022，47(7)：2557−2568.

[14] 肖畅，王开，张小强，等. 超临界CO₂作用后无烟煤力学损伤演化特性及机理[J]. 煤炭学报，2022，47(6)：2340−2351.

XIAO Chang，WANG Kai，ZHANG Xiaoqiang，et al. Mechanical damage evolution characteristics and mechanism of anthracite treated with supercritical CO₂[J]. Journal of China Coal Society，2022，47(6)：2340−2351.

[15] VISHAL V，RANJITH P G，SINGH T N. An experimental investigation on behaviour of coal under fluid saturation，using acoustic emission[J]. Journal of Natural Gas Science and Engineering，2015，22：428−436.

[16] ZHANG X G，RANJITH P G，RANATHUNGA A S，et al. Variation of mechanical properties of bituminous coal under CO₂ and H₂O saturation[J]. Journal of Natural Gas Science and Engineering，2019，61：158−168.

[17] ZHANG Guanglei，RANJITH P G，LI Zhongsheng，et al. Long–term effects of CO₂–water–coal interactions on structural and mechanical changes of bituminous coal[J]. Journal of Petroleum Science and Engineering，2021，207：109093.

[18] 薛熠，张家辉，刘嘉，等. 高温煤岩液氮冷却后巴西劈裂破坏及声发射演化特征[J]. 工程科学与技术，2025，57(1)：177−188.

XUE Yi，ZHANG Jiahui，LIU Jia，et al. Characteristics of Brazilian splitting failure and acoustic emission evolution of high–temperature coal after liquid nitrogen cooling treatment[J]. Advanced Engineering Sciences，2025，57(1)：177−188.

[19] 蔚立元，李光雷，苏海健，等. 高温后无烟煤静动态压缩力学特性研究[J]. 岩石力学与工程学报，2017，36(11)：2712−2719.

YU Liyuan，LI Guanglei，SU Haijian，et al. Experimental study on static and dynamic mechanical properties of anthracite after high temperature heating[J]. Chinese Journal of Rock Mechanics and Engineering，2017，36(11)：2712−2719.

[20] LIU Ting，LI Mingyang，LI Jianfeng，et al. Interactions of CO₂–H₂O–coal and its impact on micro mechanical strength of coal[J]. Geoenergy Science and Engineering，2023，227：211915.

[21] WANG Xiao，PAN Lin，WU Keqiang，et al. Experiment based modeling of CO₂ solubility in H₂O at 313. 15–473. 15 K and 0. 5–200 MPa[J]. Applied Geochemistry，2021，130：105005.

[22] 杜艺，吕春阳，严世杰，等. 基于原位观测法研究超临界二氧化碳与水影响煤储层矿物和孔裂隙结构的新方法[J]. 天然气工业，2024，44(10)：93−104.

DU Yi，LYU Chunyang，YAN Shijie，et al. A new method for identifying the effect of ScCO₂–H₂O on mineral–pore fracture system of coal reservoirs through in–situ observation[J]. Natural Gas Industry，2024，44(10)：93−104.

[23] 肖晓春，刘海燕，丁鑫，等. 单向卸载条件下组合煤岩力学特性及声发射演化规律[J]. 煤炭科学技术，2023，51(11)：71−83.

XIAO Xiaochun，LIU Haiyan，DING Xin，et al. Mechanical properties and acoustic emission evolution of coal–rock combination under unidirectional unloading condition[J]. Coal Science and Technology，2023，51(11)：71−83.

[24] 葛振龙，孙强，王苗苗，等. 基于RA/AF的高温后砂岩破裂特征识别研究[J]. 煤田地质与勘探，2021，49(2)：176−183.

GE Zhenlong，SUN Qiang，WANG Miaomiao，et al. Fracture feature recognition of sandstone after high temperature based on RA/AF[J]. Coal Geology & Exploration，2021，49(2)：176−183.

[25] 刘鹏，赵渝龙，聂百胜，等. 煤体微观力学特性的纳米压痕实验研究[J]. 煤炭学报，2024，49(8)：3453−3467.

LIU Peng，ZHAO Yulong，NIE Baisheng，et al. Study on nano–mechanical behavior of coal using nanoindentation tests[J]. Journal of China Coal Society，2024，49(8)：3453−3467.

[26] 龚爽，张寒松，赵毅鑫，等. 酸性压裂液对无烟煤动态断裂行为及能量耗散规律影响研究[J]. 岩石力学与工程学报，2024，43(5)：1152−1175.

GONG Shuang，ZHANG Hansong，ZHAO Yixin，et al. Effects of acid fracturing fluid on dynamic fracture behavior and energy dissipation characteristics of anthracite coal[J]. Chinese Journal of Rock Mechanics and Engineering，2024，43(5)：1152−1175.

[27] 马衍坤，李笑笑，翟少彬，等. 含预制钻孔煤体承载破坏应变场与声发射响应真三轴试验[J]. 中国矿业大学学报，2024，53(3)：497−508.

MA Yankun，LI Xiaoxiao，ZHAI Shaobin，et al. The true triaxial test of strain field and acoustic emission response of bearing failure of coal with prefabricated borehole[J]. Journal of China University of Mining & Technology，2024，53(3)：497−508.