Reconstruction and degradation mechanism of three-dimensional CT cracks in coal under the cycle impact of liquid CO2 high-temperature steam
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摘要: 为解决液态CO2冻结煤层孔隙冰融化时间冗长问题,提出液态CO2−高温蒸汽冷热循环冲击煤层增透技术。本文借助三维CT扫描测试技术,分析冷热循环冲击过程无烟煤三维孔隙结构参数及劣化机理。研究结果表明:① 液态CO2−高温蒸汽冷热循环冲击煤体三维孔隙不断延伸,逐渐形成贯通裂隙,三维孔隙数量、表面积、体积及切片最大面孔率均与冷热循环冲击次数指数相关;② 根据霍多特孔隙分类法,结合等效直径计算公式,发现冷热循环冲击前期渗流孔体积比例增加,三维孔隙劣化表现为裂隙贯通,冷热循环冲击后期吸附孔体积比例增加,三维孔隙劣化表现为煤体内部产生大量新生孔隙。进一步分析得:① 液态CO2−高温蒸汽冷热循环冲击煤体渗流孔半径分形维数增加,孔隙分形特征增强,表面粗糙度提高,热储集性能降低;② 孔隙半径分型模型中lg r随冷热循环冲击次数增加而增加,表明孔径劣化扩张明显;③ 基于冷热循环冲击煤体孔隙力学损伤特征,归纳液态CO2−高温蒸汽冷热循环冲击煤体三维孔隙损伤模型;④ 利用投影法得到切片损伤率,定义液态CO2−高温蒸汽冷热循环冲击煤体三维孔隙损伤量。当冷热循环冲击12次时,三维孔隙损伤量为48.55。Abstract: To solve the problem of long melting time of pore ice in coal seams frozen by liquid CO2, a technology of cold and hot cycling impact on coal seam for penetration enhancement was proposed using liquid CO2 high-temperature steam. This paper used the CT scanning testing technology to analyze the three-dimensional pore structure parameters and degradation mechanism of anthracite under cold and hot cycling impact. The research results indicated that: ① the three-dimensional pores of the coal under the cold and hot cycle impact of liquid CO2 high-temperature steam continued to extend, gradually forming through cracks. The number, surface area, volume, and maximum slice porosity of the three-dimensional pores were all related to the index of cold and hot cycle impact times; ② According to the Hodott pore classification method and the equivalent diameter calculation formula, it was found that in the early stage of cold and hot cycling impact, the proportion of seepage pore volume increased, and the three-dimensional pore degradation manifested as crack penetration. In the later stage of cold and hot cycling impact, the proportion of adsorption pore volume increased, and the three-dimensional pore degradation manifested as the generation of large number of new pores inside the coal. Further analysis shows that: ① the Fractal dimension of seepage pore radius of coal body impacted by liquid CO2 high temperature steam cold and hot cycle increased, the fractal characteristics of pores increased, the surface roughness increased, and the thermal storage performance decreased; ② The lg r in the pore radius classification model increased with the increase of the number of cold and hot cyclic impacts, indicating a significant expansion of pore size degradation; ③ Based on the characteristics of pore mechanical damage in coal under cold and hot cycling impact, a three-dimensional pore damage model of coal under liquid CO2 high-temperature steam cold and hot cycling impact was summarized; ④ The projection method was used to obtain the slice damage rate and define the three-dimensional pore damage amount of coal under the cold and hot cycle impact of liquid CO2 high-temperature water vapor. When subjected to 12 cycles of cold and hot impact, the three-dimensional pore damage was 48.55.
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表 1 煤样工业分析及显微组分分析
Table 1 Industrial analysis and microscopic composition analysis of coal samples
% 煤样 工业分析(质量分数) 显微组分分析(体积分数) Ro,max Mad Aad Vdaf FCad V I E M 无烟煤 0.56 15.88 14.82 68.85 89.20 7.70 0 2.50 2.64 注:Mad为水分;Vdaf为挥发分;Aad为灰分;FCad为固定碳;V为镜质组;I为惰质组;E为壳质组;M为矿物组;Ro,max为镜质组最大反射率。 表 2 液态CO2−高温蒸汽冷热循环冲击煤样孔隙结构参数
Table 2 Pore structure parameters of liquid CO2 high-temperature steam cold and hot cycle impact coal samples
组别 三维孔隙数量/个 A B C D E F 1次CT扫描 107 53 60 430 269 133 2次CT扫描 257 324 125 5064 884 607 3次CT扫描 1660 4294 482 19002 14567 18235 组别 三维孔隙表面积/107 nm2 A B C D E F 1次CT扫描 0.99 0.82 1.54 1.52 2.63 1.26 2次CT扫描 2.58 4.58 6.35 13.16 15.47 27.81 3次CT扫描 7.41 26.08 27.31 56.74 68.62 121.16 组别 三维孔隙体积/108 nm3 A B C D E F 1次CT扫描 3.88 3.52 6.82 3.44 6.46 3.08 2次CT扫描 9.87 20.96 39.06 30.52 58.80 105.18 3次CT扫描 26.21 104.63 231.16 130.15 233.13 491.64 表 3 液态CO2−高温蒸汽冷热循环冲击煤样孔隙损伤率
Table 3 Pore damage rate of coal samples impacted by liquid CO2 high temperature steam cold and hot cycling
组别 三维孔隙损伤率/% A B C D E F 1次CT扫描 1.17 1.32 0.66 2.47 1.29 1.64 2次CT扫描 3.11 4.24 3.52 10.28 8.24 21.15 3次CT扫描 7.99 18.93 12.60 35.19 39.49 79.62 -
[1] 袁亮. 煤及共伴生资源精准开采科学问题与对策[J]. 煤炭学报,2019,44(1):1−9. YUAN Liang. Scientific problem and countermeasure for precision mining of coal and associated resources[J]. Journal of China Coal Society,2019,44(1):1−9.
[2] 周雷,彭雨,卢义玉,等. 基于物质点法的深部煤层气水力割缝卸压解吸增透规律数值模拟研究[J]. 煤炭学报,2022,47(9):3298−3309. ZHOU Lei, PENG Yu, LU Yiyu, et al. Numerical simulation of deep CBM hydraulic slotting pressure relief and desorption and permeability enhancement based on the MPM[J]. Journal of China Coal Society,2022,47(9):3298−3309.
[3] 张永利,刘婷,马玉林,等. 微波辐射煤体孔裂隙结构与渗流特性[J]. 辽宁工程技术大学学报(自然科学版),2022,41(6):481−489. ZHANG Yongli, LIU Ting, MA Yulin, et al. Coal pore and fissure structure and permeability under microwave radiation[J]. Journal of Liaoning Technical University (Natural Science),2022,41(6):481−489.
[4] 林柏泉,钟璐斌,张祥良,等. 高压电脉冲对烟煤微观孔隙结构的影响作用[J]. 采矿与安全工程学报,2022,39(2):380−386. LIN Baiquan, ZHONG Lubin, ZHANG Xiangliang, et al. Effect of high voltage pulse on micro-pore structure of bituminous coal[J]. Journal of Mining & Safety Engineering,2022,39(2):380−386.
[5] 李树刚,王瑞哲,林海飞,等. 超声波功率对煤体损伤特性及能量演化规律的试验研究[J]. 煤炭科学技术,2023,51(1):283−294. LI Shugang, WANG Ruizhe, LIN Haifei, et al. Experimental study on damage characteristics and energy evolution of coal by ultrasonic power[J]. Coal Science and Technology,2023,51(1):283−294.
[6] 楚亚培,张东明,王满,等. 基于核磁共振技术和压汞法的液氮冻融煤体孔隙结构损伤演化规律试验研究[J]. 岩石力学与工程学报,2022,41(9):1820−1831. CHU Yapei, ZHANG Dongming, WANG Man, et al. Experiment study on influence of liquid nitrogen freeze-thaw on pore structure of coal based on nuclear magnetic resonance technology and mercury intrusion methods[J]. Chinese Journal of Rock Mechanics and Engineering,2022,41(9):1820−1831.
[7] 张磊,田苗苗,曾世攀,等. 液氮溶浸对不同煤阶含水煤样渗流特性的影响[J]. 岩土力学,2022,43(11):3015−3026. ZHANG Lei, TIAN Miaomiao, ZENG Shipan, et al. Effect of liquid nitrogen immersion on seepage characteristics of water-bearing coal samples of different coal ranks[J]. Rock and Soil Mechanics,2022,43(11):3015−3026.
[8] 李珍宝,王凤双,梁瑞,等. 液态CO2驱替煤体CH4的渗流特性及机制分析[J]. 采矿与安全工程学报,2022,39(6):1265−1271. LI Zhenbao, WANG Fengshuang, LIANG Rui, et al. Seepage characteristic and mechanism during liquid CO2 displacing CH4 in coal seam[J]. Journal of Mining & Safety Engineering,2022,39(6):1265−1271.
[9] 周西华,周露函,白刚,等. 液态CO2冻融含水煤体孔隙结构演化特性试验研究[J]. 安全与环境学报,2022,22(5):2474−2481. ZHOU Xihua, ZHOU Luhan, BAI Gang, et al. Pore structure of coal with liquid CO2 freeze-thaw saturation[J]. Journal of Safety and Environment,2022,22(5):2474−2481.
[10] ZHANG H T, WANG D K, YU C, et al. Microcrack evolution and permeability enhancement due to thermal shocks in coal[J]. PLoS One,2020,15(5):e0232182. doi: 10.1371/journal.pone.0232182
[11] 王登科,孙刘涛,魏建平. 温度冲击下煤的微观结构变化与断裂机制[J]. 岩土力学,2019,40(2):529−538,548. WANG Dengke, SUN Liutao, WEI Jianping. Microstructure evolution and fracturing mechanism of coal under thermal shock[J]. Rock and Soil Mechanics,2019,40(2):529−538,548.
[12] 王登科,张平,刘淑敏,等. 温度冲击下煤层内部孔缝结构演化特征实验研究[J]. 煤炭学报,2018,43(12):3395−3403. WANG Dengke, ZHANG Ping, LIU Shumin, et al. Experimental study on evolutionary characteristics of pore-fissure structure in coal seam under temperature impact[J]. Journal of China Coal Society,2018,43(12):3395−3403.
[13] 王登科,张平,浦海,等. 温度冲击下煤体裂隙结构演化的显微CT实验研究[J]. 岩石力学与工程学报,2018,37(10):2243−2252. WANG Dengke, ZHANG Ping, PU Hai, et al. Experimental research on cracking process of coal under temperature variation with industrial micro-CT[J]. Chinese Journal of Rock Mechanics and Engineering,2018,37(10):2243−2252.
[14] WANG D K, ZHANG P, WEI J P, et al. The seepage properties and permeability enhancement mechanism in coal under temperature shocks during unloading confining pressures[J]. Journal of Natural Gas Science and Engineering,2020,77:103242. doi: 10.1016/j.jngse.2020.103242
[15] 孙刘涛,王登科,刘淑敏. 温度冲击下煤样渗透率的围压敏感性试验研究[J]. 科学技术与工程,2017,17(29):168−173. SUN Liutao, WANG Dengke, LIU Shumin. Experimental study on the sensitivity of permeability of coal sample under temperature shock and the confining pressure[J]. Science Technology and Engineering,2017,17(29):168−173.
[16] SHEN Y J, HOU X, YUAN J Q, et al. Thermal deterioration of high-temperature granite after cooling shock:multiple-identification and damage mechanism[J]. Bulletin of Engineering Geology and the Environment,2020,79(10):5385−5398. doi: 10.1007/s10064-020-01888-7
[17] 刘淑敏,王登科,尹光志,等. 温度冲击下煤的双胡克体−统计损伤本构模型研究[J]. 采矿与安全工程学报,2019,36(5):1025−1033. LIU Shumin, WANG Dengke, YIN Guangzhi, et al. A double hook-statistical damage constitutive model of coal under temperature impact[J]. Journal of Mining & Safety Engineering,2019,36(5):1025−1033.
[18] 魏建平,孙刘涛,王登科,等. 温度冲击作用下煤的渗透率变化规律与增透机制[J]. 煤炭学报,2017,42(8):1919−1925. WEI Jianping, SUN Liutao, WANG Dengke, et al. Change law of permeability of coal under temperature impact and the mechanism of increasing permeability[J]. Journal of China Coal Society,2017,42(8):1919−1925.
[19] CONG Y Z, ZHAI C, SUN Y, et al. Visualized study on the mechanism of temperature effect on coal during liquid nitrogen cold shock[J]. Applied Thermal Engineering,2021,194:116988. doi: 10.1016/j.applthermaleng.2021.116988
[20] ZHANG L, LU S, ZHANG C, et al. Effect of cyclic hot/cold shock treatment on the permeability characteristics of bituminous coal under different temperature gradients[J]. Journal of Natural Gas Science and Engineering,2020,75:103121. doi: 10.1016/j.jngse.2019.103121
[21] 李和万,王来贵,牛富民,等. 冷热交替作用致煤样裂隙结构损伤试验[J]. 安全与环境学报,2016,16(1):40−43. LI Hewan, WANG Laigui, NIU Fumin, et al. Experimental study on the structure crack damage of the coal samples via the abrupt temperature-changing cycles[J]. Journal of Safety and Environment,2016,16(1):40−43.
[22] XU J Z, ZHAI C, RANJITH P G, et al. Investigation of the mechanical damage of low rank coals under the impacts of cyclical liquid CO2 for coalbed methane recovery[J]. Energy,2022,239:122145. doi: 10.1016/j.energy.2021.122145
[23] 屈晶,申建,韩磊,等. 基于CT图像的高阶煤不同宏观煤岩组分裂隙差异发育规律[J]. 天然气工业,2022,42(6):76−86. QU Jing, SHEN Jian, HAN Lei, et al. Characteristics of fractures in different macro-coal components in high-rank coal based on CT images[J]. Natural Gas Industry,2022,42(6):76−86.
[24] 林海飞,罗荣卫,李博涛,等. 液氮冻融含水煤体孔隙损伤规律实验研究[J]. 西安科技大学学报,2023,43(1):55−64. LIN Haifei, LUO Rongwei, LI Botao, et al. Experimental research on pore damage law of water-contained coal caused by liquid nitrogen freeze-thaw[J]. Journal of Xi’an University of Science and Technology,2023,43(1):55−64.
[25] 黄赞,孙斌,杨青,等. 鸡西盆地煤储层吸附孔特征及分形表征研究[J]. 煤炭科学技术,2021,49(5):218−226. HUANG Zan, SUN Bin, YANG Qing, et al. Study on characterization and fractal features of adsorption pores of coal reservoirs in Jixi Basin[J]. Coal Science and Technology,2021,49(5):218−226.
[26] QIN L, WANG P, LIN H F, et al. Quantitative characterization of the pore volume fractal dimensions for three kinds of liquid nitrogen frozen coal and its enlightenment to coalbed methane exploitation[J]. Energy,2023,263:125741. doi: 10.1016/j.energy.2022.125741
[27] 马玉林,王常瑞,马凯. 红外加热储层煤岩热损伤特征扫描电镜及增透试验研究[J]. 煤炭科学技术,2022,50(7):177−183. MA Yulin, WANG Changrui, MA Kai. SEM and permeability enhancement experiment study on thermal damage characteristics of coal-rock under infrared radiation[J]. Coal Science and Technology,2022,50(7):177−183.