3D characterization of pore structure and seepage simulation of tar-rich coal (long flame coal)

doi:10.11949/0438-1157.20220937

Abstract

Abstract:

The three-dimensional characterization of tar-rich coal (long flame coal) was carried out by X-ray CT (computed tomography) imager. An equivalent pore network model (PNM) of the statistical pore size distribution (PSD) is established. The effects of pressure gradient and flow direction on the seepage process are studied. The results show that pores, minerals, and matrix account for 11.30%, 1.03% and 87.67% of the total volume, respectively. The connected porosity is 5.13%. The number of pore equivalent radius within 3—8 μm accounts for 89.23%. The corresponding average coordination number is 2.87, which indicates that the pore connectivity is poor. The number of throats with an equivalent radius less than 2 μm accounts for 73%. The equivalent length of the throat is mainly distributed between 10—30 μm. At the same pressure gradient, three directions of pore pressure, seepage velocity, and flow path distribution are different, showing anisotropy. With the increase of pressure gradient, the seepage velocity increases gradually. The seepage velocity shows an obvious nonlinear relationship with pressure. The harmonic average permeability in three directions is 0.1403 mD, which is close to the measured value (0.1345 mD) of another tar-rich coal in the Yushenfu mining area. The difference is within 5%.

Key words: tar-rich coal, porous media, X-ray imager, 3D characterization, permeability, numerical simulation

摘要：

采用X射线CT(computed tomography)成像仪对富油煤(长焰煤)进行了三维表征，建立了统计孔径分布(PSD)的等效孔隙网络模型(PNM)，研究了压力梯度和流动方向对渗流过程的影响。结果表明：孔隙、矿物和基质分别占总体积的11.30%、1.03%和87.67%，连通孔隙率为5.13%。孔隙等效半径在3~8 μm内的数量占89.23%，平均配位数为2.87，孔隙连通性较差。等效半径小于2 μm的喉道数占73%，喉道的等效长度主要分布在10~30 μm之间。在相同压力梯度下，三个方向的孔隙压力、渗流速度和流动路径分布不同，表现出各向异性。随着压力梯度的增大，渗流速度逐渐增大，且渗流速度随压力的变化呈现明显的非线性关系。三个方向上的调和平均渗透率为0.1403 mD，这与前人测得的榆神府矿区富油煤渗透率(0.1345 mD)相差在5%以内。

关键词: 富油煤, 多孔介质, X射线成像仪, 三维表征, 渗透率, 数值模拟

CLC Number:

TQ 53

Xiaole HUANG, Fu YANG, Lei HAN, Xing NING, Ruiyu LI, Lingxiao DONG, Husheng CAO, Lei DENG, Defu CHE. 3D characterization of pore structure and seepage simulation of tar-rich coal (long flame coal)[J]. CIESC Journal, 2022, 73(11): 5078-5087.

黄笑乐, 杨甫, 韩磊, 宁星, 李瑞宇, 董凌霄, 曹虎生, 邓磊, 车得福. 富油煤（长焰煤）孔隙结构三维表征及渗流模拟[J]. 化工学报, 2022, 73(11): 5078-5087.

Figures/Tables 14

Table 1 Ultimate and proximate analyses of tar-rich coal

元素分析/%						工业分析/%
C_d	H_d	O_d	N_d	S_t,d		FC_ad	M_ad	A_ad	V_ad
81.28	4.42	10.12	0.89	0.52		63.16	6.01	2.60	28.23

Fig.1 Slice results under different filtering methods

Fig.2 REV analysis results

Fig.3 3D digital model of tar-rich coal(a) complete model; (b) pore model; (c) matrix model; (d) mineral model

Table 2 Content of various components in tar-rich coal samples

组分	体积分数/%	各组分体积/μm³	总体积/ μm³	各组分体素	总体素
孔隙	11.30	1731600	15326000	4844250	42875000
矿物质	1.03	157900	15326000	441723	42875000
煤基质	87.67	13437000	15326000	37589000	42875000

Fig.4 Separation and labeling of connected pores(a) connected pores in XY direction; (b) 3D orthogonal slice; (c) volume rendering of connected pores

Fig.5 Equivalent pore network model of tar-rich coal

Fig.6 Pore size distribution (PSD) of PNM(a) pore equivalent radius; (b) pore coordination number; (c) throat equivalent radius; (d) throat length

Table 3 Quantitative parameters of pore network model

参数	孔径/μm	连通孔隙体积/μm³	喉道半径/μm	喉道长度/μm	配位数
最大值	14.09	11727.11	11.04	75.51	16
最小值	2.51	66.49	0.19	6.40	0
平均值	5.80	1058.96	1.63	21.35	2.87

Table 4 Permeability simulation results in different directions

大小	渗流方向	Q/(m³/s)	A/μm²	k_i /mD	平均渗透率/mD
大小	渗流方向	Q/(m³/s)	A/μm²	k_i /mD	几何平均	算术平均	调和平均
50×50×50体素	X	1.3118×10^-10	1259.19	0.1458	0.1422	0.1441	0.1403
	Y	1.0358×10^-10	1259.19	0.1151
	Z	1.5421×10^-10	1259.19	0.1714

Table 5 Basic parameters of simulation

模拟类型

氮气密度

ρ/(kg/m³)

气体动力黏度

μ/(Pa⋅s)

进口压力

P_in/MPa

出口压力

P_out/MPa

Fig.7 Variations of pressure field, velocity field and streamline in three directions during nitrogen seepage

Fig.8 Average seepage velocity of different sections

Fig.9 Variation of seepage velocity under different pressure gradients

References 35

1	王双明, 孙强, 乔军伟, 等. 论煤炭绿色开采的地质保障[J]. 煤炭学报, 2020, 45(1): 8-15.
	Wang S M, Sun Q, Qiao J W, et al. Geological guarantee of coal green mining[J]. Journal of China Coal Society, 2020, 45(1): 8-15.
2	中国石油集团经济技术研究院. 2021年国内外油气行业发展报告[M]. 北京: 石油工业出版社, 2022.
	CNPC Institute of Economic Technology. Report on Domestic and International Oil and Gas Industry in 2021[M]. Beijing: Petroleum Industry Press, 2022.
3	王韶华. 基于低碳经济的我国能源结构优化研究[D]. 哈尔滨: 哈尔滨工程大学, 2013.
	Wang S H. Research on the optimization of China's energy structure based on low-carbon economy[D]. Harbin: Harbin Engineering University, 2013.
4	Yang H, Ma L. Study on distribution law and occurrence characteristics of rich oil in Zichang Mining area[J]. World Scientific Research Journal, 2020,6(1).
5	马丽, 王双明, 段中会, 等. 陕西省富油煤资源潜力及开发建议[J]. 煤田地质与勘探, 2022, 50(2): 1-8.
	Ma L, Wang S M, Duan Z H, et al. Potential of oil-rich coal resources in Shaanxi Province and its new development suggestion[J]. Coal Geology ＆ Exploration, 2022, 50(2): 1-8.
6	Clayton J L, Rice D D, Michael G E. Oil-generating coals of the San Juan Basin, new Mexico and Colorado, USA[J]. Organic Geochemistry, 1991, 17(6): 735-742.
7	Kang Z Q, Zhao Y S, Yang D. Review of oil shale in situ conversion technology[J]. Applied Energy, 2020, 269: 115121.
8	Xin C Y, Lu L, Shi B B, et al. Numerical investigation of local thermal non-equilibrium effects in coal porous media with cryogenic nitrogen injection[J]. International Journal of Thermal Sciences, 2018, 133: 32-40.
9	Wen H, Lu J H, Xiao Y, et al. Temperature dependence of thermal conductivity, diffusion and specific heat capacity for coal and rocks from coalfield[J]. Thermochimica Acta, 2015, 619: 41-47.
10	杨海平, 陈汉平, 鞠付栋, 等. 热解温度对神府煤热解与气化特性的影响[J]. 中国电机工程学报, 2008, 28(8): 40-45.
	Yang H P, Chen H P, Ju F D, et al. Influence of temperature on coal pyrolysis and char gasification[J]. Proceedings of the CSEE, 2008, 28(8): 40-45.
11	周长冰, 万志军, 张源, 等. 气煤热力耦合变形与孔隙演化特征的实验研究[J]. 中南大学学报(自然科学版), 2014, 45(7): 2440-2446.
	Zhou C B, Wan Z J, Zhang Y, et al. Experimental study on coupled thermo-mechanical deformation and pore evolution feature of gas coal[J]. Journal of Central South University (Science and Technology), 2014, 45(7): 2440-2446.
12	Zhao Y X, Sun Y F, Liu S M, et al. Pore structure characterization of coal by NMR cryoporometry[J]. Fuel, 2017, 190: 359-369.
13	Zhang R, Ai T, Li H G, et al. 3D reconstruction method and connectivity rules of fracture networks generated under different mining layouts[J]. International Journal of Mining Science and Technology, 2013, 23(6): 863-871.
14	Fan N, Wang J R, Deng C B, et al. Quantitative characterization of coal microstructure and visualization seepage of macropores using CT-based 3D reconstruction[J]. Journal of Natural Gas Science and Engineering, 2020, 81: 103384.
15	Zhu L Q, Zhang C, Zhang C M, et al. Challenges and prospects of digital core-reconstruction research[J]. Geofluids, 2019, 2019: 7814180.
16	王刚, 杨鑫祥, 张孝强, 等. 基于DTM阈值分割法的孔裂隙煤岩体瓦斯渗流数值模拟[J]. 岩石力学与工程学报, 2016, 35(1): 119-129.
	Wang G, Yang X X, Zhang X Q, et al. Numerical simulation of gas flow in pores and fissures of coal based on segmentation of DTM threshold[J]. Chinese Journal of Rock Mechanics and Engineering, 2016, 35(1): 119-129.
17	Yao Y B, Liu D M, Che Y, et al. Non-destructive characterization of coal samples from China using microfocus X-ray computed tomography[J]. International Journal of Coal Geology, 2009, 80(2): 113-123.
18	Ni X M, Miao J, Lv R S, et al. Quantitative 3D spatial characterization and flow simulation of coal macropores based on μCT technology[J]. Fuel, 2017, 200: 199-207.
19	乔俊程, 曾溅辉, 夏宇轩, 等. 微纳米孔隙网络中天然气充注的三维可视化物理模拟[J]. 石油勘探与开发, 2022, 49(2): 306-318.
	Qiao J C, Zeng J H, Xia Y X, et al. A three dimensional visualized physical simulation for natural gas charging in the micro-nano pore system[J]. Petroleum Exploration and Development, 2022, 49(2): 306-318.
20	Wang G, Shen J N, Liu S M, et al. Three-dimensional modeling and analysis of macro-pore structure of coal using combined X-ray CT imaging and fractal theory[J]. International Journal of Rock Mechanics and Mining Sciences, 2019, 123: 104082.
21	Jing Y, Armstrong R T, Mostaghimi P. Digital coal: generation of fractured cores with microscale features[J]. Fuel, 2017, 207: 93-101.
22	陆韬杰, 胥蕊娜, 姜培学. 基于低场核磁共振的煤粉动态吸附测量[J]. 化工学报, 2020, 71(S2): 195-200.
	Lu T J, Xu R N, Jiang P X. Dynamic adsorption measurement of coal particles based on low field NMR[J]. CIESC Journal, 2020, 71(S2): 195-200.
23	李伟, 要惠芳, 刘鸿福, 等. 基于显微CT的不同煤体结构煤三维孔隙精细表征[J]. 煤炭学报, 2014, 39(6): 1127-1132.
	Li W, Yao H F, Liu H F, et al. Advanced characterization of three-dimensional pores in coals with different coal-body structure by micro-CT[J]. Journal of China Coal Society, 2014, 39(6): 1127-1132.
24	范楠. 煤孔隙结构多尺度表征及其对瓦斯运移特性影响的实验研究[D]. 阜新: 辽宁工程技术大学, 2021.
	Fan N. Experimental study on multi-scale pore structure characterization of coal and its effect on gas migration characteristics[D]. Fuxin: Liaoning Technical University, 2021.
25	焦华喆, 王树飞, 吴爱祥, 等. 膏体浓密床层孔隙结构剪切演化与连通机理[J]. 中南大学学报(自然科学版), 2019, 50(5): 1173-1180.
	Jiao H Z, Wang S F, Wu A X, et al. Shear evolution and connected mechanism of pore structure in thickening bed of paste[J]. Journal of Central South University (Science and Technology), 2019, 50(5): 1173-1180.
26	苗杰. 低渗煤岩大孔隙结构三维重构及渗流模拟[D]. 焦作: 河南理工大学, 2017.
	Miao J. 3D reconstruction and seepage simulation of macropores structure in low permeability coal[D]. Jiaozuo: Henan Polytechnic University, 2017.
27	王刚, 沈俊男, 褚翔宇, 等. 基于CT三维重建的高阶煤孔裂隙结构综合表征和分析[J]. 煤炭学报, 2017, 42(8): 2074-2080.
	Wang G, Shen J N, Chu X Y, et al. Characterization and analysis of pores and fissures of high-rank coal based on CT three-dimensional reconstruction[J]. Journal of China Coal Society, 2017, 42(8): 2074-2080.
28	申艳军, 王旭, 赵春虎, 等. 榆神府矿区富油煤多尺度孔隙结构特征[J]. 煤田地质与勘探, 2021, 49(3): 33-41.
	Shen Y J, Wang X, Zhao C H, et al. Experimental study on multi-scale pore structure characteristics of tar-rich coal in Yushenfu mining area[J]. Coal Geology ＆ Exploration, 2021, 49(3): 33-41.
29	王志国, 冯艳, 杨文哲, 等. 基于REV的孔隙型多孔介质导热分析模型[J]. 化工学报, 2020, 71(S2): 118-126.
	Wang Z G, Feng Y, Yang W Z, et al. Thermal conductivity analysis model of porous media based on REV[J]. CIESC Journal, 2020, 71(S2): 118-126.
30	师庆民, 王双明, 王生全, 等. 神府南部延安组富油煤多源判识规律[J]. 煤炭学报, 2022, 47(5): 2057-2066.
	Shi Q M, Wang S M, Wang S Q, et al. Multi-source identification and internal relationship of tar-rich coal of the Yan'an formation in the south of Shenfu[J]. Journal of China Coal Society, 2022, 47(5): 2057-2066.
31	陈书荣, 王达健, 张雄飞, 等. 多孔介质孔隙结构的网络模型应用[J]. 计算机与应用化学, 2001, 18(S1): 531-535.
	Chen S R, Wang D J, Zhang X F, et al. Applications of network models for pore structure medias[J]. Computers and Applied Chemistry, 2001, 18(S1): 531-535.
32	高慧梅, 姜汉桥, 陈民锋. 多孔介质孔隙网络模型的应用现状[J]. 大庆石油地质与开发, 2007, 26(2): 74-79.
	Gao H M, Jiang H Q, Chen M F. Application on pore network model of porous media[J]. Petroleum Geology ＆ Oilfield Development in Daqing, 2007, 26(2): 74-79.
33	马斌, 马跃征, 史琳. 孔隙特性参数对排驱过程影响的实验研究[J]. 化工学报, 2018, 69(8): 3436-3442.
	Ma B, Ma Y Z, Shi L. Experimental study on pore characters effect on drainage process[J]. CIESC Journal, 2018, 69(8): 3436-3442.
34	尹升华, 王雷鸣, 陈勋, 等. 不同堆体结构下矿岩散体内溶液渗流规律[J]. 中南大学学报(自然科学版), 2018, 49(4): 949-956.
	Yin S H, Wang L M, Chen X, et al. Seepage law of solution inside ore granular under condition of different heap constructions[J]. Journal of Central South University (Science and Technology), 2018, 49(4): 949-956.
35	车禹恒. 基于X-ray μCT扫描的煤孔隙瓦斯微观渗流各向异性特征研究[J]. 矿业安全与环保, 2021, 48(4): 12-17.
	Che Y H. Research on the anisotropic characteristics of gas microscopic seepage in coal pores based on X-ray μCT scanning[J]. Mining Safety ＆ Environmental Protection, 2021, 48(4): 12-17.

[1]	Zhanyu YE, He SHAN, Zhenyuan XU. Performance simulation of paper folding-like evaporator for solar evaporation systems [J]. CIESC Journal, 2023, 74(S1): 132-140.
[2]	Yifei ZHANG, Fangchen LIU, Shuangxing ZHANG, Wenjing DU. Performance analysis of printed circuit heat exchanger for supercritical carbon dioxide [J]. CIESC Journal, 2023, 74(S1): 183-190.
[3]	Zhiguo WANG, Meng XUE, Yushuang DONG, Tianzhen ZHANG, Xiaokai QIN, Qiang HAN. Numerical simulation and analysis of geothermal rock mass heat flow coupling based on fracture roughness characterization method [J]. CIESC Journal, 2023, 74(S1): 223-234.
[4]	Jiahao SONG, Wen WANG. Study on coupling operation characteristics of Stirling engine and high temperature heat pipe [J]. CIESC Journal, 2023, 74(S1): 287-294.
[5]	Siyu ZHANG, Yonggao YIN, Pengqi JIA, Wei YE. Study on seasonal thermal energy storage characteristics of double U-shaped buried pipe group [J]. CIESC Journal, 2023, 74(S1): 295-301.
[6]	Song HE, Qiaomai LIU, Guangshuo XIE, Simin WANG, Juan XIAO. Two-phase flow simulation and surrogate-assisted optimization of gas film drag reduction in high-concentration coal-water slurry pipeline [J]. CIESC Journal, 2023, 74(9): 3766-3774.
[7]	Lei XING, Chunyu MIAO, Minghu JIANG, Lixin ZHAO, Xinya LI. Optimal design and performance analysis of downhole micro gas-liquid hydrocyclone [J]. CIESC Journal, 2023, 74(8): 3394-3406.
[8]	Chen HAN, Youmin SITU, Bin ZHU, Jianliang XU, Xiaolei GUO, Haifeng LIU. Study of reaction and flow characteristics in multi-nozzle pulverized coal gasifier with co-processing of wastewater [J]. CIESC Journal, 2023, 74(8): 3266-3278.
[9]	Xiaosong CHENG, Yonggao YIN, Chunwen CHE. Performance comparison of different working pairs on a liquid desiccant dehumidification system with vacuum regeneration [J]. CIESC Journal, 2023, 74(8): 3494-3501.
[10]	Wenzhu LIU, Heming YUN, Baoxue WANG, Mingzhe HU, Chonglong ZHONG. Research on topology optimization of microchannel based on field synergy and entransy dissipation [J]. CIESC Journal, 2023, 74(8): 3329-3341.
[11]	Rui HONG, Baoqiang YUAN, Wenjing DU. Analysis on mechanism of heat transfer deterioration of supercritical carbon dioxide in vertical upward tube [J]. CIESC Journal, 2023, 74(8): 3309-3319.
[12]	Kexin HUANG, Tong LI, Anqi LI, Mei LIN. Mode decomposition of flow field in T-junction with rotating impeller [J]. CIESC Journal, 2023, 74(7): 2848-2857.
[13]	Fangzhe SHI, Yunhua GAN. Numerical simulation of start-up characteristics and heat transfer performance of ultra-thin heat pipe [J]. CIESC Journal, 2023, 74(7): 2814-2823.
[14]	Jinbo JIANG, Xin PENG, Wenxuan XU, Rixiu MEN, Chang LIU, Xudong PENG. Study on leakage characteristics and parameter influence of pump-out spiral groove oil-gas seal [J]. CIESC Journal, 2023, 74(6): 2538-2554.
[15]	Xingchi ZHU, Zhiyuan GUO, Zhiyong JI, Jing WANG, Panpan ZHANG, Jie LIU, Yingying ZHAO, Junsheng YUAN. Simulation and optimization of selective electrodialysis magnesium and lithium separation process [J]. CIESC Journal, 2023, 74(6): 2477-2485.