不同温度下低、中、高阶煤储层甲烷吸附解吸特征差异

doi:10.13809/j.cnki.cn32-1825/te.2020.04.003

Abstract

Abstract:

In order to study the difference in adsorption/desorption characteristics and the desorption hysteresis of CH₄ in different coal ranks, low, medium, and high coal rank samples are collected for the experiments of micro-component determination, liquid nitrogen adsorption, and isothermal adsorption/desorption to systematically analyze the composition, pore structure, differences in adsorption/desorption characteristics and desorption hysteresis effects of different coal rank sample materials. Combined with the calculation results of methane adsorption heat, the mechanism of coalbed methane desorption hysteresis from the energy perspective is discussed. The results show that: ①The reflectance R_o,max of the vitrinite group of coal samples are 0.43 %, 1.26 %, and 3.27 %, respectively. Low-rank coal samples have low vitrinite group content, high inert matter group content, high volatile content and fixed carbon. Medium-rank and high-rank samples are reversed. The degree of coal metamorphism increases. Porosity, BET specific surface area, BJH total pore volume, and fractal dimension D₂ change in a “V” shape, and D₁changes in an inverted “V” shape. ②Under isothermal condition, the residual adsorption amount becomes larger as the coal rank rises, and the desorption becomes more difficult. As the temperature rises, the residual adsorption capacity increases first and then decreases. With 40 ℃ as the inflection point, the temperature influences both the degree of activation of gas molecules and the pore structure of coal. ③When the pressure is the same, the higher the coal rank, the faster the methane adsorption rate at the low-pressure stage（p<4 MPa）, the adsorption capacity increases rapidly at the high-pressure stage（p>4 MPa）, and the adsorption capacity does not increase significantly. ④For the three coal samples, DFS4 ^#, SGZ11 ^#, and SH3 ^#, in the desorption process, their isosteric heat of adsorption are all greater than that in the adsorption process, indicating that the desorption process needs to continuously absorb heat from outside. Therefore, the methane in the adsorption state needs to absorb energy from the external environment, and the energy difference between the adsorption and desorption processes will cause desorption hysteresis. The methane in the free state enters into the micropores due to high pressure, resulting in the expansion and deformation of coal matrix, changes in pore structure, limit of methane desorption, and finally a desorption hysteresis effect.

Key words: metamorphic degree, isothermal adsorption, isobaric adsorption, fractal dimension, adsorption heat, desorption hysteresis

CLC Number:

TE132.2

MA Dongmin,GAO Zheng,CHEN Yue,ZHANG Hui,SHAO Kai,ZHANG Zhicang,WU Xun,YANG Fu. Differences in methane adsorption and desorption characteristics of low, medium and high rank coal reservoirs at different temperatures[J].Reservoir Evaluation and Development, 2020, 10(4): 17-24.

Figures/Tables 14

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References 25

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煤样	煤阶	R_o,max	显微煤岩组分含量
煤样	煤阶	R_o,max	镜质组	惰质组	壳质组	矿物质
DFS4^#煤	CY	0.43	22.8	68.1	2.2	6.9
SGZ11^#煤	JM	1.26	69.8	14.2	0	16.0
SH3^#煤	WY	3.27	61.8	29.6	0	8.6

煤样	煤阶	R_o,max	工业分析
煤样	煤阶	R_o,max	水分（M_ad）	灰分（A_d）	挥发分（V_daf）	固定碳（FC_ad）
DFS4^#煤	CY	0.43	4.65	15.74	32.95	46.66
SGZ11^#煤	JM	1.26	0.96	6.94	16.62	75.48
SH3^#煤	WY	3.27	3.55	13.64	6.38	76.43

煤样	BET比表面积/（m²·g^-1）	各孔径段比表面积比/%			BJH孔容/ （mL·g^-1）	各孔径段孔孔容比/%
煤样	BET比表面积/（m²·g^-1）	<10 nm	10~100 nm	>100 nm	BJH孔容/ （mL·g^-1）	<10 nm	10~100 nm	>100 nm
DFS4^#	11.46	90.51	9.25	0.24	0.019	47.47	43.37	9.16
SGZ11^#	0.34	81.51	17.58	0.91	0.001	30.00	54.00	16.00
SH3^#	2.04	95.30	4.66	0.04	0.002	67.61	26.72	5.67

煤样	A₁	D₁=A₁+3	A₂	D₂=A₂+3
DFS4^#	-0.71	2.29	-0.25	2.75
SGZ11^#	-0.65	2.35	-0.35	2.65
SH3^#	-0.73	2.27	-0.11	2.89

煤样	平衡水含量/ %	温度/ ℃	Langmuir拟合			解吸式拟合
煤样	平衡水含量/ %	温度/ ℃	a_a	b_a	R²	a_d	b_d	c	R²
DFS4^#	10.14	25	11.563	0.448	0.992	8.623	0.701	0.949	0.996
		30	11.566	0.396	0.990	8.341	0.619	0.994	0.997
		35	11.079	0.382	0.993	8.040	0.597	0.973	0.998
		40	10.725	0.374	0.993	7.698	0.543	1.039	0.999
		45	10.238	0.382	0.993	7.380	0.568	1.009	0.998
SGZ11^#	3.01	25	16.370	0.513	0.998	14.130	0.807	0.930	0.995
		30	15.730	0.506	0.998	13.380	0.801	1.020	0.997
		35	15.210	0.493	0.997	12.330	0.795	1.490	0.995
		40	14.730	0.487	0.997	11.720	0.811	1.570	0.993
		45	13.890	0.486	0.999	11.390	0.791	1.210	0.991
SH3^#	4.19	25	37.030	0.430	0.998	29.850	0.721	3.250	0.995
		30	35.240	0.410	0.998	27.860	0.715	3.290	0.992
		35	33.970	0.370	0.997	25.920	0.706	3.340	0.993
		40	32.450	0.340	0.997	23.760	0.695	3.560	0.994
		45	30.910	0.310	0.999	22.320	0.687	3.120	0.996

Differences in methane adsorption and desorption characteristics of low, medium and high rank coal reservoirs at different temperatures

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