页岩变形干酪根中甲烷吸附-解吸特征分子模拟

doi:10.11743/ogg20250320

Abstract

Abstract:

Current studies on the methane adsorption/desorption behavior in kerogen are primarily conducted based on fixed pore structures. Consequently， the influence patterns and mechanisms of the pore deformation of kerogen on methane adsorption/desorption remain poorly understood. Using molecular simulation， we explore both the methane adsorption/desorption behavior in shale kerogen and the coupled pore deformation characteristics. By constructing and characterizing a nanopore model of kerogen， we investigate the influence of pressure on kerogen deformation. Using a coupling method combining Grand Canonical Monte Carlo （GCMC） and molecular dynamics （also referred to as the GCMC-MD method）， we analyze the coupling characteristics of methane adsorption and kerogen deformation. Additionally， through methane desorption simulation using a kerogen model under high-pressure adsorption equilibrium， we investigate the characteristics and causes of methane desorption hysteresis. The results indicate that ultramicropores in Type ⅡD kerogen serve as the primary migration pathways， while isolated ultramicropores also have the potential to act as migration pathways due to the influence of pore deformation. The pore structures of kerogen generally are reversible during the pressure increase and decrease cycles. The methane adsorption-induced kerogen deformation can be divided into two stages： volume expansion and pore reorganization. The structural deformation of kerogen enhances the methane adsorption capacity， while the selective adsorption of methane onto high-affinity heterogeneous sites in kerogen leads to pronounced changes in pore space. Small desorption hysteresis loops are observed within the deformed structures of kerogen. The methane desorption hysteresis is primarily caused by pore deformation rather than the thermodynamic differences between adsorption and desorption and the capillary condensation effect.

Key words: adsorption, desorption hysteresis, deformation, molecular simulation, kerogen, shale gas

CLC Number:

TE311

Liang HUANG, Zhenyao XU, Qiujie CHEN, Baohua TIAN, Qin YANG, Xinni FENG, Zishuo QU, Zhe YANG, Sirun AN. Molecular simulation of methane adsorption/desorption characteristics of deformed kerogen in shales[J]. Oil & Gas Geology, 2025, 46(3): 995-1005.

Figures/Tables 11

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步骤	系综	温度/K	压力/MPa	密度/（g/cm³）	模拟时间/ps
1	NVT	300	—	0.100	100
2	NVT	300 ~ 1 000	—	0.100	100
3	NVT	1 000	—	0.100	100
4	NPT	700 ~ 1 000	10.0	0.100 ~ 1.130	100
5	NPT	500 ~ 700	10.0	1.130 ~ 1.180	100
6	NPT	300 ~ 500	10.0	1.180 ~ 1.210	100
7	NPT	300	0.1 ~ 10.0	1.210 ~ 1.220	100
8	NPT	300	0.1	1.220 ± 0.004	300

分子类型	原子类型	ε/（kcal/mol）	σ/Å
干酪根	oc	0.240	3.535
	c5	0.064	4.010
	cp	0.064	4.010
	npc	0.134	4.070
	c2	0.054	4.010
	hc	0.020	2.995
	cs	0.064	4.010
	c1	0.054	4.010
	sp	0.071	4.027
	nh	0.134	4.070
	hn	0.013	1.098
	np	0.041	3.570
	c3	0.054	4.010
甲烷	c	0.054	4.010
甲烷	hc	0.020	2.995

压力/MPa	模型体积/Å³	孔隙度/%	孔隙比表面积/（m²/g）
0.10	101 310 ± 206	16.4 ± 0.3	567.1 ± 15.4
10.13	100 911 ± 197	15.9 ± 0.2	545.1 ± 8.2
20.27	100 463 ± 251	15.7 ± 0.4	533.1 ± 18.2
30.40	100 188 ± 218	14.9 ± 0.3	505.8 ± 11.0
20.27	100 373 ± 206	15.2 ± 0.2	512.3 ± 4.4
10.13	100 543 ± 222	15.7 ± 0.3	534.3 ± 14.5
0.10	100 842 ± 373	16.1 ± 0.2	550.9 ± 7.0

压力/MPa	空隙分数/%	空隙比表面积/（m²/g）
0	8.1 ± 0.4	188.7 ± 12.1
0.20	7.6 ± 0.2	177.1 ± 5.2
1.11	5.8 ± 0.3	131.7 ± 9.4
4.15	4.1 ± 0.2	79.6 ± 13.0
7.40	3.6 ± 0.3	70.0 ± 8.9
13.78	2.6 ± 0.1	43.7 ± 15.7
19.05	2.4 ± 0.4	37.5 ± 5.7

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Molecular simulation of methane adsorption/desorption characteristics of deformed kerogen in shales

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