龙马溪组页岩干酪根表征初探及干酪根吸附特征研究

doi:10.13809/j.cnki.cn32-1825/te.2023.05.011

Abstract

Abstract:

Adsorbed gas represents a primary mode of shale gas occurrence and is a major source of shale gas production in the later stages of development. It primarily resides within the organic kerogen and clay minerals of shale formations, with organic kerogen being the dominant host. Consequently, the study of organic kerogen characteristics and its adsorption mechanisms is crucial for understanding shale gas development. In this paper, the kerogen of Longmaxi Shale in the Sichuan Basin is taken as the research object. The microstructure of kerogen is expressed by combining methods through the solid-state NMR experiment, Fourier transform infrared spectroscopy experiment, X-ray photoelectron spectroscopy experiment, and the molecular structure model of kerogen is constructed. The adsorption mechanism and characteristics of CH₄ in kerogen of Longmaxi Shale are analyzed by magnetic levitation weight experiment, molecular simulation methods of the Grand Canonical Monte Carlo（GCMC）, and Molecular Dynamics（MD）. The results show that the molecular formula of the kerogen of shale experimental sample of Longmaxi Formation is C₂₃₇H₂₁₉O₂₁N₅S₄. The excess adsorption gas volume of CH₄ in kerogen increase first and then decreased with the increase of pressure. Under the same pore size and pressure, the excess adsorption gas volume and total gas volume of CH₄ decrease with the increase in temperature. The C and S atoms in kerogen are the main cause of CH₄ adsorption. The CH₄ near the kerogen pore wall presents an adsorption state, while the CH₄ far from the kerogen pore wall presents a free state. As the pore size increase, the distance between the two peaks of CH₄ density gradually increases, and the peak value decreases gradually.

Key words: shale kerogen, molecular structure, adsorption characteristics, molecular simulation, Longmaxi Formation

CLC Number:

TE377

HOU Dali, HAN Xin, TANG Hongming, GUO Jianchun, GONG Fengming, SUN Lei, QIANG Xianyu. Primary research on expression of kerogen in Longmaxi Shale and its adsorption characteristics[J].Petroleum Reservoir Evaluation and Development, 2023, 13(5): 636-646.

Figures/Tables 18

Fig. 1

Fig. 2

Fig. 3

Table 1

Table 2

Skeleton parameters of shale kerogen in Longmaxi Formation, Changning area"

骨架参数	物理意义	定义	小数
$f a l$	脂化度	$f a l M + f a l A + f a l B + f a l H + f a l D + f a l O$	0.153 6
$f a r$	芳香度	$f a r A + f a r H + f a r B + f a r C + f a r O$	0.673 6
$X B P$	桥周比	$f a r B / f a r A + f a r H + f a r C + f a r O$	0.160 0
BI	脂肪分支系数	$f a l D + C H - O / f a l$	0.140 0
δ	芳香取代度	$1 - f a r H / f a r$	0.270 0

Table 2

Fig. 4

Fig. 5

Table 3

Fig. 6

Fig. 7

Fig. 8

Fig. 9

Fig. 10

Fig. 11

Fig. 12

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Fig. 14

Fig. 15

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碳官能团	面积分数/%
脂甲基	2.31
芳甲基	1.41
脂C（2）碳	2.90
亚甲基	2.47
次甲基，季sp³碳	0.77
氧—亚甲基	1.37
氧—次甲基	1.43
氧—脂肪环	2.70
氧—芳香环	1.45
质子化芳香碳	48.95
桥联芳香碳	9.13
支链芳香碳	5.36
氧—芳香碳	2.47
羧基，羰基	17.29

元素	归属	结合能/eV	面积分数/%
C1s	C—C，C—H	284.6	55.90
	C—O，C—OH	285.4	20.40
	C=O	287.1	6.60
	O—C=O	288.5	17.10
F1s	F^-	684.4	100.00
N1s	吡啶	398.8	6.50
	吡咯	400.2	64.60
	季氮	401.7	24.50
	氮氧化物	403.0	2.30
S2p	噻吩型硫	162.4	30.16
	亚砜型硫	165.4	33.47
	砜型硫	168.6	36.37

Primary research on expression of kerogen in Longmaxi Shale and its adsorption characteristics

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