Pore structure differences between shale and coal and their gas migration mechanisms

被引：0
|
作者：
Deng Z. [1 ,2 ,3 ]
Wang H. [1 ,2 ,3 ]
Jiang Z. [1 ]
Sun M. [4 ]
Wu Z. [4 ]
Xu Y. [4 ]
Ke Y. [1 ,2 ,3 ]
机构：
[1] China University of Petroleum, Beijing, Beijing
[2] PetroChina Research Institute of Petroleum Exploration & Development, Beijing
[3] CNPC Key Laboratory of Unconventional Oil and Gas, Beijing
[4] Northeast Petroleum University, Heilongjiang, Daqing
[5] China Spallation Neutron Source, Guangdong, Dongguan
来源：
Natural Gas Industry | 2022年 / 42卷 / 11期
关键词：
Coal; Fluid-invasion methods; Over-mature shale; Pore connectivity; Pore structure; Small-angle neutron scattering;
D O I：
10.3787/j.issn.1000-0976.2022.11.004
中图分类号：
学科分类号：
摘要：
Shale and coal are unconventional natural gas reservoirs, and their pore structures control the occurrence state and migration mechanism of natural gas. To quantitatively characterize their pore structure characteristics and differences, this paper comparatively analyzes the reservoir capacities and pore structures of the over-mature shale in Lower Silurian Longmaxi Formation and Upper Permian Longtan Formation and the coal in Upper Carboniferous Benxi Formation using small-angle neutron scattering technology (SANS), mercury intrusion capillary pressure method (MICP), gas adsorption method and field emission-scanning electron microscopy, so as to clarify the pore structure differences between shale and coal and their causes. In addition, the occurrence and migration mechanisms of methane in the reservoirs are studied. And the following research results are obtained. First, the main reservoir space in coal is less than 5 nm in pore size, in which methane is mainly in the form of adsorbed gas, while the pores with size larger than 5 nm in shale are the main reservoir space of free gas. Second, the differential characteristics of pore structures based on the experimental results of SANS and MICP can be used to evaluate pore connectivity. In this study, the pore connectivity of coal is better than that of shale. Third, the repeated MICP results indicate that high pressure cannot induce new fractures in the samples of over-mature shale and coal. In conclusion, the desorption of adsorbed gas in micropores of coal reservoirs into free gas is the key to coalbed methane exploitation, and the migration of shale gas from matrix reservoir space to natural or artificial fractures in shale reservoirs is controlled by pore connectivity. What’s more, the key to improving the recovery factor of shale gas is to increase induced fractures in shale, effectively connect induced fractures with natural fractures and improve the connectivity between organic pore networks and the external parts. The research results provide an important theoretical support for subsequent scientific evaluation on these two kinds of unconventional oil and gas reservoirs. © 2022 Natural Gas Industry Journal Agency. All rights reserved.
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页码：37 / 49
页数：12
相关论文
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