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First Thermal and Fluids Engineering Summer Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

Molecular Dynamics Simulation of Methane Adsorption in Shale Matrix

DOI: 10.1615/TFESC1.mnt.013032
pages 1693-1705

Zhong-zhen Li
Key Laboratory of Thermo-Fluid Science and Engineering of MOE School of Energy & Power Engineering Xi'an Jiaotong University

Li Chen
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China; Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA

Ya-Ling He
Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China

Wen-Quan Tao
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China


KEY WORDS: Molecular Dynamics Simulation, Adsorption, Shale Gas, Graphite, Calcite

Abstract

With the increasing demand of natural , shale gains growing attention as a new type of unconventional natural resources. Shale gas is natural gas stored in shale formations in adsorbed, free and dissolved gas form, whose main component is methane. The adsorbed gas is mainly adsorbed on the surface of organics and mineral grains, and the free gas is stored in the slit-pore between the organics and rock grain. The adsorption of methane in the slit-pore has significant effects on the reservoir engineering and transport of shale gas. In order to understand the adsorption mechanism of methane in shale, molecular dynamics simulations of methane adsorption in pores of different solid materials under different pressure and temperature are performed. Results reveal that adsorbed layers are formed near the solid walls due to the adsorption effects of the solid wall, the density of which is higher than that of the free gas region in the middle of the pores where pore pressure is defined. Under relatively low pressures, only one adsorbed layer is observed. As the pressure increases, a second adsorbed layer is gradually formed. When the width of a pore is less than 1.0 nm, methane molecules are always under the influence of adsorption from the pore wall, and adsorption with three density peaks can be observed. The densities in the adsorbed layer and the free gas region achieve constant values if the pore width is wider than a critical value under a certain pressure. Methane is more likely to be adsorbed on the organic matter surface. Besides, the crystal surface of calcite also affects the adsorption.

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