Using graphene to simplify the adsorption of methane on shale in MD simulations

doi:10.1016/j.commatsci.2017.03.010

Computational Materials Science

Volume 133, 1 June 2017, Pages 99-107

https://doi.org/10.1016/j.commatsci.2017.03.010 Get rights and content

Highlights

•
The limiting heat of CH₄ adsorption on graphene has been obtained.
•
Adsorption properties of CH₄ on graphene have been clarified.
•
We provide a direct evidence of graphene as a model of shale in simulations.

Abstract

In this paper, we explored material similarity between graphene and shale for methane (CH₄) adsorption in the shale gas recovery simulations. The reasons of choosing graphene to model shale have been clarified. Through theoretical analysis, we obtained the attenuation law of interaction potential between CH₄ and multilayer graphene. It indicates the adsorption energy of CH₄ on monolayer graphene is closest to that on shale. The limiting heat of adsorption of CH₄ on graphene was calculated by molecular dynamics (MD) simulation. The adsorption isotherms and adsorption heats on the monolayer graphene, whose width of the slit pore ranges from 2 nm to 11 nm, were calculated by using grand canonical Monte Carlo (GCMC) simulations at different temperatures. The computed adsorption heat is validated by experimental data, which indicates that the adsorption properties of CH₄ on shale are quite similar with that of CH₄ on graphene. Our study may provide a direct evidence of using graphene in modeling shale in simulating the shale gas adsorption/desorption.

Graphical abstract

Introduction

As a unconventional gas resource, shale gas plays an increasingly important role in renewable energy, because of its great reserves throughout the world and its clean when burned [1], [2]. Most shale gas production in North America attributes to the development of horizontal drilling and fracking technology [3], [4]. Also shale gas has been extensively explored in Australia, Europe and China in recent years [5]. Even though thousands of shale gas wells are in production around the world, there are still many difficulties in shale gas exploitation technology [6], [7], [8], [9], [10], and the thermodynamic properties of shale gas are still poorly understood. Hence, researchers have increasingly tried to explore the properties of shale gas and find out an efficient way in enhancing shale gas recovery (ESGR) [11], [12], [13], [14]. Experiment is a direct way to explore the properties of shale gas in shale [15], [16], [17], [18], [19], but is difficult to achieve high-pressure conditions of methane (CH₄) as the same of real pressure (20–30 MPa) in shale. And most pressure condition in experiment was under 20 MPa [20]. In addition, earlier studies show that shale gas adsorbs in the nanopores [21], [22], [23]. Therefore, it is difficult to experimentally explore the microscopic mechanisms of shale gas adsorption in nanopores. Simulation provides an efficient and inexpensive way to investigate the microscopic properties of CH₄ in shale. However, the components and microstructure of the shale are very complex. For convenience of calculations, we need to find a simple geometry yet similar properties material as a model of shale in the shale gas recovery simulations.

Molecular dynamics (MD) simulations have been extensively conducted to investigate shale gas adsorption. Firoozabadi made a great contribution to the research of hydrocarbons energy production and illuminated the use of thermodynamics in reservoir and transportation of shale gas, and MD simulations were performed in his research [24]. In previous simulations, CH₄ was considered under thermodynamic equilibrium in three-dimensional periodic orthorhombic pore geometry consisting of upper and lower pore-walls made of graphene [25]. Coal and shale both require a thorough understanding of the CO₂ adsorption properties in microporous carbon-based materials. Wilcox et al. investigated the adsorption of CO₂ in microporous carbons. They explored CH₄ adsorption properties on graphitic surfaces as an initial model of coal and kerogen of gas shale [26], [27]. The adsorption behavior of oil within nanoscale carbonaceous slits of shale systems was studied by using MD simulation, with graphene sheets as the model of shale [28]. Recently, the atomic mechanisms and adsorption properties of CH₄ on graphene (or carbon nanopores) have been investigated [29], [30], [31], [32]. Graphene is widely used in the researches of shale and coal. Even though many researchers chose graphene as a model of shale or coal, the reasons for this choice are not clear or the evidence remains insufficient. Hence, material similarity between graphene and shale for CH₄ adsorption need to be explored in detail.

In this paper, thermodynamic properties of the CH₄ adsorption on graphene are investigated and the results are compared with the experiment. Firstly, we used theoretical analysis to investigate the interaction potential between CH₄ and graphene, the effect of the number of graphene layers on the interaction potential was explored. Secondly, we provide a way to calculate the limiting heat of adsorption of CH₄ on graphene, and compared the limiting heat with experimental results. Thirdly, the grand canonical Monte Carlo (GCMC) simulations were performed to predict the CH₄ adsorption isotherm at 300 K, 320 K, 340 K and 360 K, and the fugacity from 1 MPa to 40 MPa, with 2 nm, 3 nm, 5 nm, 7 nm, 9 nm and 11 nm slit pore sizes. And we provide a way to transform fugacity and absolute adsorption into pressure and excess adsorption. Finally, the isoteric adsorption heats of CH₄ in multiple graphene slit pore sizes at different temperatures were investigated. Our results and related analyses may help to understand the CH₄ adsorption on graphene. More importantly, the results provide a strong evidence of using graphene in modeling shale in simulating the shale gas adsorption/desorption. This study aims to quantify whether graphene may be used to represent the wall boundaries of nanopores in shale gas adsorption measurements in MD simulations. It presents future researchers to simplify the description of shale nanostructure with an equivalent slit pore consisting of graphene.

Section snippets

Methods

MD simulations implemented in LAMMPS [33] have been carried out. We simulated the limiting adsorption heat of CH₄ on graphene adopting consistent valence force-field (CVFF) [34], which is based on the ab initio calculations and experiments. The total potential energy consists of the bond energy $E_{b}$ and nonbond energy $E_{ij}$ . $E_{b}$ is the sum of bond and angle energy. $E_{ij}$ is the interaction potential between two atoms i and j, which is Lennard-Jones (LJ) energies: $E_{ij} = 4 ε_{ij} [{(\frac{σ_{ij}}{r_{ij}})}^{12} - {(\frac{σ_{ij}}{r_{ij}})}^{6}],$ where $ε_{ij}$ is

Limiting heat of adsorption of CH₄ on graphene

When the amount adsorbed approaches zero, the isosteric heat of adsorption is called the limiting heat of adsorption. It is a representative thermal effect of the adsorption. The limiting heat of adsorption can be evaluated from Henry constants if they are available for several temperatures, and the Henry constant varies with temperature following the van’t Hoff equation [35]: $\frac{d \ln K}{d T} = \frac{Δ H_{0}}{{RT}^{2}},$ where $K$ is the Henry constant, $T$ is the absolute temperature, $Δ H_{0}$ is the difference of molar enthalpy

Conclusions

For the first time, the interaction potential between multilayer graphene and CH₄ were investigated. The results indicate that the first two layers of graphene play the main role of the interaction potential between multilayer graphene and CH₄. We can just consider investigating the interaction between CH₄ with monolayer graphene (85.5%) or bilayer graphene (96.6%). The limiting heat of CH₄ adsorption on monolayer graphene is 5.97 kcal/mol, and that of CH₄ adsorption on bilayer graphene becomes

Acknowledgments

This research was supported in part by the National Natural Science Foundation of China (NSFC, Grant No. U1562105), and by the Chinese Academy of Sciences (CAS) through CAS Interdisciplinary Innovation Team Project, the CAS Key Research Program of Frontier Sciences (Grant No. QYZDJ-SSW-JSC019) and the CAS Strategic Priority Research Program (Grant No. XDB22040401).

References (40)

C. Mcglade et al.
Unconventional gas – A review of regional and global resource estimates
Energy
(2013)
E. Ghanbari et al.
Impact of rock fabric on water imbibition and salt diffusion in gas shales
Int. J. Coal Geol.
(2015)
R. Heller et al.
Adsorption of methane and carbon dioxide on gas shale and pure mineral samples
J. Unconv. Oil Gas Resour.
(2014)
Y.M. Metwally et al.
Measuring low permeabilities of gas-sands and shales using a pressure transmission technique
Int. J. Rock Mech. Min. Sci.
(2011)
C.R. Clarkson et al.
Pore structure characterization of North American shale gas reservoirs using USANS/SANS, gas adsorption, and mercury intrusion
Fuel
(2013)
P. Chareonsuppanimit et al.
High-pressure adsorption of gases on shales: measurements and modeling
Int. J. Coal Geol.
(2012)
H. Gan et al.
Nature of the porosity in American coals
Fuel
(1972)
K. Mosher et al.
Molecular simulation of methane adsorption in micro-and mesoporous carbons with applications to coal and gas shale systems
Int. J. Coal Geol.
(2013)
S. Wang et al.
Oil adsorption in shale nanopores and its effect on recoverable oil-in-place
Int. J. Coal Geol.
(2015)
K. Lin et al.
Which is the most efficient candidate for the recovery of confined methane: Water, carbon dioxide or nitrogen?
Extreme Mech. Lett.
(2016)

S. Plimpton

Fast parallel algorithms for short-range molecular dynamics

J. Comput. Phys.

(1995)

T. Zhang et al.

Effect of organic-matter type and thermal maturity on methane adsorption in shale-gas systems

Org. Geochem.

(2012)

F. Yang et al.

Fractal characteristics of shales from a shale gas reservoir in the Sichuan Basin, China

Fuel

(2014)

A. Burnham et al.

Life-cycle greenhouse gas emissions of shale gas, natural gas, coal, and petroleum

Environ. Sci. Technol.

(2011)

J.B. Curtis

Fractured shale-gas systems

AAPG Bull.

(2002)

R.W. Howarth et al.

Natural gas: Should fracking stop?

Nature

(2011)

J.D. Hughes

Energy: A reality check on the shale revolution

Nature

(2013)

R. Heller et al.

Experimental investigation of matrix permeability of gas shales

AAPG Bull.

(2014)

A. Al Hinai et al.

Comparisons of pore size distribution: A case from the Western Australian gas shale formations

J. Unconv. Oil Gas Resour.

(2014)

F. Javadpour

Nanopores and apparent permeability of gas flow in mudrocks (shales and siltstone)

J. Can. Pet. Technol.

(2009)

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Using graphene to simplify the adsorption of methane on shale in MD simulations

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Methods

Limiting heat of adsorption of CH4 on graphene

Conclusions

Acknowledgments

Energy

Int. J. Coal Geol.

J. Unconv. Oil Gas Resour.

Int. J. Rock Mech. Min. Sci.

Fuel

Int. J. Coal Geol.

Fuel

Int. J. Coal Geol.

Int. J. Coal Geol.

Extreme Mech. Lett.

J. Comput. Phys.

Org. Geochem.

Fuel

Life-cycle greenhouse gas emissions of shale gas, natural gas, coal, and petroleum

Environ. Sci. Technol.

Fractured shale-gas systems

AAPG Bull.

Natural gas: Should fracking stop?

Nature

Energy: A reality check on the shale revolution

Nature

Experimental investigation of matrix permeability of gas shales

AAPG Bull.

Comparisons of pore size distribution: A case from the Western Australian gas shale formations

J. Unconv. Oil Gas Resour.

Nanopores and apparent permeability of gas flow in mudrocks (shales and siltstone)

J. Can. Pet. Technol.

Limiting heat of adsorption of CH₄ on graphene