Modelling of Adsorption and Diffusion

in Dual-Porosity Materials:

Applications to Shale Gas

Martin Lísal

Institute of Chemical Process Fundamentals, CAS,Prague, Czech Republic

Faculty of Science, J. E. Purkinje University,Ústí n. Lab., Czech Republic

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2

Motivation

shale rocks highly heterogenous systems - challenge to generate realistic

atomistic models of organic and inorganic parts of the shale rocks

engineered (model) materials – zeolites: systematically change the pore sizes,

pore shapes, and pore chemistry - reproduce some of the features of shale

rocks

atomistic models with dual micro/mesoporosities - the roles played by each

porosity scale and the underlying links between the two porosity networks on

the adsorption and diffusion of confined fluids

Atomistic Simulations to Provide Insights into

Adsorption and Diffusion of Fluids in Shale Rocks

Organic Matter Zeolite

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Shale RocksSEM Micrograph of Shale Rock

shale rocks comprised of two distinct parts

• organic matter

• clay minerals (inorganic part)

shale gas (a mixture of C1, C2 and C3 with a

small amount of C4, heavier HCs, CO2 and N2)

• free gas

• adsorbed gas

• dissolved gas

shale gas primarily adsorbed in organic matter

atomistic modelling

• simulation domain, max up to

10 nm x 10 nm x 10 nm

• divide-and-conquer approach

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Outline of the Talk

atomistic models for organic matter & engineered materials

atomistic models for shale gas & simulation methods

adsorption and diffusion in the engineered materials

adsorption and diffusion in organic matter

conclusion

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Atomistic models of organic matter

* * Postmature Type II Kerogen1

(gas formation zone)

Kerogen van Krevelen Diagram * Mature Type II Kerogen1

(oil formation zone)

1P. Ungerer et al., Energy Fuels 29, 91, 2015.

• Type I: lacustrine

• Type II: marine

• Type III: terrestrial

• Type IV: originated

from residues

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Atomistic models of organic matter (cont.)asphaltene/resin

fragment

1B. P. Tissot and D. H. Welte, Petroleum Formation and Occurrence (Springer: Berlin, 1984).2J. Collel et al., Energy Fuels 28, 7457, 2014.3P. Dauber-Osguthorpe et al., Protein Struct. Funct. Genet. 4, 31, 1988; M. J. Robertson et al.,

J. Chem. Theory Comput. 11, 3499, 2015.4L. Michalec and ML, Molec. Phys. 115, 1086, 2017.

Composition1,2:

• kerogen fragments

• asphaltene/resin fragments

• heavy HCs (C14, toluene, dimethylnapthalene)

• dissolved gas (C1, C2, C3, C4, C8)

• residual compounds (H2O, CO2)

Consistent Valence FF (CVFF) & OPLS-AA3

microporous structures generated by the compression-cooling protocol4

copying the microporous structures and introducing a slit-like mesopore

Dual-Porosity Proxy Models for Type II OMs

[microporosity (<2nm) & mesoporosity (>2nm)]

Postmature OM

mesoporosity

microporosity

Atomistic models of organic matter (cont.)

microporosity

mesoporosity

Mature OM

micropores microporesmesopores mesopores

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Atomistic models of engineered material HIPC: Na+ zeolites ZSM-5/35 (Si/Al=35)

MFI unit cell (http://www.iza-structure.org/databases) duplicated in the x-, y- and z-directions

random replacement of Si by Al under Löwenstein’s rule constrain (avoid -Al-O-Al-); charge neutrality by

insertion Na+ cations; rigid framework

Vujic-Lyuabartsev’s force field, Modelling Simul. Mater. Sci. Eng. 24, 045002, 2016; atoms as charged LJ

spheres (vdW and electrostatics interactions)

Microporous ZSM-5/35Dual Micro/Mesoporous

ZSM-5/35

Dmicro=0.54 nm

Vmicro=0.172 cm3/g

SA=257 m2/g

Vmicro=0.193 cm3/g

Vmeso=0.115 cm3/g

SA=440 m2/g4 nm

mesopore

E. Rezlerová et al., Langmuir 33, 11126, 2017

Atomistic models for shale gas

united-atom and all-atom models

Transferable Potentials for Phase Equilibria (TraPPE)1

All-Atom Optimised Potentials for Liquid Simulations (OPLS-AA)2CH4

united atom1M. G. Martin and J. I. Siepmann, J. Phys. Chem. B 102, 2569, 1998.2M. J. Robertson et al., J. Chem. Theory Comput. 11, 3499, 2015.

methane

all atoms

Simulation methods Grand Canonical Monte Carlo

reservoir porous phase

• equilibrium number of adsorbed molecules,

adsorption isotherms

Equilibrium Molecular Dynamics

• density distributions

• self-diffusivity via mean squared displacements (MSDs)

Nonequilibrium Molecular Dynamics

• collective diffusivity

• transport diffusivityE. Rezlerová et al., Langmuir 33, 11126, 2017

Zeolites: Molecular model validation

excellent agreement between GCMC simulations and HIPC’s measurement

Type I isotherms

ZSM-5/35 has a higher affinity towards C2H6 than towards CH4

E. Rezlerová et al., Langmuir 33, 11126, 2017

CH4 @ 293 Kmicroporous ZSM-5/35

C2H6 @ 293 Kmicroporous ZSM-5/35

Adsorption Isotherms

Zeolites: Adsorption isotherms

CH4 @ 293 K

CH4 and C2H6 Type I isotherms; C3H8 and C4H10 Type I isotherms in microporous ZSM-5/35 but

Type II in dual-porosity ZSM-5/35

CH4: n(microporous) > n(mesoporous)

C2H6, C3H8 and C4H10: crossover P; n(microporous) > n(mesoporous) below the crossover P and

n(mesoporous) > n(microporous) above the crossover P

C2H6 @ 293 KC3H8 @ 293 K

E. Rezlerová et al., Langmuir 33, 11126, 2017

Zeolites: Density profiles in mesopore

CH4: homogeneous fluid structure; C2H6, C3H8 and C4H10 preferential adsorption at the

mesopore surface

increasing P: both the preferential adsorption and density away from the mesopore surface

increase

4 nmmesopore

293 K, 2 bar 293 K, 7 bar

E. Rezlerová et al., Langmuir 33, 11126, 2017

Zeolites: Self-diffusivity

MFI framework: 3D channel structure

0.54 nm x 0.56 nm straight channels in the y-direction

0.56 nm zigzag channels in the x-direction

tortuous connections through straight-zigzag channel intersections

in the z-direction

y-diffusion > x-diffusion > z-diffusion

mesopore along the y-direction

Microporous ZSM-5/35

Dual Micro/Mesoporous

ZSM-5/35

E. Rezlerová et al., Langmuir 33, 11126, 2017

Zeolites: Self-diffusivity (cont.)

,

microporous ZSM-5/35: self-diffusivity decreases with P

dual-porosity ZSM-5/35: self-diffusivity in the x- and z-directions decreases with P while

self-diffusivity in the y-direction increases with P

1 to 2 order increase of the self-diffusivity in the dual-porosity ZSM-5/35 wrt the

microporous ZSM-5/35

CH4 @ 293 Ky(d-p)

y(micro)

x(micro)

x(d-p)

z(d-p)

z(micro)

C2H6 @ 293 Ky(d-p)

y(micro)

x(d-p)

x(micro)

z(d-p)

z(micro)

E. Rezlerová et al., Langmuir 33, 11126, 2017

Organic Matter: Methane adsorption

Mature OM Postmature OM

Adsorption Isotherms Adsorption Isotherms

postmature OMs a higher affinity to C1 than mature OMs

adsorption isotherms decrease with T and increase with P

mature OM: maximum in excess adsorption isotherm @ 298 K

Organic Matter: Methane adsorption (cont.)

Mature OM: T=365 KMature OM: T=365 K, P=275 bar

Density Profiles

Adsorption Isotherm

mesoporous regions: ~2/3 C1 adsorption

free volume of mesoporous regions: 1/2 adsorption

Organic Matter: Methane self-diffusivity

Self-Diffusivity Self-Diffusivity

Mature OM w/ a Larger 3.5nm Mesopore

pronounced increase of self-diffusivity due to the larger mesopore, depending on T

decrease of self-diffusivity with P and increase of self-diffusivity with T

unusual T-dependence for the system with the smaller mesopore @ 365 K

Mature OM w/ a Smaller 2.5nm Mesopore

Organic Matter: Methane self-diffusivity (cont.)

Mature OM: T=365 K

In-Plane Mean Squared Displacement

Self-Diffusivity

Mature OM: T=365 K, P=275 bar

overall self-diffusivity as well as self-diffusivities in the microporous and mesoporous regions

decrease with P

microporous region: self-diffusivity ~1/2 of the overall self-diffusivity

mesoporous region: self-diffusivity ~1/3 higher than the overall self-diffusivity

Conclusion

Acknowledgment

Lukáš Michalec, Eliška Rezlerová, Michal Řeřicha

ShaleXenvironmenT

cooling-compression strategy to construct proxy models of

dense porous organic matters

effect of T & P on interplay between alkane adsorption and

diffusion

roles play by microporosity and mesoporosity on alkane

adsorption and diffusion