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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
1
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
3
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
4
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
5
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
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