Organic Matter of Shale: Insight from Atomistic …...Adsorption amount of carbon dioxide in the...
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Organic Matter of Shale: Insight from Atomistic Simulations Motivation Lukas Michalec and Martin Lísal 1,2 1,2 Laboratory of Aerosols Chemistry and Physics, Institute of Chemical Process Fundamentals of the CAS, v. v. i., Prague, Czech Republic Department of Physics, Faculty of Science, J. E. Purkinje University, Ústí n. Labem, Czech Republic 1 2 C 175 H 102 O 9 N 4 S 2 We acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640979. P T MD in the -direction ( = x,y,z) adsorption amount from the gas and density profiles Adsorption Modelling Van Krevelen diagram and overmature type II kerogen studied C 2 H 6 C 1 H 4 C 3 H 8 CO 2 Abstract We use all-atom molecular dynamics (MD) simulations to generate porous structures of type II kerogen with control microporosity. The structures mimic organic part of Barnett shale under typical reservoir conditions of 365K and 275bar. First, we built an atomistic model of a kerogen unit using the Consistent Valence Forcefield (CVFF) and structure proposed by Ungerer et al. [1]. Second, we generate various dense kerogen structures by gradual cooling and compression of initial low-density random configurations of kerogen units. During the structure generation, we use a dummy Lennard-Jones (LJ) particle of varying size to introduce control microporosity into the kerogen structures. We systematically characterise the porous kerogen structures by calculating e.g. the pore limiting diameter and geometric pore size distribution, and by analysing the structure connectivity and percolation of the porous space [2]. Finally, we employ Grand Canonical Monte Carlo (MC) and MD of gas-kerogen structure-gas systems and study the adsorption of pure methane, shale gas and carbon dioxide in the generated kerogen structures. Due to rising prices of crude oil, shale gas becomes one of the most important candidate among unconventional sources of energy. One of the major issues in the extraction of shale gas is prediction of estimating gas content in the reservoir. Gas is stored in small free spaces in rocks or is adsorbed onto organic matter and clay. Kerogen is the most abundant part of the organic matter in the sedimentary rock. Kerogen differs by origin and maturity level and it is commonly classified using the Van Krevelen diagram. Porous Kerogen Structures Molecular model of Type II kerogen unit studied. The model was built based on the experimental elemental and functional analyses [1] using the CVFF Structure Generation Time variation of temperature and system density during generation of kerogen structures Kerogen structures were generated by a step-wise cooling and compression of a low-density random configuration of 12 kerogen units and a dummy LJ particle of size {0, 9, 11, 13}Å from 900K to 365K and 275bar using MD simulations. This was followed by heating to 2000K and a subsequent slow cooling to 365K and 275bar which led to a structure refinement. The dummy LJ particle introduced a microporosity into the kerogen structures. Example of generated kerogen structure with a dummy LJ particle Accessible surface in the kerogen structure Density [g/cm 3 ] Particle size [Å] 0 9 11 13 1.296 1.284 1.259 1.241 Maximum pore diameter [Å] 5.02 7.68 9.15 11.55 Density and maximum pore diameter of the generated kerogen structures; experimental density of overmature shale kerogen is between 1.2 and 1.4g/cm 3 pure methane; OPLS forcefield [3] shale gas: 82% methane/12% ethane/6% propane; OPLS forcefield [3] carbon dioxide; EPM2 forcefield [4] Grand Canonical MC μ i bulk = μ i kerogen at fixed T and V μ i bulk by configurational-bias Widom's insertion during NPT MC MD of Gas-Kerogen Structure-Gas Systems Example of simulation box with two copies of generated kerogen structure for adsorption of methane Density profiles of methane and kerogen Models of gas molecules studied References Results Adsorption amount of pure methane in the kerogen structures at 365K and 275bar Adsorption amount of shale gas in the kerogen structures at 365K and 275bar Adsorption amount of carbon dioxide in the kerogen structures at 365K and 275bar . [1] P. Ungerer, J. Collell, M. Yiannourakou: Molecular Modeling of the Volumetric and Thermodynamic Properties of Kerogen: Influence of Organic Type and Maturity. Energy Fuels, 2015, 29: 91−105. [2] L. Sarkisov, A. Harrison: Computational Structure Characterisation Tools in Application to Ordered and Disordered Porous Materials. Molec. Simul. 2011, 37: 1248-1257. [3] W. L. Jorgensen, D. S. Maxwell, J. Tirado-Rives: Development and Testing of the OPLS All-Atom Force Field on Conformational Energetics and Properties of Organic Liquids. J. Am. Chem. Soc. 1996, 118: 11225–11236. [4] G. J. Harris, H. K. Yung: Carbon Dioxide's Liquid-Vapor Coexistence Curve and Critical Properties As Predicted by a Simple Molecular Model. J. Phys. Chem. 1995, 99: 12021–12024. used kerogen Structure Characterisation Pore size distributions of the generated kerogen structures Pore Size Distribution Structure Generation Kerogen Unit
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Organic Matter of Shale: Insight from Atomistic Simulations
Motivation
Lukas Michalec and Martin Lísal 1,2 1,2
Laboratory of Aerosols Chemistry and Physics, Institute of Chemical Process Fundamentals of the CAS,
v. v. i., Prague, Czech Republic
Department of Physics, Faculty of Science, J. E. Purkinje University,
Ústí n. Labem, Czech Republic
1 2
C175H102O9N4S2
We acknowledge funding from the European Union’s Horizon 2020 research and innovation programmeunder grant agreement No 640979.
P T MD in the -direction ( = x,y,z)adsorption amount from the gas and density profiles
Adsorption Modelling
Van Krevelen diagram and overmature type II kerogen studied
C2H6C1H4 C3H8 CO2
Abstract
We use all-atom molecular dynamics (MD) simulations to generate porous structures of type II kerogen with control microporosity. The structures mimic organic part of Barnett shale under typical reservoir conditions of 365K and 275bar. First, we built an atomistic model of a kerogen unit using the Consistent Valence Forcefield (CVFF) and structure proposed by Ungerer et al. [1]. Second, we generate various dense kerogen structures by gradual cooling and compression of initial low-density random configurations of kerogen units. During the structure generation, we use a dummy Lennard-Jones (LJ) particle of varying size to introduce control microporosity into the kerogen structures. We systematically characterise the porous kerogen structures by calculating e.g. the pore limiting diameter and geometric pore size distribution, and by analysing the structure connectivity and percolation of the porous space [2]. Finally, we employ Grand Canonical Monte Carlo (MC) and MD of gas-kerogen structure-gas systems and study the adsorption of pure methane, shale gas and carbon dioxide in the generated kerogen structures.
Due to rising prices of crude oil, shale gas becomes one of the most important candidate among unconventional sources of energy. One of the major issues in the extraction of shale gas is prediction of estimating gas content in the reservoir. Gas is stored in small free spaces in rocks or is adsorbed onto organic matter and clay. Kerogen is the most abundant part of the organic matter in the sedimentary rock. Kerogen differs by origin and maturity level and it is commonly classified using the Van Krevelen diagram.
Porous Kerogen Structures
Molecular model of Type II kerogen unit studied. The modelwas built based on the experimental elemental and functionalanalyses [1] using the CVFF
Structure Generation
Time variation of temperature and system density during generation of kerogen structures
Kerogen structures were generated by a step-wise cooling and compression of a low-density random configuration of 12 kerogen units and a dummy LJ particle of size {0, 9, 11, 13}Å from 900K to 365K and 275bar using MD simulations. This was followed by heating to 2000K and a subsequent slow cooling to 365K and 275bar which led to a structure refinement. The dummy LJ particle introduced a microporosity into the kerogen structures.
Example of generated kerogenstructure with a dummy LJ particle
Accessible surface in the kerogenstructure
Density [g/cm3]Particle size [Å]
0
9
11
13
1.296
1.284
1.259
1.241
Maximum pore diameter [Å]
5.02
7.68
9.15
11.55
Density and maximum pore diameter of the generated kerogen structures; experimental density of overmature shale kerogen is between 1.2 and 1.4g/cm3
pure methane; OPLS forcefield [3]shale gas: 82% methane/12% ethane/6% propane; OPLS forcefield [3]carbon dioxide; EPM2 forcefield [4]
Grand Canonical MC
μibulk = μi
kerogen at fixed T and Vμi
bulk by configurational-bias Widom's insertion during NPT MC
MD of Gas-Kerogen Structure-Gas Systems
Example of simulation box with two copies of generated kerogenstructure for adsorption of methane
Density profiles of methane and kerogen
Models of gas molecules studied
References
Results
Adsorption amount of pure methane in the kerogenstructures at 365K and 275bar
Adsorption amount of shale gas in the kerogen structuresat 365K and 275bar
Adsorption amount of carbon dioxide in the kerogenstructures at 365K and 275bar
.
[1] P. Ungerer, J. Collell, M. Yiannourakou: MolecularModeling of the Volumetric and Thermodynamic Propertiesof Kerogen: Influence of Organic Type and Maturity. EnergyFuels, 2015, 29: 91−105.
[2] L. Sarkisov, A. Harrison: Computational StructureCharacterisation Tools in Application to Ordered andDisordered Porous Materials. Molec. Simul.2011, 37: 1248-1257.
[3] W. L. Jorgensen, D. S. Maxwell, J. Tirado-Rives: Development and Testing of the OPLS All-Atom Force Fieldon Conformational Energetics and Properties of OrganicLiquids. J. Am. Chem. Soc. 1996, 118: 11225–11236.
[4] G. J. Harris, H. K. Yung: Carbon Dioxide's Liquid-Vapor Coexistence Curve and Critical Properties As Predicted by aSimple Molecular Model. J. Phys. Chem. 1995, 99:12021–12024.
used kerogen
Structure Characterisation
Pore size distributions of the generated kerogen structures
Pore
Siz
e D
istr
ibut
ion
Structure Generation
Kerogen Unit
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