The effect of pore size on shale gas recovery with CO2 sequestration

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The effect of pore size on shale gas recovery with CO sequestration: insight into molecular mechanisms Jian Liu, Hui Xie, Qin Wang, Shiyong Chen, and Zhiming Hu

Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04166 • Publication Date (Web): 15 Mar 2019 Downloaded from http://pubs.acs.org on March 21, 2019

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The effect of pore size on shale gas recovery with CO2 sequestration: insight into molecular mechanisms Jian Liu, Hui Xie*, Qin Wang, Shiyong Chen, Zhiming Hu Key Laboratory of Low-Grade Energy Utilization Technologies and Systems of Ministry of Education, College of Power Engineering, Chongqing University, Chongqing 400000, China ABSTRACT: The extremely low permeability of the nanopore causes that only 5%– 15% content of the original shale gas can be extracted and carbon sequestration with enhanced gas recovery (CS-EGR) has been a potentially feasible win-win solution. In this study, the adsorption isotherms, density distributions, the CO2/CH4 adsorption selectivity, the adsorption heat and interaction energies of CH4 and CO2 in the montmorillonite nanopores are calculated and discussed in detail using a series of grand canonical Monte Carlo (GCMC) simulations considering the influence of pore size, temperature and pressure. The recovery of CH4 in montmorillonite nanopores with various size under different injection pressures are also investigated. The results indicate that pore size has significant influence on the adsorption of CH4 and CO2. Under the same conditions, the adsorption capacity of CO2 is obviously stronger than that of CH4 on account of the fact that the interaction energy and the adsorption heat of CO2 are both relatively larger. CO2 and CH4 hold different adsorption sites. CO2 molecules are preferential to accumulate near the Na+ cations. On the contrary, CH4 molecules are under a preference to adsorb in the hollow site of the six-membered oxygen ring in the silicon tetrahedron. Due to the high energy barrier and low diffusion coefficient, CH4 in smaller pores is hard to be displaced and even cannot be extracted in pores with basal spacing corresponding 12 Å even though the pressure increases to 25 MPa. Supercritical CO2 can displace CH4 more quickly and is preferable for CO2 sequestration. We hope this study be beneficial for better understanding of the microscopic states of gas molecules in shale and provide guidance for CS-EGR. 1.

INTRODUCTION Shale gas, as one of the promising unconventional resources with the advantages of

large reserves, low-carbon content and high-energy efficiency, has attracted extensive

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attention1. CO2 is considered to be the main greenhouse gas causing global warming2. Therefore, CS-EGR has been a potentially feasible win-win solution that injects CO2 into deep shale gas reservoirs to enhance gas recovery and sequestrate CO2 at the same time 3-7. Literatures show that shale is the typical nanopore media, including micropores (with pore size smaller than 2 nm) and medium pores (with pore size between 2 and 50 nm) with extremely low permeability and low porosity and the average pore size is 3~5nm 8-11 . It has been estimated that only 5%–15% content of the original shale gas is extracted by gas recovery due to the ultralow permeability 12-13. Therefore, the pore size of shale has key roles in determining the reservoir characteristics and recovery efficiency 8, 14. Organic matter and inorganic clay minerals are the two major components of gas shale matrix 15-16. Basing on previous research17, montmorillonite (MMT) is the most common and widespread mineralogical compositions in the shale formations among the clay minerals. Methane, the main component of shale gas, exists in three forms, namely, free gas, adsorbed gas and dissolved gas in nanometer pores16. Almost 70%– 85% gas stored in the shale matrix is adsorbed gas, which means that adsorbed gas played a critical role in the shale gas resource 12, 18-19. The understanding of fundamental CO2 and CH4 sorption mechanism and the recovery of CH4 within varying pores is beneficial to evaluate and optimize the performance of the enhanced CH4 recovery and to design of CO2 gas injection operation 7. Experiment is a direct way to explore the properties of shale gas in shale, but it is difficult to achieve high-pressure conditions of CH4 as the same of the real pressure in shale

20.

Molecular simulation is an effective means of studying it, due to the small

shale pore size of nanoscale. Zhao et al. explored the recovery dynamics of confined CH4 with H2O, CO2 and N2 by performing molecular dynamics simulations, they found that CO2 is the best choice for CH4 recovery in these three substances and N2 is slightly better than H2O21. Kadoura et al investigated the structural and transport properties of CO2, CH4, and their mixture in hydrated Na-montmorillonite at pre-adsorbed water content and 298.15 K by using molecular dynamics simulations 22. Zhang et al used a series of grand canonical Monte Carlo (GCMC) simulations to research the influence of the pore size on the adsorption of CH4 on the surface of kaolinite23. Yang used the Gibbs ensemble Monte Carlo (GEMC) simulation to study the swelling stability and interlayer structures of montmorillonite-type clay in scCO2 fluid24. Xiong, J., et al used the GCMC and MD methods to investigate the structural and adsorption behaviors of


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CH4 in slit-like quartz nanopores in different pore sizes25. Jiang utilized MD to simulate CH4 adsorption in nanometer graphite channels with various pore sizes19. Liu, Y., et al evaluated CH4 adsorption amount for different pore sizes of the organic shale samples by using simulation method based on the experimental data of pore size distribution 26. Ji et al. conducted methane adsorption experiments on the samples of different particle sizes on the micron scale27. However, the pore size of shale is mainly distributed at the nanometer scale26 and it lacks an explanation of the microscopic mechanism of adsorption. Previous work mainly focuses on the CH4 adsorption amount and the pore size distrubution in the shale but a few researchers investigate the pore size effect on CO2 sequestration and the impact of pore size on shale gas recovery has been neglected. The research on the sorption mechanism and the recovery of CH4 within varying pores is insufficient28. In this work, a series of GCMC simulations are carried out to study the influence of the pore size on the adsorption capacity of CH4 and CO2 on surface of montmorillonite and explain the adsorption mechanism from the perspectives of density distribution, potential energy distribution, adsorption heat and adsorption sites. In addition, the diffusion behavior of gas molecules is researched by using MD method. At last, the recovery of CH4 in different MMT channels with different basal spacings is investigated by conducting hybrid GCMC and MD simulations. 2.

MODELS AND SIMULATION METHOD The model of clay mineral is the sodium-saturated Wyoming-type montmorillonite

22, 29-34

with the chemical formula𝑁𝑎0.75[𝑆𝑖7.75𝐴𝑙0.25](𝐴𝑙3.5𝑀𝑔0.5)𝑂20(𝑂𝐻)4, which

contains tetrahedral and octahedral substitutions. As shown in Figure 1, the simulation cell, with dimensions 21.12, 36.56, and 6.56 Å along x, y, and z directions, is a patch with two tetrahedral-octahedral-tetrahedral (TOT) clay layers24, 34 forming a nanopore. Each layer contains 8 unit cells (2  4  1). The nanopore connects two reservoirs to study the recovery of CH4 from the MMT pore. In this work, we selected four basal spacings d = 12, 18, 30 and 40 Å. The clay model is kept rigid and immobile throughout the simulation processes 22, 24, 35.


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d

Figure 1. The model of montmorillonite slit-nanopore with varying basal spacing. The unattached nanopore is used to study the adsorption properties. When the nanopore is connected to the two reservoirs where the right one is full of CO2 (the injection pressure is controlled by GCMC) and the nanopore is filled with CH4 under different pressure, it is used to study the recovery of CH4 from the MMT pore. The black points at the pore mouth are the “blocker” atoms (a part of the graphene wall). The color scheme: graphene wall (C, gray); MMT( H, white; Al, blue; Si, orange; O, red; Mg, yellow; Na, magenta); CH4, green; CO2 (C, violet); CO2 (O, cyan) . In this work, the CLAYFF36 force field is chosen to describe interactions in the whole simulation. CH4 is represented by a single Lennard-Jones sphere in the TraPPE force field37, and each CO2 molecule is represented by using the flexible force field developed by Cygan et al 38. The potential parameters used in this study are summarized Table 1. The nonbond energy Uij between sites i and j of different particles is defined by the Lennard-Jones (LJ) 12−6 function as follow:   U LJ  rij  =4 ij  ij  rij 

12 6    ij   qi q j         rij   4 0 rij

(1)

where rij denotes the distance of the centers of i and j atoms,  ij and  ij are the LJ potential parameters, q is the electric quantity of the particle, and  0 is the permittivity of the vacuum, respectively. The long-range coulombic interaction is calculated using a particle-particle particle-mesh (PPPM) solver with an accuracy of 10-4. For LJ interaction, a cutoff distance is set to be 9.5 Å. The conventional Lorentz−Berthelot combining rules are utilized to calculate the interaction between different types of atoms. Table 1. Lennard-Jones potential parameters used in this work. Species

ε (Kcal/mol)

σ(Å)

CH4

0.294

3.730

C (CO2)

0.054

2.80

O (CO2)

0.157

3.05

C (graphene)

0.056

3.4

The simulations are divided into two parts: adsorption isotherm simulations and gas 4 ACS Paragon Plus Environment

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recovery simulations. To simulate the adsorption of CH4 and CO2, we carry out the simulation by using the grand canonical Monte Carlo (GCMC) algorithm in the model as shown in Figure 1. In the GCMC simulation, the system achieves equilibration by the exchange, conformation, rotation and translation of molecules with the chemical potential, volume and temperature fixed. Each GCMC simulation run consists of 1 × 106 steps for equilibration and 1 × 107 steps for production with a time step of 1fs. The period boundary condition is applied in three dimensions. The GCMC simulations are performed at the temperature of 298 K, 323 K, 343 K and 373 K with the fugacity of the gas varying from 0.01 MPa to 20 MPa to research the adsorption mechanisms of shale gas in different depth. Then MD simulation method is conducted to calculate the density, potential energy, diffusion properties of CH4 and CO2 in the NVT ensemble with the Nose-Hoover thermostat. Each MD simulation process is carried out over a run time of 2.0 ns, and the last 1.0 ns is used for analysis. To simulate the process of adsorbed CH4 displaced by gas injections, hybrid GCMC and MD simulations are conducted. The simulation model is shown as Figure 1.The dimension of the MMT pore is 21.12 and 146.24 Å along x and y directions. The lengh of the left and right box is 60 Å along y direction. The pressure of the injection gas (CO2) in the right box is controlled by insertion and deletion of gas molecules (performed through GCMC procedure). In this work, a series of pressure of injection gases ranging from 5 MPa to 25 MPa is simulated. The transport behavior of CH4 and CO2 through the MMT is performed by molecular dynamics. Initially, the both sides of the MMT pore is sealed and the configuration that CH4 adsorbed in the MMT pore is obtained from these GCMC adsorption isotherm simulations as shown in Figure 1. The system is equilibrated for 1 ns with shale gas storage pressure (P =3 MPa) in the MMT pore and injection pressure (P =5, 7, 11, 15, 18, 22, 25 MPa, respectively) in the right box. After the equilibrium, the blocker atoms at both sides of the MMT pore are removed. Due to the pressure difference across the MMT pore, gas recovery is initiated. The output gases in the left box is used to compute the physical quantities to study the recovery process. The simulations are conducted in the NVT ensemble at the temperature of 323 K. 3.

RESULTS AND DISCUSSION

3.1 The adsorption isotherms in MMT slit nanopores Figure 2 displays the adsorption isotherms of CH4 and CO2 in different conditions. As shown in Figure 2(a) and (b), the adsorption amount of CH4 and CO2 has the similar 5 ACS Paragon Plus Environment

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changing tendency in general, increasing with the rise of fugacity and decreasing with the increase of temperature. For the same amount, the adsorption heat of CO2 is greater than CH4, which means that the adsorption capacity of CO2 is obviously stronger than that of CH4. Investigating the influence of temperature and pressure on CH4 adsorption, it can be noted that the content of CH4 does not necessarily increase with the fugacity, which increases with the mining depth. In comparison to CH4, the adsorption isotherms of CO2 demonstrate a rapid rise at low-pressure and then reach saturation to a certain extent. The adsorption amount of CH4 and CO2 in the montmorillonite-slit pores of different size is presented in Figure 2(c) and (d). At the same fugacity and temperature, the adsorption amount of CH4 and CO2 increases with the pore size because of the augment in pore volume. In addition, the adsorption amount of CH4 and CO2 in mesopores (18 Å and 12 Å) is significantly less than that in micropores (30 Å and 40 Å). In addition, the adsorption amount of CH4 in mesopores can more easily tend to saturation with the increase of pressure. It indicates that the adsorption amount of CH4 in mesopores is mainly limited by available pore volume and the external condition primarily affects the adsorption process in micropores. As shown in Figure 2(d), the adsorption amount of CO2 increases dramatically at lower fugacity and then reach saturated with fugacity further increasing. These tendencies are consistent with previous studies of organic-rich shales 25, 28, 39. (a)

(b)

(d)

(c)


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Figure 2. The adsorption isotherms of (a) CH4 and (b) CO2 in MMT slit nanopores (d=18 Å) at various temperatures. The adsorption isotherms of (c) CH4 and (d) CO2 for different pore sizes at temperature of 323 K. 3.2 Adsorption Properties of CH4 and CO2 in MMT Slit Nanopores In order to clarify the fact the adsorption amount of CH4 is less than that of CO2, the interaction energy between gas and clay surface is analyzed with varying pressure at the basal spacing of 30 Å and the temperature of 323 K, as shown in Figure 3. The interaction energy between MMT and CO2 contains van der Waals interactions and electrostatic interactions. As regard to CH4, only van der Waals potential energy contributes to the total interaction energy for treated as an uncharged united atom, which demonstrates Van der Waals forces and coulomb forces play different roles for the adsorption of the two species. As illustrated in Figure 3, the interaction energy between the MMT and CO2 is much higher (more negative) than that between the MMT and CH4. Similar conclusions have also been drawn about gas adsorption on clays in previous researches28, 40. Apparently, the interaction energy increases with the rise of pressure due to the fact that the adsorbed gas molecules get closer to the MMT surface with the pressure increasing. The results indicate the interaction energy of CO2 is about four times more than that of CH4, which implies that CO2 adsorbs on MMT more easily than CH4 and can be a good candidate in recovering CH4.


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Figure 3. The interaction energy between the MMT and CH4 or CO2 under different pressures at the temperature of 323 K To investigate the influence of pore size on adsorption and study the adsorption structures, we firstly investigate the gas distribution in the pores with different sizes. Figure 4(a)-(c) illustrate the density and potential profile of CH4 under different pressure gradients in three kinds of different pore size 12 Å, 18 Å and 30 Å, respectively. As shown in Figure 4(a), when the basal spacing is 12 Å, the density distributions of CH4 molecules present relatively narrow peaks in the middle region of pore. The potential energy between the MMT and CH4 molecules presents the pattern of "massive distribution" in the middle plane, which indicates the sorption potential of the pore wall from both sides surface overlaps. With the basal spacing increasing to 18 Å, the sorption potential overlap effect disappears and the density distribution of CH4 molecules shows a transition from one to two separated symmetrical layers, locating close to the clay surface. It is worth noting that the interaction potential in the area near the MMT surface is distinctly stronger with the pattern of "Wavy distribution" and then distributes uniformly near the center, indicating that the adsorbed layers are formed due to the fluid/wall intermolecular interactions41. Figure 4(d) exhibits the density and potential profile of CO2 in the condition that the basal spacing is 30 Å and the temperature is 323 K. Some CH4 and CO2 molecules occur as bulk form at the central region with the increase of basal spacing, in which the potential energy approaches zero. The interaction potentials from each wall disassociate entirely. As the pressure further increases, the adsorption layers of CH4 and CO2 near the pore surface both gradually increase then reach saturation and CH4 and CO2 molecules start to fill in the bulk region, thereby forming two primary peaks and two secondary peaks, even three set of density peaks are observed for CO2 at pressure of 15 and 20 MPa. Noting the critical pressure


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of CO2 is 7.3 MPa and the critical temperature of CO2 is 304.2 K. It can be found that the density of CO2 increases acutely when the state changes from the non-supercritical state to supercritical state when pressure increases. However, a noteworthy detail is that the potential energy of CO2 is much stronger than that of CH4 and they have different distribution approaching to the clay surface. (a)

(b)

(c)

(d)

Figure 4. Density profile and corresponding potential energy distribution of CH4 in MMT channels with different pore sizes (a)12 Å (b)18 Å (c)30 Å and various pressure; (d) Density profile and corresponding potential energy distribution of CO2 with basal spacing of 30 Å under various pressure. (The appended MMT figures are looked from the perspective of Y-Z plane) Furthermore, the interaction energy between the adsorbate and one side of the adsorbent is calculated to research the adsorption site of gas on the adsorbent surface. The results presented in Figure 5 manifest that the energy surface of CH4 and CO2 has shown different distribution characteristics. The interaction energy of CO2 is much stronger than that of CH4. As for CO2, the results in Figure 5(a) and (c) show that the relatively high potential energy occurs at the bridge site of the Si-O bond, especially in the site occupied by Na+. Due to electrostatic forces for the interaction of the polarity on the oxygen atom with the electric quadrupole moment on CO2 molecules42, the sites have a strong attraction to CO2 molecules. It means that CO2 molecules are preferential to accumulate near the Na+ cations. On the contrary, CH4 molecules have a preference 9 ACS Paragon Plus Environment

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to adsorb in the hollow site of the six-membered oxygen ring in the silicon tetrahedron, extrapolated from the potential surface of CH4 in Figure 5(b) and (d), which is in agreement with the adsorption of CH4 and CO2 on the graphite surface studied by Chen et al43. In addition, the adsorption sites of CH4 have been taken up by sodium atoms, leading to the debasement of the interaction energy in these sites. (a)

(c)

(b)

(d)

Figure 5. The potential surfaces of (a) CO2 and (b) CH4 molecules adsorbing on MMT; The potential distribution of (c) CO2 and (d) CH4 molecules proje cted onto the X-Y plane. For the sake of concise, only a fraction of the M MT atoms are shown in the figure. The position of the Na+ is marked with black hexagonal wireframes. The color scheme of atoms: H, white; Al, blue; Si, yellow; O, red; Mg, orange; Na, magenta. 3.3 Competitive Adsorption of CO2 over CH4 in in MMT Slit Nanopores GCMC simulations are also performed on the binary mixtures of an equal molar amount of CO2 and CH4 to analyze the impact of CO2 on the adsorption of CH4 within MMT nanopores. The adsorption isotherms of binary mixtures of CH4 and CO2 in MMT nanopores are shown in Figure 6. Comparing with Figure 2, it can be found that the adsorption tendencies of mixtures of CH4 and CO2 are similar to those of the single 10 ACS Paragon Plus Environment

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components, respectively. (b)

(a)

Figure 6. Adsorption isotherms of binary mixtures of (a) CH4 and (b) CO2 in MMT slit nanopores at various basal spacings with the temperature of 323 K. The density distribution of the binary mixtures of CH4 and CO2 in different pores at the temperature of 323 K with the pressure of

3 MPa is shown in Figure 7. The

layering state, influenced by the interaction between gas and wall molecules, is a typical phonemenon in nanoscale44. It can be observed that the density distribution of CH4 and CO2 has the similar tendency of that in a single component. But the CO2 molecules get closer to the adsorption surface. It also means that CH4 and CO2 are competitively adsorbed to the MMT surface.

Figure 7. The density distribution of the binary mixtures of CH4 and CO2 in different pores at the temperature of 323 K with the pressure of 3 MPa The competitive adsorption of CO2 over CH4 widely exists in MMT nanopores, due to the different adsorption mechanisms. Therefore, the selectivity parameter (S) is introduced to represent the competitive adsorption strength of the binary mixed CH4 and CO2 in MMT nanopores. It is defined as follows： S

xCO2 / xCH 4 yCO2 / yCH4


(2)

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where x is the fraction of gas component in the adsorbed phase, and y is the fraction of gas component in the bulk phase. The adsorption selectivity behaves contrasting for different pore size, as shown in Figure 8. For the MMT channel with basal spacing of 12 Å, the fluctuation may be caused by the anisotropy of the adsorbed surface in the small confined pore. In the relatively larger pore (d≥18 Å) ， the S decreases sharply and approaches a constant value for lack of adsorption sites to capture more gas molecules with the increasing pressure. The S in the small pore (d=12 Å) is larger than that in the larger pores. The former is about one hundred times of the latter. This can be explained by the unique structure of CO2 and CH4. The CO2 molecule with the linear structure can be more easily adsorbed on the clay surface due to the higher potential energy in comparison to the CH4 with the conical structure. With increase of basal spacing, the selectivity goes down due to the difference declining between the affinity of CO2 and CH4 to MMT channel. It can be seen that the adsorption selectivity for CO2/CH4 mixture gas is always greater than one. This indicates that the adsorption capacity of MMT shale for CO2 is greater than that of CH4. It demonstrates that Na-montmorillonite can be considered as promising porous adsorbent to separate CO2 from the production shale gas mixtures. Moreover, this result is also suggested that the clay-based geological formations could be applied for current CO2 sequestration and recovering CH4.

Figure 8. The selectivity varies with pressure in different basal spacings under the temperature of 323 K. For profoundly understanding of the mixture adsorption behavior in the clay pores, we also investigate the isosteric heats(Qst) of the components of the mixture45. Qst is defined as:


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Qst =Rg T 

U ad N ad  U ad N

2 ad

 N ad

N ad 2

(3)

where Uad represents the potential energy of the adsorption phase and Nad is the adsorbed number of gas molecules. < > represents the ensemble average. Figure 9 shows the isosteric heats of adsorption of CO2 and CH4 as a function of the adsorbed amount in the MMT nanopores. The isosteric heats of both CO2 and CH4 decrease with the basal spacings increasing. The Qst value of CO2 is larger than CH4, which further indicates that the CO2 molecule has stronger adsorption capacity compared with CH4. The isosteric heat can reflect the interaction strength between the adsorbate and the adsorbent surface. It can be inferred that the interaction strength in the larger pores (30 Å and 40 Å) is similar and much less than those in the smaller pores (12 Å and 18 Å), extremely in the nanopore of basal spacing corresponding to 12 Å. It is obvious from the Figure 9(a) that the isosteric heats of CO2 decrease at the beginning and then increase with the adsorption loading, causing by the heterogeneous nature of the clay surface. This demonstrates that CO2 molecules first occupy the more energetically favorable sites (near the positive charged sodium ions), and then less favorable sorption sites would be occupied at high adsorption loading. The Qst value of CH4 increases with the adsorption loading. This behavior can be attributed to the fairly homogeneous adsorption feature for nonpolar CH4 in the clay pores, wherein the CH4–clay interaction remains less change during the adsorption process and then the fluid/fluid contribution to the adsorption enthalpy are nonnegligible and play a major role46.

(a)

(b)

Figure 9. The isosteric heats of adsorption of (a) CO2 and (b) CH4 as a function of the adsorbed amount in the MMT channels for different basal spacings. 3.4 The diffusion behavior in MMT slit nanopores In order to reveal the mass transfer mechanism of CH4 and CO2, we investigated the 13 ACS Paragon Plus Environment

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diffusion behavior of CH4 and CO2 in MMT slit nanopores, which is usually described by the diffusion coefficient. The diffusion coefficient is calculated by the Einstein Equation as follow: 1 t  6t

D  lim

N

 r  t   r  0  j 1

j

2

j

(4)

where rj is the position vector of the j gas molecule. Figure 10 illustrates the relationship between diffusion coefficient and pressure in different MMT pores, it can be seen that the diffusion coefficient of CH4 and CO2 increases with the increasing of pore size. The diffusion coefficient of CH4 and CO2 in MMT pore with basal spacing corresponding to 12 Å is obvious two or three orders of magnitude less than that of other pores. The calculated diffusion coefficient of in MMT pore with basal spacing corresponding to 18 Å, 30 Å and 40 Å decreases with pressure and ranges from 10−11 m2/s to 10−9 m2/s, whereas diffusion coefficient of pore with basal spacing corresponding to 12 Å ranges from 10−13 to 10−12 m2/s and has no obvious trend with pressure. It indicates that gas molecules are more difficult to diffuse in small pores. The diffusion coefficient of CO2 is less than that of CH4 under the same condition, which indicates montmorillonite has a stronger adsorption capacity for CO2 comparing with CH4 and it limits the movement of CO2 molecules. (b)

(a)

Figure 10. Variations of diffusion coefficient of (a) CH4 and (b) CO2 as a fun ction of pressure in different MMT pores. 3.5 Recovery of CH4 by CO2 Injection in MMT Nano Pores 3.5.1 The displacement behavior by CO2 injection Figure 11 presents a series of sequential snapshots of displacement process of adsorbed CH4 by the CO2 injection. Initially, the injected CO2 molecules enter the montmorillonite spacing and take up the adsorption sites of CH4 molecules. CH4 molecules are dissociated from the adsorption sites to dissolve into the CO2 phase due 14 ACS Paragon Plus Environment

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to the fact that the adsorption capacity of CO2 is greater than that of CH4. Then some dissolved CH4 molecules are pushed forward by CO2 molecules, and some slip forward on the montmorillonite surface. More and more CH4 molecules gather at the left exit as shown in Figure 11 (b). When the CH4 molecules are driven out of the outlet, the pressure at the outlet suddenly drops and causes cavitation, this phenomenon can be observed in the Figure 11(d). The cavitation volume initially increases over time and then decreases until it disappears. The cavitation technologies can be applied in extraction of oil from oil shale to enhance oil recovery47. The CO2 molecules then gradually fill the montmorillonite channel to reach a steady state.

Figure 11. Snapshots of displacement process of adsorbed CH4 in the MMT nanopore with the basal spacing of 30 Å by the CO2 injection. 3.5.2 Influence of Injection Pressure of CO2 on the Recovery Behavior of CH4 Different equilibrium injection pressure is used to explore the effect of injection pressure on the recovery behavior of CH4. The results are presented in the Figure 12. The initial state of the CH4 storing in nanopores is derived from the equilibrium state with P=3.0 MPa and T=323 K. The mole percentage of CO2 and CH4 in the production gas under different injection pressures are presented in Figure 12(a). These simulation results are qualitatively consistent with the experimental results in the literatures 7, 48-49. From the results presented in Figure 12(a), it is apparent that only CH4 molecules flow 15 ACS Paragon Plus Environment

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out, which is also found in the Figure 11. CO2 breakthrough is defined as the time when CO2 mole percentage in production gas reaches to 3.0%. With the increase of injection pressure, CO2 breakthrough curve become steeper and breakthrough time tends to be shorter in general. As compared to subcritical CO2, supercritical CO2 have lower viscosity, higher diffusion coefficient and stronger permeability. The production gas shows an obviously shorter breakthrough time and changes sharply when injecting supercritical CO2. The breakthrough curves recedes with the injection pressure increasing. (a)

(b)

(d)

(c)

Figure 12. The recovery behavior under different injection pressures in MMT channel with the basal spacing of 30 Å under the temperature of 323 K: (a) breakthrough curves of CO2 and CH4; (b) The change of cumulative amounts of gas with time, (c) the CO2 flux and (d) CO2 sequestration amount. The cumulative amounts of gas recovered and stored in the shale are calculated to estimate the CO2 mass flow rate and the CO2 sequestration capacity. Under different injection pressure, the change of cumulative amounts of gas with time has the similar tendency and Figure 12(b) shows the typical example of pressure 25 MPa. It should be mentioned that the amount of CO2 stored in shale dramatically reaches to a local maximal value and then decreases at the initial state under different pressure, which 16 ACS Paragon Plus Environment

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may be caused by the initial cavitation shock. Then, the amount of CO2 stored in shale increase gradually tending to a constant value and the cumulative number of CO2 in production gas varies almost linearly with time after 1 ns, which manifests that the system has reached steady-state flow. We fit the curve of the cumulative number of CO2 in production gas versus time between 2 and 3 ns to obtain its slope as the CO2 flux, and average the cumulative number of CO2 stored in shale during the steady-state period to obtain CO2 sequestration amount. The results are shown in Figure 12(c) and (d). It can be seen that the CO2 flux increases almost linearly with injection pressure and the CO2 sequestration amount increases sharply and then becomes stable with the injection pressure rising, which has the same tendency with the previous simulation results of adsorption, as shown in Figure 2(b) and (d). The Figure 12(b) illustrates that all of the CH4 molecules inside the MMT channel are quickly replaced by CO2 molecules. The reason for this phenomenon is that the MMT channel has stronger affinity to CO2 than to CH4. Supercritical CO2 can displace CH4 more quickly and is preferable for CO2 sequestration. Zhao et al. found that CO2 is the best choice for CH4 recovery comparing with H2O and N221. Combined with the research results of this work, we can speculate that the supercritical CO2 may be the best candidate for shale gas recovery. 3.5.3 Influence of pore size on the recovery behavior of CH4 Further insight is gained into the pore size influence on the recovery behavior of CH4 and the sequestration of CO2. Figure 13(a) shows the breakthrough curve in different basal spacings under the pressure of 25 MPa and the temperature of 323 K. When the basal spacing of the MMT channel is 12 Å, CH4 molecules are trapped in the middle panel. The channel is too narrow for the entrance of CO2 molecules to recovery the CH4 molecules, only a limited CO2 molecules can squeeze into the channel and stay at the pore opening even the injection pressure increase to 25 MPa. When the pore size increases to18A, the breakthrough curve shows a longer breakthrough time and a gentler front. It indicates a significant size effect on the recovery of CH4 in smaller size. However, the breakthrough curves for the basal spacing corresponding 30 Å and 40 Å are similar and the size effect is not the main factor that affects recovery. To quantify the effect of pore size on the CH4 recovery, the potential of mean forces (PMFs) of CO2 is calculated in these channels at the temperature of 323 K to estimate the energy barriers for CO2 transport. Figure 13(b) shows that the PMF values for CO2 17 ACS Paragon Plus Environment

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in basal spacings decline and then rise when CO2 molecules move from a distance to the center of the MMT channel. The energy barriers in MMT channels with small pore size of 12 Å and 18 Å are 3.19 kcal/mol and 0.54 kcal/mol respectively. Therefore, there are only a limited CO2 molecules at the pore opening in the narrow MMT channel (12 Å) due to the large energy barrier. The energy barriers of MMT channel with basal spacing of 18 Å is not large enough to prevent the CO2 molecules from entering into the MMT channel. The PMF values of the larger pores (30 Å and 40 Å) are similar and below zero, which means that CO2 molecules can spontaneously pass through the MMT channels. The PMF trend confirms the results of simulation for the recovery of CH4. (b)

(a)

Figure 13. (a) Breakthrough curves of CO2 and CH4 in MMT channels with different basal spacings under the pressure of 25 MPa and the temperature of 323 K; (b) The PMF values changes along with the Z-axis of the MMT channel with different basing size. 4.

CONCLUSIONS In this study, the effect of the pore size on the adsorption of CH4, CO2 and their

mixtures in montmorillonite slit nanopores is investigated. The differences of the adsorption mechanism of CH4 and CO2 are analyzed from the perspectives of potential energy distribution, adsorption site and adsorption heat. In addition, the recovery of CH4 from MMT nanopores with disparate basal spacings by injecting CO2 under different injection pressure is studied. According to the analysis and discussions of the results, the following conclusions can be drawn:  Temperature, pressure and pore size have significant influence on the adsorption of CH4 and CO2. Under the same conditions, the adsorption capacity of CO2 is obviously stronger than that of CH4 on account of the fact that the interaction energy between MMT and CO2 and the adsorption heat are 18 ACS Paragon Plus Environment

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both relatively larger.  CO2 and CH4 have different adsorption sites. CO2 is closer to the surface of the montmorillonite. CO2 molecules have a preferential to accumulate near the Na+ cations. On the contrary, CH4 molecules have a preference to adsorb in the hollow site of the six-membered oxygen ring in the silicon tetrahedron.  Due to different pore sizes, potential field overlapping effect exists in montmorillonite, which leads to the different density distributions of CO2 and CH4 in various pore sizes.  CH4 in micropores is hard to be displaced and even cannot be recovered in montmorillonite nanopores with basal spacing corresponding 12 Å even though the pressure increases to 25 MPa. The potential of mean forces in this condition is much larger and CO2 molecules cannot get through the MMT channel because of the high energy barrier and low diffusion coefficient. The injection pressure also has an obvious effect on shale gas recovery. Supercritical CO2 can displace CH4 faster and is preferable for CO2 sequestration. This study reveals the adsorption capacity and adsorption mechanism of CH4 and CO2 in montmorillonite slit nanopores, along with recovery of CH4 by injecting CO2. It should be helpful for better understanding of the microscopic states of gas molecules in shale and might provide guidance for the extraction of shale gas by CS-EGR. AUTHOR INFORMATION Corresponding Author *E-mail:

[email protected]

ORCID Hui Xie: 0000-0002-7179-4843 Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work is supported by the Fundamental Research Funds for the Central Universities (Grant No.2018CDXYDL0001), the National Natural Science Foundation of China (Grant No.51206195) and Natural Science Foundation of ChongQing (Grant No. cstc2013jcyjA90009)..


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Uncategorized References (1).Sun, H.; Zhao, H.; Qi, N.; Li, Y., Molecular Insights into the Enhanced Shale Gas Recovery by Carbon Dioxide in Kerogen Slit Nanopores. Journal of Physical Chemistry C 2017, 121 (18), 10233-10241. (2).Jin, L.; Hawthorne, S.; Sorensen, J.; Pekot, L.; Kurz, B.; Smith, S.; Heebink, L.; Herdegen, V.; Bosshart, N.; Torres, J.; Dalkhaa, C.; Peterson, K.; Gorecki, C.; Steadman, E.; Harju, J., Advancing CO 2 enhanced oil recovery and storage in unconventional oil play—Experimental studies on Bakken shales. Appl Energ 2017, 208, 171-183. (3).Huang, L.; Ning, Z.; Wang, Q.; Ye, H.; Chen, Z.; Sun, Z.; Sun, F.; Qin, H., Enhanced gas recovery by CO2 sequestration in marine shale: a molecular view based on realistic kerogen model. Arab J Geosci 2018, 11 (15). (4).Wan, T.; Liu, H.-X., Exploitation of fractured shale oil resources by cyclic CO2 injection. Petroleum Science 2018, 15 (3), 552-563. (5).Pan, Y.; Hui, D.; Luo, P.; Zhang, Y.; Sun, L.; Wang, K., Experimental Investigation of the Geochemical Interactions between Supercritical CO2 and Shale: Implications for CO2 Storage in Gas-Bearing Shale Formations. Energy & Fuels 2018, 32 (2), 1963-1978. (6).Huang, L.; Ning, Z.; Wang, Q.; Zhang, W.; Cheng, Z.; Wu, X.; Qin, H., Effect of organic type and moisture on CO2/CH4 competitive adsorption in kerogen with implications for CO2 sequestration and enhanced CH4 recovery. Appl Energ 2018, 210, 28-43. (7).Du, X.-D.; Gu, M.; Duan, S.; Xian, X.-F., Investigation of CO2-CH4 Displacement and Transport in Shale for Enhanced Shale Gas Recovery and CO2 Sequestration. Journal of Energy Resources Technology-Transactions of the Asme 2017, 139 (1). (8).Kamari, A.; Li, L.; Sheng, J. J., Effects of rock pore sizes on the PVT properties of oil and gas-condensates in shale and tight reservoirs. Petroleum 2018, 4 (2), 148157. (9).Liang, M.; Wang, Z.; Gao, L.; Li, C.; Li, H., Evolution of pore structure in gas shale related to structural deformation. Fuel 2017, 197, 310-319. (10).Wang, Z. H.; Hu, S. D.; Guo, P.; Meng, W. J.; Ou, Z. P.; Xiao, C.; Qiu, S. F., Molecular simulations of the adsorption of shale gas in organic pores. Mater Res Innov 2015, 19 (sup5), S5-106-S5-111. 20 ACS Paragon Plus Environment

Page 20 of 24

Page 21 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(11).Zhou, J.; Xie, S.; Jiang, Y.; Xian, X.; Liu, Q.; Lu, Z.; Lyu, Q., Influence of Supercritical CO2 Exposure on CH4 and CO2 Adsorption Behaviors of Shale: Implications for CO2 Sequestration. Energy & Fuels 2018, 32 (5), 6073-6089. (12).Huang, X.; Zhao, Y.-P., Characterization of pore structure, gas adsorption, and spontaneous imbibition in shale gas reservoirs. Journal of Petroleum Science and Engineering 2017, 159, 197-204. (13).Wang, S.; Javadpour, F.; Feng, Q., Fast mass transport of oil and supercritical carbon dioxide through organic nanopores in shale. Fuel 2016, 181, 741-758. (14).He, J.; Wang, J.; Yu, Q.; Liu, W.; Ge, X.; Yang, P.; Wang, Z.; Lu, J., Pore structure of shale and its effects on gas storage and transmission capacity in well HD-1 eastern Sichuan Basin, China. Fuel 2018, 226, 709-720. (15).Zhang, H.; Cao, D., Molecular simulation of displacement of shale gas by carbon dioxide at different geological depths. Chemical Engineering Science 2016, 156, 121-127. (16).Pitakbunkate, T.; Blasingame, T. A.; Moridis, G. J.; Balbuena, P. B., Phase Behavior of Methane-Ethane Mixtures in Nanopores. Industrial & Engineering Chemistry Research 2017, 56 (40), 11634-11643. (17).Moucka, F.; Svoboda, M.; Lisal, M., Modelling aqueous solubility of sodium chloride in clays at thermodynamic conditions of hydraulic fracturing by molecular simulations. Physical Chemistry Chemical Physics 2017, 19 (25), 16586-16599. (18).Wang, Z.; Li, Y.; Liu, H.; Zeng, F.; Guo, P.; Jiang, W., Study on the Adsorption, Diffusion and Permeation Selectivity of Shale Gas in Organics. Energies 2017, 10 (1). (19).Jiang, W.; Lin, M., Molecular dynamics investigation of conversion methods for excess adsorption amount of shale gas. Journal of Natural Gas Science and Engineering 2018, 49, 241-249. (20).Lin, K.; Yuan, Q.; Zhao, Y.-P., Using graphene to simplify the adsorption of methane on shale in MD simulations. Computational Materials Science 2017, 133, 99107. (21).Lin, K.; Yuan, Q.; Zhao, Y.-P.; Cheng, C., Which is the most efficient candidate for the recovery of confined methane: Water, carbon dioxide or nitrogen? Extreme Mechanics Letters 2016, 9, 127-138. (22).Kadoura, A.; Narayanan Nair, A. K.; Sun, S., Molecular Dynamics Simulations of Carbon Dioxide, Methane, and Their Mixture in Montmorillonite Clay Hydrates. The Journal of Physical Chemistry C 2016, 120 (23), 12517-12529.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(23).Zhang, B.; Kang, J.; Kang, T., Monte Carlo simulations of methane adsorption on kaolinite as a function of pore size. Journal of Natural Gas Science and Engineering 2018, 49, 410-416. (24).Yang, N.; Yang, X., Molecular simulation of swelling and structure for NaWyoming montmorillonite in supercritical CO2. Molecular Simulation 2011, 37 (13), 1063-1070. (25).Xiong, J.; Liu, K.; Liu, X.; Liang, L.; Zeng, Q., Molecular simulation of methane adsorption in slit-like quartz pores. RSC Advances 2016, 6 (112), 110808-110819. (26).Liu, Y.; Zhu, Y.; Li, W.; Xiang, J.; Wang, Y.; Li, J.; Zeng, F., Molecular simulation of methane adsorption in shale based on grand canonical Monte Carlo method and pore size distribution. Journal of Natural Gas Science and Engineering 2016, 30, 119-126. (27).Ji, W.; Song, Y.; Rui, Z.; Meng, M.; Huang, H., Pore characterization of isolated organic matter from high matured gas shale reservoir. International Journal of Coal Geology 2017, 174, 31-40. (28).Zhang, J.; Clennell, M. B.; Liu, K.; Pervukhina, M.; Chen, G.; Dewhurst, D. N., Methane and Carbon Dioxide Adsorption on Illite. Energy & Fuels 2016, 30 (12), 10643-10652. (29).Lee, M.-S.; McGrail, B. P.; Rousseau, R.; Glezakou, V.-A., Molecular Level Investigation of CH4 and CO2 Adsorption in Hydrated Calcium–Montmorillonite. The Journal of Physical Chemistry C 2017, 122 (2), 1125-1134. (30).Teich-McGoldrick, S. L.; Greathouse, J. A.; Jové-Colón, C. F.; Cygan, R. T., Swelling Properties of Montmorillonite and Beidellite Clay Minerals from Molecular Simulation: Comparison of Temperature, Interlayer Cation, and Charge Location Effects. The Journal of Physical Chemistry C 2015, 119 (36), 20880-20891. (31).Romanov, V. N., Evidence of irreversible CO2 intercalation in montmorillonite. International Journal of Greenhouse Gas Control 2013, 14, 220-226. (32).Rao, Q.; Leng, Y., Methane Aqueous Fluids in Montmorillonite Clay Interlayer under Near-Surface Geological Conditions: A Grand Canonical Monte Carlo and Molecular Dynamics Simulation Study. The Journal of Physical Chemistry B 2014, 118 (37), 10956-10965. (33).Rao, Q.; Leng, Y., Methane aqueous fluids in montmorillonite clay interlayer under near-surface geological conditions: a grand canonical Monte Carlo and molecular dynamics simulation study. J Phys Chem B 2014, 118 (37), 10956-65. (34).Kadoura, A.; Narayanan Nair, A. K.; Sun, S., Adsorption of carbon dioxide, methane, and their mixture by montmorillonite in the presence of water. Microporous 22 ACS Paragon Plus Environment

Page 22 of 24

Page 23 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

and Mesoporous Materials 2016, 225, 331-341. (35).Gadikota, G.; Dazas, B.; Rother, G.; Cheshire, M. C.; Bourg, I. C., Hydrophobic Solvation of Gases (CO2, CH4, H-2, Noble Gases) in Clay Interlayer Nanopores. Journal of Physical Chemistry C 2017, 121 (47), 26539-26550. (36).Cygan, R. T.; Liang, J.-J.; Kalinichev, A. G., Molecular Models of Hydroxide, Oxyhydroxide, and Clay Phases and the Development of a General Force Field. The Journal of Physical Chemistry B 2004, 108 (4), 1255-1266. (37).Siepmann, M. G. M. a. J. I., Transferable Potentials for Phase Equilibria. 1. United-Atom Description of n-Alkanes. Phys. Chem.B 1998, 102, 2569-2577. (38).Cygan, R. T.; Romanov, V. N.; Myshakin, E. M., Molecular Simulation of Carbon Dioxide Capture by Montmorillonite Using an Accurate and Flexible Force Field. The Journal of Physical Chemistry C 2012, 116 (24), 13079-13091. (39).Xiong, J.; Liu, X.-J.; Liang, L.-X.; Zeng, Q., Investigation of methane adsorption on chlorite by grand canonical Monte Carlo simulations. Petroleum Science 2017, 14 (1), 37-49. (40).Jin, Z.; Firoozabadi, A., Methane and carbon dioxide adsorption in clay-like slit pores by Monte Carlo simulations. Fluid Phase Equilibria 2013, 360, 456-465. (41).Yang, S.; Dehghanpour, H.; Binazadeh, M.; Dong, P., A molecular dynamics explanation for fast imbibition of oil in organic tight rocks. Fuel 2017, 190, 409-419. (42).Siriwardane, R. V.; Shen, M.-S.; Fisher, E. P.; Losch, J., Adsorption of CO2 on Zeolites at Moderate Temperatures. Energy & Fuels 2005, 19 (3), 1153-1159. (43).Chen, G.; Lu, S.; Liu, K.; Han, T.; Xu, C.; Xue, Q.; Shen, B.; Guo, Z., GCMC simulations on the adsorption mechanisms of CH 4 and CO 2 in K-illite and their implications for shale gas exploration and development. Fuel 2018, 224, 521-528. (44).Hui, X.; Chao, L., Molecular dynamics simulations of gas flow in nanochannel with a Janus interface. AIP Advances 2012, 2 (4), 042126-042126. (45).Sircar, S.; Mohr, R.; Ristic, C.; Rao, M. B., Isosteric Heat of Adsorption: Theory and Experiment. The Journal of Physical Chemistry B 1999, 103 (31), 65396546. (46).Sui, H.; Yao, J., Effect of surface chemistry for CH 4 /CO 2 adsorption in kerogen: A molecular simulation study. Journal of Natural Gas Science and Engineering 2016, 31, 738-746.


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(47).Avvaru, B.; Venkateswaran, N.; Uppara, P.; Iyengar, S. B.; Katti, S. S., Current knowledge and potential applications of cavitation technologies for the petroleum industry. Ultrason Sonochem 2018, 42, 493-507. (48).Du, X.; Gu, M.; Duan, S.; Xian, X., The Influences of CO2 Injection Pressure on CO2 Dispersion and the Mechanism of CO2-CH4 Displacement in Shale. Journal of Energy Resources Technology 2018, 140 (1). (49).Hadi Mosleh, M.; Sedighi, M.; Vardon, P. J.; Turner, M., Efficiency of Carbon Dioxide Storage and Enhanced Methane Recovery in a High Rank Coal. Energy & Fuels 2017, 31 (12), 13892-13900.


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The effect of pore size on shale gas recovery with CO2 sequestration

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