Tackling the challenges in the estimation of methane absolute adsorption in kerogen nanoporous media from molecular and analytical approaches

Pang, Wanying; He, Yanqing; Yan, Chao; Jin, Zhehui

doi:10.1016/j.fuel.2019.01.059

Cited by 37 publications

(55 citation statements)

References 56 publications

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“…Shale reservoirs are typically associated with an organic content from 0.5 wt % to more than 10 wt % . The organic matter (i.e., kerogen) in shale reservoirs contain a considerable number of nano-scale pores. − Type II kerogen is commonly seen in shale media (such as in Bakken formation and Eagle Ford formation). , Type II kerogen can be further divided into four sub-types (types II-A, II-B, II-C, and II-D) from low to high maturity as the atomic O/C and H/C ratios decrease. − On the other hand, during the development of shale reservoirs, there is a massive amount of water existing in the shale formations. The possible water sources include (1) connate water, which typically accounts for 10–30% of the pore volume; , (2) hydraulic fracturing, in which a large amount of water is injected with only a small portion being recovered (e.g., only 7–22% of the injected fluid is recovered in the Marcellus formation); and (3) water alternating gas flooding, in which massive amounts of water is injected into shale formations.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study on CO₂ Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

Zhang

Nan

et al. 2020

Langmuir

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CO2 sequestration in shale reservoirs is an economically viable option to alleviate carbon emission. Kerogen, a major component in the organic matter in shale, is associated with a large number of nanopores, which might be filled with water. However, the CO2 storage mechanism and capacity in water-filled kerogen nanopores are poorly understood. Therefore, in this work, we use molecular dynamics simulation to study the effects of kerogen maturity and pore size on CO2 storage mechanism and capacity in water-filled kerogen nanopores. Type II kerogen with different degrees of maturity (II-A, II-B, II-C, and II-D) is chosen, and three pore sizes (1, 2, and 4 nm) are designed. The results show that CO2 storage mechanisms are different in the 1 nm pore and the larger ones. In 1 nm kerogen pores, water is completely displaced by CO2 due to the strong interactions between kerogen and CO2 as well as among CO2. CO2 storage capacity in 1 nm pores can be up to 1.5 times its bulk phase in a given volume. On the other hand, in 2 and 4 nm pores, while CO2 is dissolved in the middle of the pore (away from the kerogen surface), in the vicinity of the kerogen surface, CO2 can form nano-sized clusters. These CO2 clusters would enhance the overall CO2 storage capacity in the nanopores, while the enhancement becomes less significant as pore size increases. Kerogen maturity has minor influences on CO2 storage capacity. Type II-A (immature) kerogen has the lowest storage capacity because of its high heteroatom surface density, which can form hydrogen bonds with water and reduce the available CO2 storage space. The other three kerogens are comparable in terms of CO2 storage capacity. This work should shed some light on CO2 storage evaluation in shale reservoirs.

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Study on CO₂ Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

Zhang

Nan

et al. 2020

Langmuir

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“…Different adsorption layers are dictated by the local minima in density profiles at high pressures (500 bar) as in our previous work. 32 Therefore, m abs per SA can be obtained based on the adsorbed phase density and volume in each pore, and the expressions in various adsorption types are given as…”

Section: Characterization Of Adsorptionmentioning

confidence: 99%

“…However, a number of molecular simulation works , have shown that ρ a is dependent on pressure, temperature, and pore size. They also showed that CH 4 adsorption behavior is drastically different in micropores and mesopores. − For example, while in micropores (≤2 nm), CH 4 can have a layering structure without the free gas zone, , in mesopores (≥2 nm), the presence of a transition zone beyond the first adsorption layer ,,, can negatively affect m abs calculation. Thus, it is essential to explicitly take into account the pore size distribution (PSD) in shale and the corresponding adsorption behaviors.…”

Section: Introductionmentioning

confidence: 99%

Methane Absolute Adsorption in Kerogen Nanoporous Media with Realistic Continuous Pore Size Distributions

Pang

Jin

2020

Energy Fuels

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Accurate estimation of CH 4 absolute adsorption amount is essential for shale gas-in-place (GIP) evaluation as well as well productivity. Recent studies have shown that pore size distribution (PSD) plays an important role in determination of the absolute adsorption. However, previous studies only contain some discretized pore sizes, while a continuous PSD has not been fully taken into account. In this work, CH 4 adsorption behaviors in various nanopores are first investigated via the grand canonical Monte Carlo (GCMC) simulations. The CH 4 adsorption in nanopores is divided into six distinct adsorption types based on density distributions. Then, the Ono−Kondo (OK) model with PSD lumping is used to characterize CH 4 absolute adsorption in kerogen nanoporous media with pore sizes ranging from 0.7 to 50 nm. The validity of our proposed OK model with PSD lumping is tested by 5 cases with varying micropore volume proportions from 5 to 35%, with each case containing 250 sets of randomly generated PSD samples. We find that by fitting the excess adsorption isotherm, the OK model with PSD lumping has an excellent agreement in terms of the absolute adsorption amounts with those obtained from the GCMC simulation, while deviations increase as micropore volume proportion increases. Overall, the OK model with PSD lumping outperforms the popular single-layered Langmuir and SDR models as well as multilayer models such as supercritical BET (SBET) and single-parameter OK model without PSD considerations for absolute adsorption predictions in kerogen nanoporous media with a continuous PSD.

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“…There have been numerous experimental works to study the gas adsorption behavior in shale media. ,,− Among them, gravimetric and volumetric methods have been widely used to measure the Gibbs adsorption of various hydrocarbon species. ,− However, neither the gravimetric method nor the volumetric method can measure the adsorbed phase volume; therefore, the measured amount of adsorption is the surface excess adsorption. − The surface excess adsorption represents the amount of gas exceeding bulk gas phase density in the system. The absolute adsorption represents the total amount of gas molecules in the sorbed state. − …”

Section: Introductionmentioning

confidence: 99%

Improved Methane Adsorption Model in Shale by Considering Variable Adsorbed Phase Density

Kong¹,

Fan²,

Xiao

et al. 2021

Energy Fuels

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Numerous models have been used to describe the isotherm adsorption of supercritical methane in porous media. Many models assume that the adsorbed phase density does not change with pressure during the adsorption process. However, recent studies show that this assumption is unreasonable, and the resulting error is enormous. Therefore, we propose an improved isotherm adsorption model in shale that assumes that the adsorbed phase density keeps changing and that adsorbed phase volume remains constant during the adsorption process [the variable density adsorption (VD) model]. A logarithmic function is used to describe the change of the adsorbed phase density during the adsorption process. The product of the adsorbed phase density and volume is used to calculate the adsorption capacity. The fitting results for large amounts of methane adsorption data show that this assumption is reasonable. The fitting results are consistent with the molecular simulation, and it will be more convenient to obtain the truly adsorbed phase volume and density. The adsorbed phase volume and density obtained by the VD model show a good positive correlation with the total organic carbon, specific surface area, and micropore volume, which indicates the rationality of adsorption parameters fitted by the model. As a result of the correct calculation of the adsorption phase density, the gas in place (GIP) obtained by the VD model is lower than the supercritical Dubinin–Radushkevich model. The new model proposed this time provides a new tool for the study of shale methane isotherm adsorption and a new model for the calculation of GIP. Using this model, the adsorbed phase density and volume of methane can be obtained more conveniently and accurately. This will be a milestone in the VD model.

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Tackling the challenges in the estimation of methane absolute adsorption in kerogen nanoporous media from molecular and analytical approaches

Cited by 37 publications

References 56 publications

Molecular Dynamics Study on CO₂ Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

Molecular Dynamics Study on CO₂ Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

Methane Absolute Adsorption in Kerogen Nanoporous Media with Realistic Continuous Pore Size Distributions

Improved Methane Adsorption Model in Shale by Considering Variable Adsorbed Phase Density

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Tackling the challenges in the estimation of methane absolute adsorption in kerogen nanoporous media from molecular and analytical approaches

Cited by 37 publications

References 56 publications

Molecular Dynamics Study on CO2 Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

Molecular Dynamics Study on CO2 Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

Methane Absolute Adsorption in Kerogen Nanoporous Media with Realistic Continuous Pore Size Distributions

Improved Methane Adsorption Model in Shale by Considering Variable Adsorbed Phase Density

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Molecular Dynamics Study on CO₂ Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

Molecular Dynamics Study on CO₂ Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size