Supercritical Methane Adsorption Research Articles

Determining Supercritical Methane Adsorption Phase Density in Nanoscale Shale: from Polanyi Theory to Machine Learning

Determining Supercritical Methane Adsorption Phase Density in Nanoscale Shale: from Polanyi Theory to Machine Learning

Supercritical Methane Adsorption Characteristics and Pore Structure Characteristics of Deep Middle Rank Coal

Abstract In order to accurately analyze the adsorption characteristics, pore structure, and fractal law of deep middle rank coal, high-pressure isothermal adsorption tests based on magnetic levitation high-pressure thermobalance and pore structure tests based on mercury intrusion method were carried out on coal samples collected from typical kilometer level deep wells. The fractal law of sponge model was studied. The results showed that: a. The weight method adsorption test showed “excess adsorption” phenomenon with the increase of equilibrium pressure, and the modified Gibbs surface excess adsorption theory was in line with the Langmuir adsorption model; b. The distribution of macropore volume in deep middle rank coal accounts for a dominant proportion of 57.44% to 62.47%, and the proportion of microporous specific surface area reaches 72.96% to 74.27%, indicating that microporous adsorption capacity is the strongest; c. The pore structure parameters and adsorption constants exhibit strong nonlinear characteristics.

High-Pressure adsorption of supercritical methane and carbon dioxide on Coal: Analysis of adsorbed phase density

The occurrence of supercritical CH4 and CO2 in coal is significant for both coalbed methane recovery and CO2 storage. Adsorption isotherms of CH4 and CO2 on two coals have been measured at three temperatures up to pressures of 25 MPa. Three modified supercritical adsorption models (SL-V, SBET-V, and SDR-V) were used to describe the excess adsorption behavior, with the pressure-independent adsorbed phase volume being considered. The adsorbed phase density (APD) and absolute adsorption amount were calculated based on the modified models and compared with those estimated by previous models. The results indicate that SDR-V is the most suitable for CH4 adsorption due to the dominant role of filling of micropores by CH4, while SBET-V is the most appropriate model for CO2 adsorption because of multilayer adsorption of CO2 in both micropores and meso-macropores. The APD increases with pressure until reaching a maximum value but decreases as temperature increases following a Langmuir-style trend. The previous models, which use a fixed APD, seriously underestimate the absolute adsorption, the extent of which increases with increasing pressure and temperature, leading to significant errors in deep formations with high temperature and pressure conditions. Furthermore, as burial depth increases, the adsorption process can be divided into three stages based on changes in APD and free phase density (FPD). These findings contribute to a comprehensive understanding of the behavior and occurrence of CH4 and CO2 within deep coal seams, enhancing the applicability of CO2-ECBM (CO2 Geological Storage Enhanced Coalbed Methane Recovery).

Supercritical methane adsorption in coal and implications for the occurrence of deep coalbed methane based on dual adsorption modes

Supercritical methane adsorption in coal and implications for the occurrence of deep coalbed methane based on dual adsorption modes

Kinetic and Thermodynamic Characteristics of Supercritical Methane Adsorption on Organic-Rich Shale: A Case Study of Ordovician Wufeng and Silurian Longmaxi Gas Shale

Kinetic and Thermodynamic Characteristics of Supercritical Methane Adsorption on Organic-Rich Shale: A Case Study of Ordovician Wufeng and Silurian Longmaxi Gas Shale

Investigations on Supercritical Methane Adsorption and Storage in the Lower Longmaxi Shale of Nanchuan Area, Southeast Sichuan Basin

A series of high-pressure methane adsorption measurements were performed at various temperatures on whole shale and kerogen samples collected from the Lower Longmaxi shale in the Nanchuan area, southeast Sichuan Basin, to investigate supercritical methane adsorption properties and evaluate in-place methane storage capacity as a function of burial depth. The results show that the supercritical Dubinin–Radushkevich (SDR) model fits the excess adsorption isotherms marginally better than the supercritical Langmuir model. However, the fitted adsorbed methane density of kerogens obtained from the SDR model may be greater than the liquid methane density at the atmospheric boiling point (0.423 g/cm3). The proposed multiple regression fitting carried out in this work illustrates that approximately 57.59% (34.51–85.45%) and 37.60% (10.74–59.52%) of the methane adsorption capacity at 333.15 K can be attributed to organic matter (OM) and clay minerals (CMs), respectively, for whole shales investigated. According to thermodynamic analyses, the significant contribution of OM to the methane adsorption capacity can be attributed to the stronger affinity between kerogens and methane molecules in contrast to that between CMs and whole shales. The methane storage capacity estimated as a function of burial depth showed that the adsorbed gas storage capacity declines with increasing burial depth between 2000 and 5000 m, while the free gas storage capacity shows the opposite trends. Gas accumulation pressure primarily exerts a significant effect on the free gas storage capacity rather than adsorbed gas storage capacity, and adsorbed gas storage capacity begins to exceed free gas storage capacity at shallow burial depths for normally pressured gas accumulations. Normally pressured shale gas accumulations at shallow burial depths, which are widely distributed in the residual syncline of the study area, should be given more attention due to their relatively low development costs and relatively high storage capacity for adsorbed gas.

Perspectives of Gas Adsorption and Storage in Kerogens and Shales

Shale gas from unconventional resources will contribute to meeting the energy demand during the transition to a net-zero carbon economy. In this minireview, the current status of understanding methane adsorption on kerogens and shales is discussed in relation to methane storage capacity. Standard subcritical adsorption studies provide characterization data (micropore volumes, total pore volumes, surface areas, and pore size distributions) for the porous structures of shales and kerogens. However, supercritical methane adsorption measurements under simulated geological conditions are necessary to assess realistic methane adsorption storage capacities. Supercritical methane adsorption on shale and shale components (kerogens and clays) under high pressure and temperature conditions that simulated geological conditions is compared. Kerogen structural characteristics are discussed in relation to supercritical methane isotherms and isobars. The contribution of adsorbed methane gas relative to “free” or compressed gas to the total gas stored in shale is considered. The importance of kerogens in both storage of the adsorbed phase and as the source of methane is highlighted, and the areas where knowledge and understanding are deficient are identified, in particular, the relationship of kerogen type and maturity with supercritical methane adsorption under simulated geological conditions. The competitive adsorption of water on methane capacity is also an area where more detailed studies are necessary. These are challenges to address gaps in the current knowledge and understanding, which require future research.

Examining Supercritical Methane Adsorption on Nanoporous Shales Using Constant and Varying Adsorbed Phase Density Approaches

Supercritical adsorption studies are crucial, as adsorbed methane has a significant contribution to the total gas-in-place along with the free gas-in-shale reservoirs. Due to the low specific adsorption of shales, Gibbs excess isotherms that decrease after a certain pressure are being reported. Corrections to the excess adsorption amount can be made using models that predict absolute adsorption through empirically estimated adsorbed phase density. However, due to the inherent heterogeneity of shale and uncertainties in the adsorbed phase density estimated from different models, the quantitative characterization of adsorption is becoming increasingly challenging. The assumption of constant adsorbed phase density is being challenged with varying adsorbed phase density approaches, which are theoretically correct; however, their applicability has not been analyzed distinctively. In this work, supercritical adsorption models like supercritical BET (SBET), supercritical Dubinin–Radushkevich (SDR), Ono–Kondo mono- and multilayer, fixed volume Ono–Kondo (FV-OK1), and variable density Langmuir (VD-Langmuir) are revisited, analyzed, and compared for their applicability in shale reservoirs. For this, methane adsorption isotherms at two different temperatures (45 and 90 °C) are generated for four samples with varying geochemical and petrophysical properties selected from the Cambay and Krishna–Godavari (KG) basins of India. Through this analysis, it has been found that fixed-density approaches better explain the isotherms in comparison to varying density approaches. The average adsorbed phase density estimated using SBET and SDR models was closer to 0.2 g/cm3, which is very low in comparison to the theoretical limit. The SBET and Ono–Kondo theories have displayed that the probability of adsorption after the third layer is low. The VD-Langmuir and FV-OK1 could fit perfectly to highly specific adsorbing solids; however, they failed to explain adsorption in low-adsorbing solids. The mathematical drawbacks of variable density approaches have not been analyzed previously and are explained in this work.

Absolute adsorption and adsorbed volume modeling for supercritical methane adsorption on shale

Adsorbed methane significantly affects shale gas reservoir estimates and shale gas transport in shale formations. Hence, a practical model for accurately representing methane adsorption behavior at high-pressure and high-temperature in shale is imperative. In this study, a reliable mathematical framework that estimates the absolute adsorption directly from low-pressure excess adsorption data is applied to describe the excess methane adsorption data in literature. This method provides detailed information on the volume and density of adsorbed methane. The obtained results indicate that the extensively used supercritical Dubinin-Radushkevich model with constant adsorbed phase density underestimates absolute adsorption at high pressure. The adsorbed methane volume increases both the pressure and expands with the temperature. The adsorbed methane density reduces above 10 MPa, and approaches a steady value at high pressure. This study provides a novel method for estimating adsorbed shale gas, which is expected improve the prediction of shale gas in place and gas production.

Characteristics and Influencing Factors of Supercritical Methane Adsorption in Deep Gas Shale: A Case Study of Marine Wufeng and Longmaxi Formations from the Dongxi Area, Southeastern Sichuan Basin (China)

Characteristics and Influencing Factors of Supercritical Methane Adsorption in Deep Gas Shale: A Case Study of Marine Wufeng and Longmaxi Formations from the Dongxi Area, Southeastern Sichuan Basin (China)

Supercritical methane adsorption measurement on shale using the isotherm modelling aspect.

In shale gas reservoirs, adsorbed gas accounts for 85% of the total shale gas in place (GIP). The adsorption isotherms of shale samples are significant for understanding the mechanisms of shale gas storage, primarily for assessing the GIP and developing an accurate gas flow behaviour. Isothermal adsorption experiments primarily determine the adsorption capacity of methane in shale gas reservoirs. However, experimental data is limited due to the heterogeneous properties of shale and extreme reservoir conditions at high pressures and temperatures. This work discusses the effect of total carbon (TOC), pore size distributions, and mineralogical properties on adsorption capacity. In this study, the gravimetric adsorption isotherm measurement method was applied to obtain the adsorption isotherms of methane on four shale core samples from Eagle Ford reservoirs. Four shale core samples with TOC of 9.67% to 14.4% were used. Adsorption experiments were conducted at a temperature of 120 °C and to a maximum pressure of 10 MPa. The data obtained experimentally were compared with adsorption isotherm models to assess each model's applicability in describing the shale adsorption behaviour. A comparison of these models was performed using fitting and error analysis. It was observed that the calculated absolute adsorption of supercritical methane is higher than the excess adsorption. The percentage of differences between the absolute and excess adsorption is more significant at a pressure higher than the critical methane pressure of 9.6%. Sample EF C has the highest adsorption capacity of 1.308 mg g−1, followed by EF D 1.194 mg g−1, EF B 0.546 mg g−1, and EF A 0.455 mg g−1. Three statistical error analyses, average relative error (ARE), the Pearson chi-square (χ2) test and root mean square error (RMSE) deviation were used to assess the applicability of each model in describing the adsorption behaviour of shale samples. The order of adsorption isotherm fitting with experimental data is Toth > D–R = Freundlich > Langmuir. Error analysis shows that the Toth model has the lowest values compared to other models, 0.6% for EF B, 2.5% for EF C, and 2.2% for EF A and EF D, respectively.

Supercritical High-Pressure Methane Adsorption on the Lower Cambrian Shuijingtuo Shale in the Huangling Anticline Area, South China: Adsorption Behavior, Storage Characteristics, and Geological Implications

Supercritical high-pressure methane (CH4) adsorption analysis was performed to investigate the gas adsorption behavior and storage capacities of the Lower Cambrian Shuijingtuo Shale in the Huanglin...

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

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 ...

Adsorption and absorption of supercritical methane within shale kerogen slit

Gas storage in shale primarily includes three forms: free gas in the fractures or macropores, adsorbed gas upon the kerogen surface, and absorbed gas in the kerogen matrix. However, current techniques cannot distinguish the adsorbed and absorbed gas, which restrict the understanding of gas storage and transport mechanisms through shale kerogen. On the basis of the grand canonical Monte Carlo (GCMC) simulations, we propose a technique to determine the independent adsorption and absorption isotherms of methane within slit-shaped shale kerogen under supercritical conditions. We observe that if the pore pressure is higher than ~3.5 MPa, the absorption amount is much smaller than that of adsorbed gas; however, at lower pressures, the absorption capacity is superior to that of the adsorption. Meanwhile, the ratio between adsorption and absorption quantities continuously increases with pressure. We probe the underlying mechanisms and study the effect of slit aperture, temperature, as well as moisture on gas adsorption and absorption capacity. Enlarging the slit aperture increases the adsorbed gas contents but shows only a negligible effect on the absorption capacity. Heating facilitates the escapement of gas molecules, thus leading to the inhibition of both adsorption and absorption capacities. Water molecules occupying the adsorption site on the slit surface impedes methane adsorption, but the absorption capacity within the kerogen matrix remains unchanged. This work elucidates the gas adsorption and absorption behavior in shale kerogen and sheds light on the storage and transport of hydrocarbons in nanoporous materials.

Supercritical methane adsorption and storage in pores in shales and isolated kerogens

Shale gas is an important hydrocarbon resource in a global context. It has had a significant impact on energy resources in the US, but the worldwide development of this methane resource requires further research to increase the understanding of the relationship of shale structural characteristics to methane storage capacity. In this study a range of gas adsorption, microscopic, mercury injection capillary pressure porosimetry and pycnometry techniques were used to characterize the full range of porosity in a series of shales of different thermal maturity. Supercritical methane adsorption methods for shale under conditions which simulate geological conditions (up to 473 K and 15 MPa) were developed. These methods were used to measure the methane adsorption isotherms of Posidonia shales where the kerogen maturity ranged from immature, through oil window, to gas window. Subcritical methane and carbon dioxide adsorption studies were used for determining pore structure characteristics of the shales. Mercury injection capillary pressure porosimetry was used to characterize the meso and macro porosity of shales. The sum of the CO2 sorption pore volume at 195 K and mercury injection capillary pressure pore volumes (1093–5.6 nm) were equal to the corresponding total pore volume (< 1093 nm) thereby giving an equation accounting for virtually all the available shale porosity. These measurements allowed quantification of all the available porosity in shales and were used for estimating the contributions of methane stored as ‘free’ compressed gas and as adsorbed gas to overall methane storage capacity of shales. Both the mineral and kerogen components of shale were studied by comparing shale and the corresponding isolated kerogens so that the relative contributions of these components could be assessed. The results show that the methane adsorption characteristics were much higher for the kerogens and represented 35–60% of the total adsorption capacity for the shales used in this study, which had total organic contents in range 5.8–10.9 wt%. Microscopy studies revealed that the pore systems in clay-rich, organic-rich and microfossil-rich parts of shale are very different, and also the importance of the inter-granular organic-mineral interface.

Modeling High-Pressure Methane Adsorption on Shales with a Simplified Local Density Model.

Shale gas has attracted increasing attention as a potential alternative gas in recent years. Because a large fraction of gas in shale formation is in an adsorbed state, knowledge of the supercritical methane adsorption behavior on shales is fundamental for gas-in-place predictions and optimum gas recovery. A practical model with rigorous physical significance is necessary to describe the methane adsorption behavior at high pressures and high temperatures on shales. In this study, methane adsorption experiments were carried out on three Lower Silurian Longmaxi shale samples from the Sichuan Basin, South China, at pressures of up to 30 MPa and temperatures of 40, 60, 80, and 100 °C. The simplified local density/Elliott–Suresh–Donohue model was adopted to fit the experimental data in this study and the published methane adsorption data. The results demonstrate that this model is suitable to represent the adsorption data from the experiments and literature for a wide range of temperatures and pressures, and the average absolute deviation is within 10%. The methane adsorption capacity of the Longmaxi shale exhibited a strong linear positive correlation with the total organic carbon content and a linear negative correlation with increasing temperature. The rate of decrease in the methane adsorption capacity with swing temperature increased with the total organic carbon content, indicating that the organic matter is sensitive to temperature.

Supercritical Methane Adsorption on Shale over Wide Pressure and Temperature Ranges: Implications for Gas-in-Place Estimation

Methane adsorption experiments over wide ranges of pressure (up to 30 MPa) and temperature (30-120 °C) were performed using a gravimetric method on the Longmaxi shale collected from the northeast boundary of Sichuan Basin, China. Organic geochemical analyses, shale composition determination, and porosity tests were also conducted. The experimental supercritical methane excess adsorption isotherms at different temperatures initially increase and then decrease with increasing pressure, giving a maximum excess adsorption capacity (Gexm = 1.86-2.87 cm/g) at a certain pressure P (6.71-12.90 MPa). The excess adsorption capacity decreases with increasing temperature below 28 MPa, while this effect reversed above 28 MPa. However, the absolute adsorption capacity decreases as the temperature increases over the full pressure range. Supercritical methane adsorption on shale is of temperature dependence because it is a physical exothermic process supported by calculated thermodynamic parameters. P is positively correlated with the temperature, while the decline rates (0.021-0.058 cm g MPa) in excess adsorption negatively correlate with the temperature. Meanwhile, Langmuir volume G (3.07-4.04 cm/g) decreases while Langmuir pressure P (1.44-4.31 MPa) increases with temperature elevation. In comparison to the actual adsorbed gas (absolute adsorption), an underestimation exists in the excess adsorption calculation, which increases with increasing depth. The conventional method, without subtracting the volume occupied by adsorbed gas, overestimates the actual free gas content, especially for the deep shale reservoirs. In situ adsorbed gas is simultaneously controlled by the positive effect of the reservoir pressure and the adverse effect of the reservoir temperature. Nevertheless, in situ free gas is dominated by the positive effect of the reservoir pressure. Lowerature overpressure reservoirs are favorable for shale gas enrichment. Geological application of gas-in-place estimation shows that, with increasing depth, the adsorbed gas content increases rapidly and then declines slowly, whereas the free gas content increases continuously. There was an equivalence point at which the contents of adsorbed and free gas are equal, and the equivalence point moved to the deep areas with increasing water saturation. Moreover, the adsorbed gas and free gas distribution are characterized by the dominant depth zones, providing the reference for shale gas exploration and development.

Isotherms, thermodynamics and kinetics of methane-shale adsorption pair under supercritical condition: Implications for understanding the nature of shale gas adsorption process

This research article selects supercritical methane and organic-rich shale as adsorbate-adsorbent pair to investigate methane adsorption behavior and enrich our understanding of the nature of shale gas adsorption process. The isotherms and kinetics of methane-shale adsorption pair are measured at temperatures of 303 K, 323 K, 343 K and 363 K by using a volumetric experimental setup. Then, the Langmuir-based (Langmuir, Langmuir + k, Langmuir + Henry), BET-based (BET, BET + k, BET + Henry) and DA-based (DA, DA + k and DA + Henry) excess models are used to interpret measured excess isotherms, and the Unipore Diffusion (UD), Bidisperse Diffusion (BD) and Two Combined First-Order Rate (TCFOR) models are used to interpret the adsorption kinetics data. Instead of using the coefficient of determination (R2), this work used the corrected Akaike’s Information Criterion (AICc) for model selection. It is found that the DA + Henry model is more suitable for excess adsorption isotherms, and the TCFOR model is more appropriate for adsorption kinetics study. Additionally, for methane-shale adsorption under supercritical condition, the fugacity is of great significance in evaluating thermodynamic properties including isosteric heat of adsorption (qst), enthalpy change (ΔH), entropy change (ΔS) and Gibbs free energy change (ΔG). These properties show strong dependence on adsorption amount and temperature, and suggest that supercritical methane adsorption on organic-rich shale is a process of physisorption, exothermic and spontaneous. Further, the kinetics parameters extracted from kinetics curves suggest that the methane adsorption at each pressure step is a two-stage process, with a fast macropore diffusion process at early time, followed by a slow micropore diffusion process at later time. Additionally, the fast macropore diffusion dominates the two-stage adsorption process at lower pressures, while at higher pressures slow micropore diffusion dominates.

Supercritical Methane Adsorption on Overmature Shale: Effect of Pore Structure and Fractal Characteristics

To investigate supercritical methane adsorption on shale and its controlling factors, high-pressure (up to 20 MPa) methane adsorption experiments were performed on overmature Niutitang shales from ...

Study of subcritical and supercritical gas adsorption behavior in different nanopore systems in shale using lattice Boltzmann method

Adsorption has been studied for decades in either petroleum or chemical industry. However, the detailed adsorption behavior is yet not well understood in nanoporous media with complex pore structures and surface properties, especially for subcritical gases when capillary condensation might occur. Shale (mudrock) has complex pore systems as a result of heterogeneous mineralogy and diagenesis, and interparticle (interP) and intraparticle (intraP) pores are two main components. Understanding gas adsorption and phase transition behavior in different pore systems is essential for petrophysical characterization, reserve estimation and production forecast. In this study, we use lattice Boltzmann method (LBM) to study nitrogen (subcritical) and methane (supercritical) adsorption behavior in reconstructed shale nanopore systems. The model accounts for the van der Walls (vdW) forces between fluid molecules by incorporating a modified pseudopotential model based on Peng-Robinson equation of state (PR-EOS). Rock-fluid interaction is also considered by introducing phenomenological surface forces, which take two different forms for subcritical and supercritical gases respectively. The correlation between parameters defined in LBM and physical properties (i.e. density, pressure, isosteric heat of adsorption) is established systematically. Using the developed model, we observe quantitative agreement between LBM and lattice density functional theory (LDFT)/experimental data in terms of adsorption isotherms and density distributions. We then compare adsorption behavior in two ‘model’ interP and intraP pore systems and a synthesized polyethylene porous medium with more complex pore shapes. We observe three adsorption stages for subcritical gas adsorption: a) early capillary condensation near grain contacts or sharp corners, forming isolated pendular rings or fluid clusters; b) growing, merging, and spreading of the isolated condensed phase, forming circular gas/liquid meniscus; c) the condensed phase becomes fully-connected across the geometry, leaving isolated gas bubbles. We observe a signature behavior for the adsorption isotherm of intraP pore system, where a stepped feature occurs around relative pressure of 0.8, and the adsorption uptake for the polyethylene porous medium is bounded by the upper and lower limits given by the interP and intraP pore systems. On the other hand, we find that supercritical methane adsorption in mesoporous media is less sensitive to pore shape, but rather controlled by the specific surface area. The existence of micropores also affects the adsorption uptake.