Methane Density Research Articles

Effect of adsorbed phase density on the correction of methane excess adsorption to absolute adsorption in shale

In order to evaluate the accuracy of different methods for the methane excess adsorption correction, the Polanyi adsorption potential theory was introduced to analyze the absolute methane adsorption amount obtained by correction. One shale sample from the Lower Silurian Longmaxi Formation in the southern Sichuan Basin, China was selected to conduct high-pressure methane adsorption experiments at 40.6 °C, 60.6 °C, 75.6 °C, and 95.6 °C at pressures up to 52 MPa. Based on the experimental results at different temperatures, four densities (the liquid density of methane at boiling temperature and ambient pressure, the van der Waals density, the adsorbed phase density based on the falling segment fitting of excess adsorption isotherm, and the adsorbed phase density obtained by fitting excess adsorption isotherm using modified Langmuir equation) were used for the correction of excess adsorption to absolute adsorption. At the same time, in order to enhance the reliability and accuracy of the conclusions in this study, the results of methane adsorption experiments on shale in the reference were used for a comparative study to further support our conclusions. The results indicate that the greater the constant adsorbed phase density used for the excess adsorption correction, the lower the degree of overlap of the adsorption characteristic curves at different temperatures. The adsorbed phase density used for methane excess adsorption correction may be in the vicinity of 0.30 g/cm3 to 0.40 g/cm3. Particularly, it should not be greater than the liquid density of methane at boiling temperature and ambient pressure, which is 0.421 g/cm3. Although the adsorbed phase density differs across different temperatures and pressures, the current results show that 0.373 g/cm3 can be used as the adsorbed phase density for the excess adsorption correction, which may be a convenient method and can yield results close to the actual adsorption.

Methane transport in a soil column: experimental and modeling investigation

This study explored two diffusion approaches, Fick’s law and the dusty gas model (DGM), to assess their differences on modeling methane transport in porous systems. Laboratory experiments were also conducted for methane transport through a nitrogen gas-dry soil column from different source densities. Gas pressures and methane densities at transient state were measured along the column for two transport configurations (horizontal and vertically upward) and compared with the predictions obtained from the DGM- and Fickian-based models. The retardation factor is the only parameter used in the model calibration. The results showed that the methane density profiles predicted by these models fairly matched the measured data and are quite consistent for vertically upward transport of methane. However, the predictions were over the measured ones for horizontal transport of methane. We suspected it is due to incomplete mixing of gas mixture in the inlet chamber since high pressure variations were observed in the horizontal transport experiments. Further, we found that the methane density profile predicted by the Fickian-based model is lagged behind the DGM result for at most 15% of difference in methane density for horizontal transport of methane from a pure methane source.horizontal transport experiments. Further, we found that the methane density profile predicted by the Fickian-based model lagged behind the DGM result for at most 15% of difference in methane density for horizontal transport of methane from a pure methane source.

Investigation of the relationship between nanochannel width and mass transfer characteristics for dense methane nanofluidics

In this paper, we analytically investigate the influence of the nanochannel width on mass transfer characteristics through the rough nanochannel by using non–equilibrium multiscale molecular dynamics simulation. The mass transfer characteristics are analyzed by fitting the curve correlation between the diffusion coefficient and nanochannel width. The diffusion coefficient is calculated using the revised Green–Kubo relation in different nanochannels. The numerical results demonstrate that the relationship between diffusion coefficient and the inverse of nanochannel width is parabolic. Moreover, the diffusion coefficients show significant variations in the small rough nanochannel, and gradually approach the values of bulk system with increasing the width of nanochannel. In addition, to explore its mechanism, the local atom number density, velocity profile, velocity autocorrelation function, the escape rate of molecule, local diffusion coefficient and projection radial distribution function are given in different widths of nanochannel under given boundary condition. Simulation results show that the local structure and number density of fluid influence the transfer mass characteristics. These results of this work may be conducive to further understand the mass transfer behaviors of nanofluidics, and guide the optimal design of nano–devices.

An analytical model for coalbed methane transport through nanopores coupling multiple flow regimes

Understanding the complex transport behavior of methane in coal matrix pores is very important for coalbed methane exploitation. One important approach is to model the transport process of methane in coal matrix nanopores. In this work, we modelled the coalbed methane transport process in coal matrix nanopores, coupling gas adsorption, real (i.e. non-ideal) gas and gas slippage effects, and a new method is proposed to characterize the governing equation of transport flow regime. It was found that the proposed model agreed well with the published data on methane physical properties (viscosity and density) and coal permeability. We also focused on the influence of temperature and pore pressure on the flow regime, Knudsen number, surface diffusion and bulk gas flow in the model. The results indicate that under typical reservoir conditions, the real gas and gas adsorption effects have a significant impact on methane viscosity, density and apparent permeability. It was also found that the mass flow rate of methane by surface diffusion increases when pore pressure increases up to about 5 MPa, but tends to decrease when pore pressure increases above about 5 MPa. For any given pore, the flow mechanism of the bulk gas can change from one mechanism to another as the temperature and pore pressure conditions change. The governing equation of the transition flow regime can be regarded as a weighted superimposition of the slip flow equation and Knudsen diffusion equation. However, under reservoir conditions, the Knudsen diffusion regime and the transition flow regime are negligible. This work will provide a theoretical basis to assist with the effective development of coalbed methane.

NUMERICAL MODEL ON METHANE EMISSIONS FROM AGRICULTURE SECTOR

Atmospheric methane, emitted from agriculture sector such as production of rice paddies and farming of livestock populations, is one of the important factors responsible for increasing the average atmospheric temperature leading to global warming. It is, therefore, crucial to comprehend the dynamics of methane emission and its effect on global warming. In this paper, a nonlinear mathematical model is proposed and analyzed to study the increase of average atmospheric temperature (or average global warming temperature) caused by emission of methane due to various processes involved in the production of rice paddies and farming of livestock populations simultaneously. In the modeling process, six variables are considered, namely, the cumulative biomass density of rice paddies, the cumulative density of livestock populations, the cumulative density of methane formed by various processes involved in the production of rice paddies, the cumulative density of methane formed by various processes involved in the farming of livestock populations, the atmospheric concentration of methane and the average atmospheric temperature. It is assumed that both the cumulative biomass densities of rice paddies and livestock populations follow logistic models with their respective growth rates and carrying capacities. The growth rate of concentration of methane in the atmosphere is assumed to be directly proportional to the cumulative densities of various processes involved in the production of rice paddies as well as in the farming of livestock populations. This growth rate also increases with a constant rate from various natural sources such as wetlands, etc. The growth rate of average global warming temperature is assumed to be proportional to the increased level of methane concentration in the atmosphere from its equilibrium value. It is also assumed that this temperature decreases with a rate proportional to its enhanced level from its equilibrium level caused by various natural factors such as rain fall, snowfall, etc. The proposed model is analyzed using the stability theory of differential equations and numerical simulation. The analysis shows that as the emission of methane from various processes involved in the production of rice paddies and farming of livestock populations increase, the average global warming temperature increases considerably from its equilibrium level. The numerical simulation of the model confirms the analytical results.

Extended calibration of a vibrating tube densimeter and new reference density data for a methane-propane mixture at temperatures from (203 to 423) K and pressures to 35 MPa

In this work, the lowest operational temperature of a commercial vibrating tube densimeter (VTD) calibrated using a robust physically-based model was carefully extended down to 203 K. The VTD was calibrated under vacuum and filled with pure gaseous methane and liquid propane as calibration reference fluids at temperatures from (203 to 423) K and pressures up to 35 MPa. The calibration parameters were obtained by linear and nonlinear regression of the calibration data (period of oscillation, temperature and pressure) to the physically-based calibration model. The relative deviations between the fitted densities of methane or propane and those predicted by the corresponding default reference equations of state were between (−0.56 to 0.60) % and the relative root mean square error was 0.30%. This wide-ranging calibration model was then employed for single-phase density measurements of a 0.95 methane + 0.05 propane mixture at a temperature of 203 K and pressures up to 35 MPa. Additionally, two sets of measurements at pressures approaching the bubble point at (203 and 208) K were completed. The measured densities ranged from (243 to 369) kg·m−3, with combined standard relative uncertainties between (0.31 and 0.42) %. The relative deviations of the measured densities from those calculated using the GERG-2008 equation of state spanned between (−0.5 to 0.4) %. This work demonstrates the potential of using the physically-based calibration model for VTDs at significantly low temperatures than previously attempted.

Flame Stability in Inverse Coaxial Injector Using Repetitive Nanosecond Pulsed Plasma

Abstract Recently, methane has been investigated as a feasible fuel for propulsion systems. The higher boiling point and higher density of methane, compared with hydrogen, makes its storage tank lighter, cheaper, and smaller to launch. Methane is abundant in the outer solar system and can be harvested on Mars, Titan, Jupiter, and many other planets and therefore, it can be used in reusable rocket engines. However, there are still some technological challenges in the methane engines development path. For example, ignition reliability and flame stability are of great importance. These challenges can be addressed by integrating low-temperature plasma (LTP) through repetitive nanosecond pulsed (RNP) discharge to the injector design. This research focuses on air/CH4 jet flames in a single-element coaxial shear injector coupled with RNP plasma discharge to study the influence of LTP on ignition characteristics and flame stability using advanced diagnostic techniques. The experiments have been performed for different fuel composition, jet velocities, discharge voltages, and frequencies at atmospheric conditions. The transient flame behavior including flame oscillation is studied using direct photography by CMOS high-speed camera. The effect of plasma discharge location on flame stability is also investigated. To demonstrate the effectiveness of RNP discharge on liftoff and blowout/blowoff velocities, the jet velocity at the critical conditions is measured and the enhancements of flame stability are then evaluated. The collected experimental data have shown that the RNP discharge can significantly extend the stability by reducing the liftoff height and increasing the velocity of blowout/blowoff phenomena.

Molecular dynamics of methane flow behavior through realistic organic nanopores under geologic shale condition: Pore size and kerogen types

Up to date, for the purpose of simplicity, graphene-based structures, like nano-porous carbons or carbon nanotubes, have been widely utilized to investigate methane flow behavior inside shale organic nanopores. However, realistic shale organic matrix is composed of kerogen molecules, possessing complex amorphous structures and apparently different surface attributes compared with graphene-based nanopore surface, which will inevitably have a great impact on surface-methane interactions and methane flow behavior. Current research works in terms of the graphene-based material fails to capture the influence of kerogen surface, and therefore cannot accurately characterize nano-confined methane flow behavior through realistic shale organic matter. Also, shale organic nanopores with different kerogen types contain different surface compositions, while its impact on methane flow capacity has not been reported yet. To bridge this knowledge gap, this paper simulates the methane flow behavior through authentic kerogen-based circular nanopores with the use of molecular dynamics (MD) for the first time. And a novel construction method was developed to generate kerogen-based organic nanopores with desirable pore size and different kerogen types for MD simulation. Main results show that a) decrease in pore size will contribute to the enhancement of adsorption capacity for nanopores and type-III kerogen > type-II kerogen > type-I kerogen in terms of methane adsorption capacity; b) ratio of average methane density confined in nanopores to bulk-gas density ranges from 1.2 to 2.6, which will decrease with the increase of the pressure and increase with decreasing pore size; c) Under shale geological condition, the conventional theoretical model for nanoconfined gas flow will underestimate that of 0.41 time for type-I kerogen-based nanopores, 0.59 time for type-II kerogen-based nanopores, and 0.88 time for type-III kerogen-based nanopores.

Insights into recovery of multi-component shale gas by CO2 injection: A molecular perspective

Understanding the mechanism behind shale gas recovery is of great importance for achieving optimum shale gas productivity. In this work, we use Grand Canonical Monte Carlo (GCMC) simulations to investigate the adsorption and recovery mechanisms of ternary hydrocarbon mixtures comprising methane, ethane and propane in kerogen nanopores. For the adsorption of hydrocarbon mixtures in kerogen slit pores, density distributions of each component are analyzed and the results indicate that densities of methane and ethane in the first adsorption layer increase as pressure increases, while an opposite trend is observed for propane. A stronger confinement effect is observed on the heavier hydrocarbon components, increasing the difficulty of recovery. For the recovery of the multi-component shale gas, we propose a reference recovery route with pressure drawdown and CO2 injection combined and the recovery efficiency is compared to the condition with only pressure drawdown applied. Significant enhancement in recovery ratio for all three components is observed with the CO2 injection and a better performance is shown on heavier components and smaller pores. An increase of 60% and 40% in propane recovery ratio is achieved in the 2-nm and 4-nm kerogen slit pores, respectively. Recovery mechanisms of pressure drawdown and CO2 injection are investigated in detail. The pressure drawdown method recovers methane from the first adsorption layer and middle of slit pore simultaneously, while extracting ethane and propane mainly from the middle of slit pore; the recovery due to CO2 injection mainly takes place in the adsorption layers. Pressure drawdown tends to extract the lighter components and CO2 injection is efficient in the recovery of heavier hydrocarbons. As pore width increases, the recovery ratio of pressure drawdown increases, while that of CO2 injection decreases. Besides, the CO2 sequestration ratio is higher in smaller kerogen slit pores.

A Tangent-Line Approach for Effective Density Used in Ideal Mixing Rule: Part I—Prediction of Density for Heavy-Oil/Bitumen Associated Systems

SummaryAccurate prediction of density of an oil/gas mixture by using the ideal mixing (IM) rule is a great challenge, and its progress is still far from satisfactory. The method proposed by Standing and Katz (1942) for determining methane and ethane apparent densities is limited to only black oils and volatile oils. The methods recently proposed by Saryazdi (2012) and Saryazdi et al. (2013) to determine effective densities of methane through n-heptane (C1 through n-C7) and CO2 have shown some success, respectively, though limitations remain and the extent of their applications is still constrained. In this study, we developed a tangent-line approach for the effective density of C1 through n-C8, CO2, N2, toluene, cyclohexane, and dimethyl ether (DME). This method is more general and flexible than the extrapolation method proposed by Saryazdi (2012). A comprehensive database is established to first develop new correlations with one set of data and then compare them with the other. We successfully extended using the IM rule with effective density (IM-E) to condensate/bitumen systems, solvent/bitumen fraction systems, and solvent/bitumen systems with substantial extraction [i.e., emergence of a solvent-rich liquid phase (denoted as the L1 phase)] by properly treating the densities of condensate, bitumen fractions, extracts, and residues. This study focuses on heavy-oil/bitumen-associated systems, and the observed patterns and trends for different systems will be presented and explained in Part II of this study (Chen and Yang 2020).

Theoretical Analysis of the Composition and Thermodynamic Parameters of Products Formed in Combustion of 2,2'-Bis(bicyclo[2.2.1]heptane) in Oxygen

Theoretical analysis was made on the composition and thermodynamic parameters of combustion products of 2,2'-bis(bicyclo[2.2.1]heptane) in oxygen in a wide range of temperatures and pressures. 2,2'-Bis(bicyclo[2.2.1]heptane) can potentially be used as a fuel component in combustion chambers of liquid rocket engines for the first-stage launch vehicles. The average molar mass of approximately 26 amu., obtained for products formed in combustion of 2,2'-bis(bicyclo[2.2.1]heptane) in oxygen is close to similar values for methane in oxygen, whereas its density is more than twice the density of liquid methane. This circumstance makes it possible to hope that the mass of storage tanks can be made smaller if 2,2'-bis(bicyclo[2.2.1]heptane) is used for rockets, compared with the mass of storage tanks containing an equivalent amount of methane. The results obtained can be used to calculate nozzle profiles and combustion chamber parameters of a liquid jet propulsion engines.

Molecular scale modeling approach to evaluate stability and dissociation of methane and carbon dioxide hydrates

A comprehensive knowledge and precise estimation of the dynamic, structural, and thermodynamic characteristics of hydrates are needed to assess the stability of gas hydrates. Thermodynamic model and experimental studies can be utilized to compute the physical and dynamic properties of hydrate structures. The use of molecular dynamic (MD) simulation is a well-established approach in gas hydrate studies at the atomic level where the properties of interest are obtained from the numerical solution of Newtonian equations. The present work uses MD simulations by employing the constant temperature-constant pressure (NPT), constant temperature-constant volume (NVT) conditions, and the consistent valence force field (CVFF) to monitor the stability and decomposition of methane and carbon dioxide gas hydrates with different compositions. The effects of temperature and composition on the hydrate stability are investigated. In this study, we also compute the radial distribution function, mean square displacement, diffusion coefficient, lattice parameter, potential energy, dissociation enthalpy as well as the density of methane and carbon dioxide under various thermodynamic and process conditions. The formation of methane and carbon dioxide bubbles is studied to investigate bubble evolution during hydrate dissociation. The sizes of methane and carbon dioxide bubbles are not the same due to different solubility conditions of methane and carbon dioxide in liquid water. In addition, the influences of pressure and temperature on the lattice parameter and density of clathrate hydrates are discussed. The obtained results are consistent with previous theoretical and experimental findings, implying that the methodology followed in this work is reliable. The most stable arrangement of methane and carbon dioxide molecules in the gas hydrate is found. The insights/findings of this study might be useful to further understand detailed transport phenomena (e.g., molecular interactions, gas production rate, carbon dioxide replacement, and carbon dioxide capture) involved in the process of carbon dioxide injection into gas hydrate reservoirs.

Spatio-temporal distribution of sewage sludge, its methane production potential, and a greenhouse gas emissions analysis

With ongoing economic development and population growth in China, large quantities of wastewater are discharged and substantial amounts of sewage sludge are generated, which is a potential biomass resource for methane production. This study used data from statistics yearbooks and literatures to evaluate the spatio-temporal distribution of sludge generation, potential and distribution of methane production from sludge, and the potential of greenhouse gas (GHG) emissions reduction (PGER) from sludge treatment and disposal in provinces in mainland China. The results showed that a total of 6.03 Mt of dry solids in 2015. The eastern part of the country produced more sludge than that the western part. The standard coal equivalence of sludge was 3.5 Mt, ranged from 0.7 to 399.8 Kt, among the 31 provinces of mainland China. Total sludge could produce 1.27 billion m 3 of methane per year through anaerobic digestion (AD). The distribution of methane density exhibited that the east part was higher than the west part in China. The GHG emissions totaled 18.82 Mt CO 2 -eq as a baseline for the current sludge disposal methods without AD technology. The PGER was 10.77 Mt CO 2 -eq for the sludge disposal routes with AD technology. The sludge disposal for the project route of building material exhibited the highest PGER of 4.24 Mt CO 2 -eq among the disposal methods. As the least GHG emissions method, sludge treated by AD and the residue disposed for land using as fertilizer should be recommended. Our findings provide a sludge disposal reference for the government and industries. For further study, it is suggested to take the co-digestion technology into consideration for sewage sludge to produce methane, which would perform a higher methane production and GHG emissions reduction potential. • A total of 6.03 Mt dry solids of sludge were generated in China in 2015. • Dry sludge with calorific value of 3.5 Mt was generated in 2015. • Methane production potential from sludge was estimated at 1.27 billion m 3 in 2015. • Land application after anaerobic digestion can reduce GHG by 177.7 Kt CO 2 -eq.

New perspectives on supercritical methane adsorption in shales and associated thermodynamics

Understanding methane adsorption behavior in shales is fundamental for optimizing shale gas development as the adsorbed methane is a large portion of the subsurface shale gas resource. However, the adsorption mechanism of supercritical methane in shales and associated thermodynamics are poorly understood because the equation of state of the adsorbed methane is unmeasurable. This work analyzed adsorption equilibria (up to 32MPa and 393.15K) using a rigorous framework that can account for non-ideal gas properties and accurately extrapolate absolute adsorption uptakes from measured adsorption isotherms. The framework also allows a straightforward calculation of thermodynamic potentials relevant to adsorption such as enthalpy and entropy. Modelling results show that methane adsorption isotherms in shale under different pressures and temperatures are represented by a two dimensional adsorption isotherm surface. The density of the adsorbed methane in shales depends on temperature and pressure, which is always lower than the liquid methane density but higher than the corresponding gaseous methane density. The temperature-dependent and pressure-dependent characteristics of adsorbed methane density leads to the corresponding temperature-dependent and pressure-dependent measured/absolute adsorption isotherms. The maximum adsorption uptake of shales is independent of temperature and pressure. The isosteric enthalpy/entropy of adsorption and enthalpy/entropy of adsorbed methane are found to be temperature- and surface coverage-dependent. These new findings therefore not only clarify some historical misunderstandings of methane adsorption in shales for engineering application, but also provide a novel framework for interpreting methane adsorption behavior in shales and for determining the associated thermodynamics.

COMPARISON OF POTENTIALALLY DANGEROUS FACTORS WITH THE USE OF RARE AND GASILY VEHICLE

A detailed analysis of the potentially dangerous factors in the use of diesel, gasoline, methane and propane-butane fuels was carried out in cars. A detailed analysis of potentially dangerous factors when using diesel, gasoline, methane and propane-butane fuels in automobiles has been carried out. 6 options of fuel usage are considered: a tank with g asoline and a system supplying it to the carburetor and further to the engine cylinders, a tank with diesel fuel and the system feeding it to the engine cylinders, gas cylinder installation when installing cylinders with methane on the roof of the car, gas cylinder installation when mounting cylinders with methane in the luggage compartment of the car, gas installation when installing cylinders with propane-butane mixture on the roof of the car, gas installation when installing cylinders with propane-butane mixture in the cargo compartment of the car. Meanwhile, the potential danger while the vehicle is in motion is analyzed, as well as while it is in the open parking lot and in the garage. As the initial data, the common operation period was taken - in summer with the temperature of 30°C and possible fuel leakage with the probability of formation of an explosive mixture. Nonane is taken as a model when considering gasoline, and Pentadecane is used for diesel fuel.
 It was noted that the gasoline self-ignition temperature ranges from 255°С to 435°0С, the lower concentration limit of petrol explosiveness can be considered as 0.76% vol., while under selected conditions indoors, gasoline vapor can reach the concentration of up to 0.8 vol. %. The relative vapor density of diesel fuel betting the same conditions is 8.52 kg/m3. With the explosion, the pressure in the closed volume will reach 5.2 atm.
 It was noted that the gasoline self-ignition temperature ranges from 210°С to 370°0С, the lower concentration limit of petrol explosiveness can be considered as in % vol., while under selected conditions indoors, gasoline vapor can reach the concentration of up to 0.13 vol. %. With the explosion, the pressure in the closed volume will reach 5.0 atm.
 The self-ignition temperature of methane is 537°C, the lower concentration limit of explosiveness of this gas is 5.28% (vol). The vapor density of methane at the temperature of 300°C (303K) is 0.64 kg/m3, which is significantly less than the density of air. The explosion pressure in the closed volume will reach 7.7 atm.
 The propane-butane mixture used in summer contains about 40% of propane and 60% of butane. Spontaneous ignition temperature of propane is 4700C, butane is 4050C. The calculated lower explosion limit of this mixture is 1.5% (vol), and the vapor density of mixture at the temperature of 300°C is 2.1 kg/m3, which is almost twice the density of air under the same conditions. The calculated explosion pressure in the closed volume will reach 8.3 atm.
 It was concluded that when using certified equipment which is professionally installed, methane, which cannot accumulate in the lower part of the room or any compartment, is much safer than propane-butane and, especially, than gasoline or diesel fuel, as vapor densities of both are more than air density.

Molecular simulation of methane adsorption within illite minerals in the Longmaxi Formation shale based on a grand canonical Monte Carlo method and the pore size distribution in southeastern Chongqing, China

In order to investigate the pore structure and the adsorption capacity of illite with respect to the methane in the Longmaxi Formation, isothermal adsorption experiments utilizing mercury intrusion, liquid nitrogen, and low-temperature carbon dioxide techniques were applied to the shale samples from southeastern Chongqing. The adsorption characteristics of illite slit pores varying in diameters were simulated using a Monte Carlo method. The results reveal that the pore volume and the specific surface area of the shale are primarily supplied by pore diameters measuring less than 2 nm. Illite is one of the primary components of the clay mineralogy within the shale that forms parallel or nearly-parallel plate pores. For pore sizes ranging from 0.5 nm to 0.9 nm (at conditions of 303.15 K and 8 MPa), the methane molecules are affected by van der Waals and electrostatic forces that leads to a large excess in the adsorption capacity of methane. Once the pore size becomes less than 0.9 nm, the methane adsorption becomes primarily affected by van der Waals forces. At the said size, the excess adsorption capacity of methane initially decreases, after which it remains constant with an increase in the pore size. The free gas content surges with the growing pore diameters. The average equivalent adsorption heat reflects that the adsorption of methane onto illite is characterized by physical adsorption. During the adsorption process, when the pore size is between 0.5 nm and 1.2 nm, the average equivalent adsorption heat decreases rapidly with an increase in the pore diameter. In pore size that exceeds 1.2 nm, the adsorption intensity between the methane molecules and the illite slit becomes stable. In this case, the average adsorption heat is measured to be 6.72 kJ/mol. Meanwhile, the monolayer of methane is adsorbed onto the pore wall and the local density of methane exhibits the characteristics evident of that of a single peak when the pore size is between 0.5 nm and 0.8 nm. The adsorption mode changes from single-layer adsorption to double-layer adsorption when the pore size is between 0.8 nm and 1.2 nm. In addition, the local density curve changes from unimodal to bimodal. In pores sized larger than 1.2 nm, the free volume of methane adsorption can be larger, wherein the local density curve is bimodal.

Study of High Pressure Isothermal Methane Adsorption on Shales

In order to research the problem that the Langmuir model cannot well described the experiment results of high pressure isotherm adsorption about shale gas, the Longmaxi formation shale samples which came from the CD-2 well in the Chengkou area, northeast of Chongqing were selected to the high pressure isothermal methane adsorption experiments under the reservoir temperature and pressure conditions, and used the liquid methane density under the atmospheric pressure boiling point as adsorption phase density to correct the excess adsorption capacity. The experiment results show that the excess adsorption capacity increase at the beginning and then decrease with the pressure rise and that’s the characteristic of supercritical methane adsorption. Under the high pressure isothermal conditions, the excess adsorption capacity is different from the absolute adsorption capacity, the liquid methane density under the atmospheric pressure boiling point could be selected as adsorption phase density to calculate the absolute adsorption capacity. Langmuir model can be used to explain the absolute adsorption capacity of methane under the high pressure isotherm adsorption.

Evaluation of the density and thickness of adsorbed methane in differently sized pores contributed by various components in a shale gas reservoir: A case study of the Longmaxi Shale in Southeast Chongqing, China

To investigate the densities and thicknesses of adsorbed methane in a shale gas reservoir, the Lower Silurian Longmaxi Shale in Southeast Chongqing was selected as a case study to establish models of the pore size distributions contributed by various components (PSDCVC), the amounts of methane adsorbed by various components (AMAVC) and the density and thickness of methane adsorbed by various components (DTMAVC). Based on the results of total organic carbon, carbon content in organic matter (OM), X-ray diffraction, methane isothermal adsorption and low-temperature nitrogen adsorption measurements, the pore size distributions and the amount of methane adsorbed by OM, clay and other minerals were calculated using the PSDCVC and AMAVC models. The average densities and thicknesses of adsorbed methane in pores with widths of <2 nm, 2–5 nm, 5–10 nm, 10–20 nm, 20–50 nm, 50–100 nm and 100–200 nm associated with OM, clay and other minerals under various conditions (i.e., temperatures of 30–70 °C and pressures of 1–10 MPa) were calculated using the DTMAVC model. The calculated data for the three analyzed samples using the PSDCVC and AMAVC models were compared with experimental results to determine the uncertainties of the two models. The density and thickness values of adsorbed methane in pores with various widths associated with OM, clay and other minerals decrease with increasing temperature and pore width and increase with increasing pressure. At the same temperature, pressure and pore width, the density and thickness values of adsorbed methane differ significantly among pores contributed by OM, clay and other minerals, exhibiting a decreasing trend from OM to clay to other minerals.

Evaluating methane adsorbed film densities on activated carbon in dynamic systems

Abstract Dynamic methane loading and discharge experiments on a 40 L adsorbed natural gas tank containing 20.5 kg of monolithic carbon adsorbent have been combined with pore volume data from subcritical nitrogen isotherms to evaluate the density and dynamic properties associated with adsorbed methane. The time-dependent density of the adsorbed gas was evaluated for narrow and wide micropores. The temperature-dependent adsorbed film volume was determined from the Ono-Kondo model and compared with the total micropore volume. The resulting adsorbed methane density evolves in two distinct parts. The density increases rapidly during the beginning of the loading process and increases slowly after narrow pores reach saturation. The narrow pores’ saturated adsorbed gas densities ranged from 0.26 – 0.35 kg/L, depending on the choice of film volume. The density of wide micropores was found to be highly dependent on the loading procedure due to the expected temperature dependence of the film volume. During discharge, it was found that the wide micropores deplete early while narrow micropores deplete slowly which causes the less than 100% efficient discharges seen in adsorbed natural gas systems. These density models have been applied to accurately predict the gravimetric excess adsorption of other carbon adsorbents at 35 bar and explain previously published pressure and temperature relations during tank loading.

Estimation of molecular column density of methane (XCH4) using AVIRIS-NG data

An attempt has been made to retrieve columnar density of methane (XCH4) over a suburban area of the Shadnagar in India from the high spatial and moderate spectral resolution (5 nm ± 0.5 nm) airborne visible/infrared imaging spectrometer next generation (AVIRIS-NG) data. The data collected were part of the joint airborne campaign by National Aeronautics Space Administration/Jet Propulsion Laboratory and Indian Space Research Organisation over several Indian sites during December 2015 to January 2016. The XCH4 was retrieved following the Moderate Resolution Imaging Spectroradiometer (MODIS) water vapor retrieval algorithm and was compared with the ground-based Fourier transform infrared (FTIR) observations. FTIR measured CH4 transmittance was fitted against Fast Atmospheric Signature Code3 (FASCODE3) simulated transmittance, and found their residual lies within ±1 % , which shows a very good retrieval sensitivity of FTIR. Hence FTIR observations are used for the validation of AVIRIS-NG derived XCH4 and found in good agreement. In the present study, we utilized airborne imaging radiance data in the CH4 absorbing channel at 2.365 ± 0.006 μm and nonabsorbing channels at 2.325 ± 0.006 μm and 2.365 ± 0.006 μm to compute atmospheric transmittance spectrum. Using a line-by-line radiative transfer algorithm, the XCH4 was estimated from AVIRIS-NG transmittance data. Prior to the application of the MODIS water vapor algorithm on AVIRIS-NG transmittance, it was also compared with the FASCODE3 simulated transmittance and found comparable. Study revealed that within the Shadnagar region, retrieved XCH4 varies little to moderate with an average of 9 × 1027 molecules cm − 2 with the highest value of 12 × 1027 molecules cm − 2 near the source region of the agriculture field. The study demonstrates the capability of AVIRIS-NG to quantify the column density of atmospheric species such as CH4 over a region.