Methane Desorption Research Articles

Investigation of enhancing multi-gas transport ability of coalbed methane reservoir by oxidation treatment

Subbituminous coal (Coal S) and anthracite coal (Coal A) were taken as the coal samples and H2O2, NaClO and ClO2 as the oxidants to investigate multi-gas transport ability enhancement of coalbed methane reservoir after oxidation. Thin section, dissolution rate and organic carbon content were measured to analyze the mechanism for different coal ranks and various oxidants. The dissolution rate of Coal A was greater than Coal S because large amounts of ferrous ions in Coal A had strong catalytic effect on Fenton reaction. However, there was large amounts of siderite composed of ferric ions in Coal S, which did not catalyze Fenton reaction. Meanwhile, the adsorption/ desorption behavior of both raw and treated coal samples was measured. Results show that, besides reaction between oxidants and organic matter/ pyrite/ clay minerals could destroy methane adsorption point in coals, weakening methane adsorption capacity. Also, the gas transport channels were widened and interconnected due to the oxidation dissolution and significant temperature increment during oxidation reaction. It is indicated that the reaction between coals and oxidants accelerated methane desorption, widened the methane mass transfer channel, and finally enhanced the methane multi-gas transport ability of methane in coal. The order of multi-gas transport ability enhancement by oxidation treatment under the condition of similar redox potential of oxidants was Coal ASFW > Coal AClO2 > Coal ANaClO > Coal AH2O2 and that of Coal S was Coal SSFW > Coal SH2O2 > Coal SNaClO > Coal SClO2.

Dynamic Fluid Interactions during CO2-Enhanced Coalbed Methane and CO2 Sequestration in Coal Seams. Part 1: CO2–CH4 Interactions

The injection of CO2 into coalbed methane (CBM) reservoirs to enhance methane recovery has a second desirable benefit in simultaneously sequestering CO2. However, the real-time dynamic evolution of native adsorbed and rejected non-adsorbed methane during the process of CO2-enhanced coalbed methane (CO2-ECBM) production remains poorly constrained as a result of the nonlinear and hysteretic response of both CO2–CH4 interactions (part 1) and CO2–H2O wettability (part 2) of the coal under recreated reservoir conditions. In part 1, we apply calibrated nuclear magnetic resonance (NMR) to explore mechanisms of methane desorption and CO2 replacement during multiple cycles of CO2-ECBM flooding under recreated in situ conditions. Results for contrasting sub-bituminous coal and anthracite indicate that the adsorbed methane sweep efficiency is improved by ∼16–26% with a single injection of CO2 over mere in situ desorption. Furthermore, CO2–CH4 displacement rates evolve during each CO2 injection cycle, first declining rapidly and then stabilizing with a long desorptive tail. Importantly, the cumulative methane sweep efficiency increases monotonically with successive cycles of CO2 injection, albeit at a reducing incremental efficiency, identifying the utility of cyclic CO2-ECBM as an effective method in both CO2 sequestration and enhanced gas recovery. Observed ratios of CO2 sorption capacities to CH4 recovery are 5.0 and 2.2 for sub-bituminous coal and anthracite, respectively, demonstrating an elevated potential for CO2 sequestration in sub-bituminous coals and more favorable CO2-ECBM recovery in anthracite, per unit mass of CO2 injected.

Resource Assessment and Numerical Modeling of CBM Extraction in the Upper Silesian Coal Basin, Poland

The paper presents the assessment of the resources of methane considered as the main mineral in the most prospective selected areas of the Upper Silesian Coal Basin, Poland in the region of undeveloped deposits. The methane resources were estimated by means of a volumetric method at three depth levels, 1000, 1250, and 1500 m. A part of the Studzienice deposit comprising three coal seams, 333, 336, and 337, located in a methane zone was chosen for the numerical modeling of simulated methane production. The presented static 3D model has been developed using Petrel Schlumberger software. The total resources of methane in the area amount to approximately 446.5 million of Nm3. Numerical simulations of methane production from the selected coal seams with hydraulic fracturing were conducted by means of Schlumberger ECLIPSE reservoir simulator. Based on the simulations, it was concluded that, in the first six months of the simulations, water is produced from the seams, which is connected with the decrease in the rock mass pressure. The process prompts methane desorption from the coal matrix, which in turn results in a total methane production of 76.2 million of Nm3 within the five-year period of the simulations, which constitutes about 17% of total methane resources (GIP). The paper also presents a detailed analysis of Polish legislation concerning the activities aimed at prospecting, exploring, and extracting the deposits of hydrocarbons.

Evolution of gas transport pattern with the variation of coal particle size: Kinetic model and experiments

Gas desorption laws varies with coal particle size. Their proper description is of great importance to natural gas engineering. This paper tries to summarize the internal links in commonly used models and combine them into a more general form. The combined general model is capable of describing fracture flow, matrix diffusion and surface sorption processes in pores with shapes like flat plates, cylinders and spheres. It can also be simplified into a power function which can be readily implemented into simulation of sorption and calculation of dynamic Fickian diffusion coefficients. Experiments including low-temperature liquid N2 adsorption, proximate analysis, isothermal methane sorption and desorption experiments with different particle sizes were conducted to validate the model. Other sorption data from literature were also collected for validation. The fitting results can help explain the size dependence of desorption characteristics and show the flow type evolutions during the damage of pore system.

Measurement and modeling of temperature evolution during methane desorption in coal

The decrease of coal temperature has been confirmed by many tests during methane desorption in coal, including coal and gas outburst, but the thermal-dynamic process for methane desorption has not been quantitatively studied. Therefore, firstly, the coal temperature and gas pressure are measured by temperature and pressure sensors in the process of methane desorption. Secondly, isosteric heats of adsorption are calculated according to the adsorption isotherm. Finally, heat transfer model is established and simulate the temperature evolution during methane desorption in coal under different conditions (initial temperature and gas pressure). The real tests and simulation results show that a lot of heat will be absorbed from coal as methane desorbing, which causes the coal temperature will go down by 5.5 K, and methane desorption is no longer isothermal process. In the initial stage of methane desorption in coal, the coal temperature will decrease sharply to an extremely low value, then slowly rise to the previous ambient temperature. And at the same ambient temperature, the higher the initial methane equilibrium pressure is, the larger the temperature at the coal body center drops in the process of methane desorption. In the coal body, the farther away from the wall of the coal sample canister, the more significant the decrease of the coal body temperature is, and the longer the time is to reach extremely low value, which is mainly due to the different heat transfer coefficients at different positions in the coal body. The total specific power, which is a key index in heat transfer model to simulate the change of coal temperature, sharply decreases during methane desorption, because the methane desorption quantity in unit time decreases gradually. This study has an important practical significance to reveal the evolution mechanism of coal and gas outburst, and predict outburst with temperature change as an index.

High-Pressure Methane Adsorption and Desorption in Shales from the Sichuan Basin, Southwestern China

Adsorbed methane is an important component of shale gas. Methane desorption, commonly ignored, can affect gas production. Gaining a better understanding of methane sorption in shale is important fo...

Simulation of Adsorption–Desorption Behavior in Coal Seam Gas Reservoirs at the Molecular Level: A Comprehensive Review

This work reviews the processes of methane (CH4) and carbon dioxide (CO2) adsorption and desorption, as well as the displacement of CH4 by CO2, at the molecular level. For the adsorbate, laboratory...

Pore morphology characterization and its effect on methane desorption in water-containing coal: An exploratory study on the mechanism of gas migration in water-injected coal seam

Water-injected technique was once considered as an effective way to solve the gas-induced problems in the mining industry, but has been stagnant due to its unstable conditions. A systematic knowledge on the micro-mechanism of water injection into coal seams is beneficial to better understand water-based techniques. However, the laboratory investigations considering the engineering background of water injection as well as the pore morphology of targeted coal seam have been rarely studied. In this paper, characterization of pore morphology and the effect of injected water on gas desorption characteristic were carried out using pore structure analyzers (N2 adsorption and mercury intrusion methods), high-resolution scanning electron microscopy and a home-made instrument (water-injecting desorption test). The pore morphology results from pore size distribution, fractal dimension, pore shape and connectivity indicate that the essential configuration of pore structure is well-developed larger pores containing abundant smaller pores with extensive distribution of constricted pores that are inaccessible to fluid migration. The influence of pore morphology on desorption process may be attributed to the microporous constrictions with non-effective pores, which are geometrically interpreted by pore blocking mechanism. The desorption test results show the total desorption volumes and initial effective diffusion coefficient have the reduce rates of 26.65% and 38% with the moisture content increasing from dry to 1.8% while have a little change as moisture increases (1.8%–11.2%), demonstrating the obstruction of water molecule on gas desorption pathway and the existence of extremity moisture content. Water injection has a remarkable effect on the average desorption rates in the initial period of 10 min; however, the ultimate desorption volume of 0.81 mL/g with higher moisture content of 11.2% is not sensitive to adsorption equilibrium pressure. Moreover, combined with the mature water-injected technique in the actual coal seam, a conceptual design was summarized to consider the effect of the constricted pore morphology on the interactions of “water-gas-coal”, which may demonstrate the micro-mechanism of gas migration in the far water-injected coal seam. Meanwhile, in the near water injection zone, due to more energetic gas molecules forming gas bubble in the aqueous condition, nucleation appears to be imagined to explain the pressure-insensitive phenomenon. These findings are of great guiding significance to the theoretical studies and field applications of actual water-injected coal seam.

Effects of moisture on methane desorption characteristics of the Zhaozhuang coal: experiment and molecular simulation

Coal and gas outbursts have occurred in the Zhaozhuang coal mine (a high gas coal mine) since its construction, and these outbursts pose a great threat to lives and property. Therefore, the combination of methane desorption experiments and molecular simulations was adopted to investigate the effects of moisture on the methane desorption characteristics of the Zhaozhuang coal, and the microscopic mechanism was analyzed in this paper. The aim of this work is to provide a method for predicting the effect of moisture on coal seam methane desorption, and quantitatively evaluating the control effect of hydraulic measures on coal and gas outbursts from a molecular perspective. The experimental data (methane desorption amount) were measured under various adsorption equilibrium pressures (0.3 MPa, 0.4 MPa, and 0.5 MPa) and moisture contents (0%, 5%, and 9.8%). Based on the Zhaozhuang coal molecular model, the molecular simulation process was conducted using Materials studio software, which can better match the experimental conditions by setting various pressure parameters (0.3 MPa, 0.4 MPa, and 0.5 MPa) and calculating various numbers of H2O molecules (0, 8, and 16) on the coal molecule. The results show that methane desorption decreases with the increasing moisture content in the experiment. The number of CH4 molecules adsorbed on the coal molecule decreases with the increasing number of H2O molecules in the simulation. This phenomenon can be explained by the competitive adsorption between CH4 and H2O molecule: the interaction between coal molecule and H2O molecules is stronger. The affinity between CH4 molecules and the coal molecule is reduced, and CH4 molecules are less aggregated around the coal molecule because of the presence of H2O molecules.

Effects of ambient pressure on diffusion kinetics in coal during methane desorption

To elucidate the influence of ambient pressure on diffusion kinetics during gas desorption, which is of great significance to the efficient development of coalbed methane, a methane desorption experiment was carried out on coal particles under different ambient pressures, and diffusion coefficients for each test time were solved by the unipore diffusion model. The experiment was carried out using our independently developed 'coal particle methane desorption meter' to overcome the difficulty that the existing equipment could not achieve a constant ambient pressure higher than atmospheric pressure. The results show that during methane desorption in coal particles, the diffusion coefficient was not constant but gradually decreased with time, showing a power function relationship. In addition, the diffusion coefficient decreased linearly with increasing ambient pressure, and the degree of influence was related to time. This research will play an important role in improving the unipore diffusion model and elucidating the gas production mechanisms. [Received: February 2, 2018; Accepted: May 9, 2018]

Effects of ambient pressure on diffusion kinetics in coal during methane desorption

To elucidate the influence of ambient pressure on diffusion kinetics during gas desorption, which is of great significance to the efficient development of coalbed methane, a methane desorption experiment was carried out on coal particles under different ambient pressures, and diffusion coefficients for each test time were solved by the unipore diffusion model. The experiment was carried out using our independently developed 'coal particle methane desorption meter' to overcome the difficulty that the existing equipment could not achieve a constant ambient pressure higher than atmospheric pressure. The results show that during methane desorption in coal particles, the diffusion coefficient was not constant but gradually decreased with time, showing a power function relationship. In addition, the diffusion coefficient decreased linearly with increasing ambient pressure, and the degree of influence was related to time. This research will play an important role in improving the unipore diffusion model and elucidating the gas production mechanisms. [Received: February 2, 2018; Accepted: May 9, 2018]

Experimental Study on Desorption Characteristics of Coalbed Methane under Variable Loading and Temperature in Deep and High Geothermal Mine

Due to the influence of deep high stress, geothermal heat, and other factors, the law of desorption of methane in coal seams is more complicated in the process of mining deep coal seams, which is prone to methane over‐limit, coal and gas outburst, and other accidents. In order to study the desorption characteristics of coalbed methane under different loading and temperature conditions, the desorption tests at different deformation stages of coal containing methane were carried out in the process of loading‐adsorption‐desorption‐reloading until the coal sample was destroyed by using the seepage‐adsorption‐desorption test system on coal and rock mass, and the test programs were different combinations of gas pressure 1.2 MPa, two kinds of confining pressure, and three kinds of temperature. The results show that the cumulative methane desorption amount corresponding to each deformation stage presents a convex parabolic increase trend with the increase in desorption time, while the desorption rate presents a power function decay trend. Under the condition of the same desorption time, the cumulative methane desorption amount from large to small is residual deformation stage, compaction stage, near the peak stress, plastic deformation stage, and elastic deformation stage. Under the same confining pressure, temperature, and methane pressure, the maximum desorption rate from large to small is residual deformation stage, near the peak stress, plastic deformation stage, compaction stage, and elastic deformation stage. The desorption and diffusion of methane are promoted under the higher temperature and lower confining pressure, which presents a certain mechanism of promoting desorption. The thermal movement of methane molecules is intensified with the increase in temperature, and the adsorption effect between methane molecules and the molecules at the surface of the coal is weakened. The cumulative methane desorption amount and the maximum desorption rate increase with the increase in temperature. The cumulative methane desorption in the residual deformation stage is obviously greater than that in other deformation stages. The increase in confining pressure inhibits the development and expansion of pore fractures in raw coal specimen and hinders the increase in the effective desorption surface area. The cumulative methane desorption amount and the maximum desorption rate decrease with the increase in confining pressure.

Влияние естественной влажности на характерное время десорбции метана из углей различной степени метаморфизма

Goal. To study the effect of natural internal moisture content on the kinetics of methane desorption from coals of varying degrees of metamorphization. Methodology. For the research, coal was used after a long (more than 100 days) preliminary exposure in a dry, closed indoors. The measurements were carried out on several samples of Donbass coals with different volatile content. Two groups of coal samples were used - dry, with natural internal humidity and one sample with artificial humidity of 1.5%. The volumetric method was used for measurements. The method includes three stages: 1st  saturation of coal with compressed methane, 2nd  preliminary discharge of compressed gas from a container with coal after its saturation, and 3rd  collection of methane released by coal into a storage vessel. Before registration of desorption, pressurized gas was discharged from the free volume of containers into the atmosphere. The desorption unit contains a low-temperature trap (78°C) for water vapor and a warming radiator for methane entering the storage vessel. To determine the numerical values of the characteristic time of desorption of methane from coal, we used information on the change in gas pressure in the storage vessel during desorption. To analyze the results, a method based on the concept of a change in the characteristic relaxation time of desorption during methane emission was used. Results. Experimental results show that in wet coals the ratio between the amount of methane in coal and the intensity of its outflow at any desorption site is less than in dry coals. It was found that in coals of the metamorphic series the presence of natural moisture leads to a decrease in the intensity of methane emission, a decrease in the characteristic desorption time and a decrease in the activation energy of methane desorption by 0.4 - 2.5 kJ / mol. The features of the kinetics of desorption indicates competition energetics of interactions between methane and water with the surface of the pores of coal. Scientific novelty. It was found that even without artificial humidification, but in the presence of natural internal moisture in coal, the degassing time during desorption is reduced (in comparison with dry coal). Practical significance. The research results can be used to optimize the duration of hydraulic saturation of the coal seam and the water consumption during coal degassing.

Tests to Ensure the Minimum Methane Concentration for Gas Engines to Limit Atmospheric Emissions

During the extraction of hard coal in Polish conditions, methane is emitted, which is referred to as ‘mine gas’. As a result of the desorption of methane, a greenhouse gas is released from coal seams. In order to reduce atmospheric emissions, methane from coal seams is captured by a methane drainage system. On the other hand, methane, which has been separated into underground mining excavations, is discharged into the atmosphere with a stream of ventilation air. For many years, Polish hard coal mines have been capturing methane to ensure the safety of the crew and the continuity of mining operations. As a greenhouse gas, methane has a significant potential, as it is more effective at absorbing and re-emitting radiation than carbon dioxide. The increase in the amount of methane in the atmosphere is a significant factor influencing global warming, however, it is not as strong as the increase in carbon dioxide. Therefore, in Polish mines, the methane–air mixture captured in the methane drainage system is not emitted to the atmosphere, but burned as fuel in systems, including cogeneration systems, to generate electricity, heat and cold. However, in order for such use to be possible, the methane–air mixture must meet appropriate quality and quantity requirements. The article presents an analysis of changes in selected parameters of the captured methane–air mixture from one of the hard coal mines in the Upper Silesian Coal Basin in Poland. The paper analyses the changes in concentration and size of the captured methane stream through the methane capturing system. The gas captured by the methane drainage system, as an energy source, can be used in cogeneration, when the methane concentration is greater than 40%. Considering the variability of CH4 concentration in the captured mixture, it was also indicated which pure methane stream must be added to the gas mixture in order for this gas to be used as a fuel for gas engines. The balance of power of produced electric energy in gas engines is presented. Possible solutions ensuring constant concentration of the captured methane–air mixture are also presented.

Wettability modification and its influence on methane adsorption/desorption: A case study in the Ordos Basin, China

AbstractWettability modification of coal rock may cause serious change in the methane adsorption/desorption behaviors. Thus, the contact angle measurement and isothermal adsorption/desorption experiment of raw coal and samples treated with surfactants (STS) were conducted to investigate the wetting properties and methane adsorption/desorption characteristics. The results indicated that the long‐flame coal (LFC) has the good hydrophilicity itself, and there was no evident sign of saturated adsorption for different samples at relatively low‐pressure (<8 MPa) stage. The sample treated with the wettability reversal agent (G502) had the larger methane adsorption capacity than the wetted samples (LAS, JFC, and 6501), with the latter facilitating the methane desorption. Additionally, the adsorption capacity of the air‐dried samples was stronger than that of the water‐containing samples, including the moisture‐equilibrated, LAS, JFC, and 6501, reflecting that the better the hydrophilicity, the weaker the methane adsorption. Besides, the desorption hysteresis rate of the same sample was mainly controlled by pressure, i.e. the desorption hysteresis indicated a logarithmic decrease with the increasing pressure, but the STS clearly showed the desorption hysteresis to varying degree due to the wettability differences. The pressure drop in the low‐pressure stage was difficult to drive the adsorbed methane to immediately desorb from the matrix surface, whereas even caused further adsorption or re‐adsorption, meaning that the coal required a greater depressurization to enter the effective desorption stage. Finally, the positive implications of wettability modification including enhancing CBM recovery, as well as coal and methane outburst prevention and coal dust control in the mining industry were discussed.

Laboratory measurements of methane desorption behavior on coal under different modes of real-time microwave loading

This paper presents a technique for accelerating coalbed methane (CBM) desorption to increase extraction efficiency using microwaves. Methane desorption experiments with and without real-time microwave loading (ML) were carried out in the laboratory. To avoid high temperatures in the samples, ML was employed via two modes; continuous ML (CML) with low power and discontinuous ML (DML) with high power. The results show that total desorption volumes were increased from 1.87 to 3.26 times under CML and from 1.91 to 4.13 times under DML. The desorption rate using CML decreased smoothly like the rate without ML but the desorption rate was higher. The DML caused the desorption rate to increase rapidly and sharp peaks were evident on its desorption rate graph. For DML, the maximum desorption rate increased by a factor of 10.8. Kinetic analysis indicated that both CML and DML increased the diffusion coefficient and reduced diffusion attenuation. For the same microwave output energy, DML with short-term microwave bursts with high power has a better stimulating effect on methane desorption than CML. That ML significantly enhances methane desorption indicates that ML can greatly improve CBM productivity, and thus it has the potential to become a new CBM stimulation technology.

Optimum oxidation temperature of coal bed for methane desorption in the process of CBM extraction

To explore the optimum oxidation temperature of coalbed for promoting methane desorption, this paper carried out the experiments based on the self-built coal oxidation heating system in different gaseous environments and the high-temperature and high-pressure gas adsorption instrument. Besides, the effect of methane on free radicals and surface functional groups at the optimum oxidation temperature was studied by using electron spin resonance (ESR) spectrum and Fourier transform infrared spectroscopy (FTIR). The results show that the residual methane is the lowest at the oxidation temperature of 80 °C, indicating that 80 °C is the optimum oxidation temperature for CBM extraction. At 80 °C, the inhibitory effect of methane on the reactivity of coal is stronger and the reactivity can also increase. At low concentration (<25%), the inhibitory effect of methane on the oxidation reaction of aliphatic hydrocarbon is poor. And the inhibitory effect can be improved by oxidizing and heating coal to 80 °C. At 80 °C, the inhibitory effect of methane on –OH oxidation is stronger at low methane concentration. Meanwhile, the concentration range of methane inhibiting –OH oxidation can be expanded by oxidizing and heating coalbed to 80 °C. The inhibitory effect of methane on –COOH oxidation mainly occurs when methane concentration is high. The concentration can be lowered when coalbed is oxidized and heated to 80 °C. –C–O group can be formed only when methane concentration exceeds a certain value, but this initial methane concentration can be lowered when coalbed is heated up to 80 °C through oxidation.

Research and Development of Bio-Degasification Technologies for Coal Fields

The current situation and development trends in the biological degasification of coal are reviewed. It is shown that methane desorption is a consequence of rock mass destruction by activity of microorganisms and releasing bacterial metabolites. The influence of microorganisms on coal as a function of a prevailing microbial community and its variety, access of oxygen and nutritious substrates is observed. Advancement of the biological method for coal field degasification based on the methanotrophy is discussed.

Modeling permeability variation in coal seams during active desorption of methane and flow of formation fluid

Modeling permeability variation in coal seams during active desorption of methane and flow of formation fluid

Effect of rock mineralogy on Hot-CO2 injection for enhanced gas recovery

Conventional gas reservoirs are one of the viable options for CO2 enhanced gas recovery and sequestration. Injection of hot CO2 into depleted reservoirs is expected to improve gas recovery. Static adsorption and core flooding experiments were performed to quantify methane/CO2 adsorption/desorption using different rocks at different temperatures and pressures. Rocks such as shale, tight sandstone, calcite, and dolomite were used. For calcite, theoretical simulations were performed. Though methane desorption has increased when the temperature was raised, the results suggest that the gas recovery has doubled when the temperature has been increased from 50° to 100 °C in conventional reservoirs and from 100° to 150 °C in conventional and unconventional reservoirs. Similar trends were obtained for different rocks with increasing temperature. Core flooding and static adsorption experiments showed matching results. Rock mineralogy affects the adsorption capacity of the rock with shale rock having a 60% higher methane production than sandstone.