Methane Desorption Research Articles

Experimental Assessment of Combined Contribution of Coal Mass Diffusion and Seepage to Methane Migration under In Situ Stress Conditions

Gas diffusion and seepage characteristics can reflect the transport capacity of coal mass pores and fracture channels and are also important parameters to determine the mechanism of methane migration. Currently, research on the contribution of diffusion and seepage to methane migration is carried out mainly by fixing one parameter and discussing the effect of the other. However, few studies are focused on the dynamic combined effect of diffusion and seepage on methane migration under in situ stress conditions, which is mainly attributed to difficulties in obtaining the parameters of diffusion characteristics of coal mass under stress. This paper presents a study on the dynamic combined effect of coal mass diffusion and seepage on methane migration under different in situ stress conditions. First, the physical structure model of coal mass under high and low stresses was constructed based on the variations of coal mass porosity, permeability, and computed tomography under different stresses. Meanwhile, based on the methane desorption and diffusion curves of coal mass under different stresses, the diffusion parameters of coal mass were obtained according to the corresponding diffusion model. Furthermore, the coupled multifield model was used to calculate the methane migration in coal mass during the process of borehole extraction with different stresses. The results suggest that the difficulty in methane extraction is directly proportional to the stress, but a huge discrepancy exists in methane migration under high and low stresses principally due to the change of dominant factors in methane migration of coal mass under different stresses. Additionally, given the essential factors controlling the overall methane migration of coal mass under high and low stresses, a joint technical method for promoting methane flow rate under multicoal seam conditions in the same mining area was proposed, i.e., hydraulic fracturing and sand injection (increasing permeability) in coal seams under low stress and simultaneous application of hydraulic fracturing and sand injection and multistage cavitation pressure relief (increasing diffusion) in coal seams under high stress. The research results obtained in this paper provide theoretical support for understanding the methane migration mechanism in coal seams under in situ stress and stimulated gas production.

Experimental Evaluation of Working Fluid Damage to Gas Transport in a High-Rank Coalbed Methane Reservoir in the Qinshui Basin, China.

Formation damage induced by the injected working fluid runs through the whole life cycle of coalbed methane (CBM) extraction and ultimately reduces the production of CBM wells. The conventional method uses permeability as a parameter to evaluate the formation damage severity to coal by working fluids containing solids. However, less attention has been attracted to the formation damage of the pure liquid phase of the working fluid on the multiscale gas transport process of CBM. Therefore, we present a multiscale working fluid filtrate damage evaluation method considering the desorption, diffusion, and seepage and use it to evaluate high-rank coal in the Qinshui Basin of China. The results show that pure liquids with different pH values and salinities significantly damage the desorption-diffusion and seepage ability of CBM. The damage rates of alkaline fluid, hydrochloric acid fluid, and clear water on the methane desorption capacity of coal are 63.64, 17.63, and 24.34%, respectively, while those on the permeability of coal are 29.88, 42.38, and 46.66%, respectively. The formation damage severity in the seepage process is higher than that in the desorption-diffusion process, which proves the necessity of multiscale working fluid damage evaluation on CBM. Effective channel reduction and resistance increase in gas transport are the mechanisms of working fluid filtrate-induced formation damage, which are caused by water blocking, sensitive mineral swelling and clogging, and strengthened stress sensitivity. In addition to controlling the solid damage of the working fluid, reducing the invasion of the working fluid filtrate and maintaining its compatibility with the coal and formation fluids are even more important to protect the coal reservoir.

Plasma-Induced Desorption of Methane and Carbon Dioxide over Silico Alumino Phosphate Zeolites

Plasma-Induced Desorption of Methane and Carbon Dioxide over Silico Alumino Phosphate Zeolites

The quantitative study of methane adsorption on the Pt(997) step surface as the initial process for reforming reactions

The adsorption states and thermal process of methane on a stepped Pt surface were investigated using temperature-programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), and density functional theory (DFT) calculations including van der Waals interactions. By estimating the activation energies of methane desorption from the TPD data, it was revealed that the adsorption energy for methane on the step site (0.19 eV) was higher than that on the terrace site (0.15 eV). The IRAS spectrum after multilayer adsorption and subsequent 70 K heating showed two peaks at 3009 and 1305 cm−1, which were assigned to the antisymmetric stretching and the deformation modes for adsorbed methane on the step site, respectively. The present DFT calculations show that the most stable adsorption structure for methane on the step site is a “2H” structure, where two C-H bonds point toward Pt atoms. Based on the electronic structure analysis, we conclude that the stability of the 2H structure originates from the mixing between the methane molecular orbitals and the orbitals of step Pt atoms. As a result, the length of the C-H bond pointing toward the Pt step atom is elongated compared with that of other C-H bonds. Thus, the Pt step site already activates the adsorbed methane slightly.

Interaction between slick water and gas shale and its impact on methane desorption: a case study of Longmaxi member shale formation in the northeast of Chongqing, China

Well shut-in time significantly affects the production performance of shale-gas-well. However, interaction between shale powders and fracking fluid on methane desorption has been rarely reported. In this work, based on the volume method following Boyle’s law under higher pressure, the experimental setup was conducted to obtain the adsorption and desorption isotherms to explore the effect of different shut-in times (including 0, 1, 3, 5, 10, and 30 days) on methane desorption. We fitted the methane adsorption and desorption isotherms by the Freundlich model, and the results show that the interaction can obviously impact desorption isotherm, desorption efficiency and adsorbed phase methane content. The inflection points of the constant k and n reduction curves, desorption efficiency reduction curve and adsorbed gas content reduction curve all occur when the interaction time is to 10 days, indicating that 10 days is the best value for the interaction between slick water and gas shale. The results provide an essential supplement that can help elucidate the impact of shut-in time on gas-shale-well production performance experimentally.

Lab‐Scale Investigation of Slickwater Impact on Methane Desorption on Longmaxi Gas Shale

AbstractAfter multistage hydraulic fracking, a huge amount of slickwater stuck in shale gas formation significantly affects the shale‐gas‐well production performance. A set of comparative experiments to illustrate slickwater and its chemicals' impact on the methane desorption on shale powders were performed. The influence of slickwater and its chemicals on desorption isotherm, desorption efficiency, and adsorbed phase methane content as well as cumulative gas production was analyzed. The findings reflect the synthetic slickwater impact on methane desorption on shale powders, indicating that it can be helpful to optimize slickwater formulation and design shale‐gas‐well bottom flow pressure to obtain higher gas production. Also, the observations and analysis give a supplement for improving shale gas recovery through studying the function of chemical additives in slickwater on methane desorption.

Modeling Dynamic Gas Desorption in Coal Reservoir Rehabilitation: Molecular Simulation and Neural Network Approach.

A thorough understanding of the control mechanisms of coal reservoir modification on methane adsorption and desorption is essential as this is a key technique for increasing the effectiveness of gas extraction. In this study, molecular dynamics simulations and neural networks were used to evaluate the effects of several coal reservoir alteration factors on gas desorption, from both microscopic and macroscopic perspectives. The findings demonstrated a direct correlation between coal pore size and the amount of methane adsorbed, as well as an inverse relationship between coal pore size and methane adsorption capacity and energy. The different methane-repelling properties of CO2, N2, and H2O, which are frequently used in coal reservoir reforming, are primarily due to the different diffusion capabilities of these three gases. The best reservoir reforming effect can be obtained by setting the pressure ratio of CO2 to N2 to 3.4:6.6. The thickness, depth, gas content, height, advance speed, rate of extraction, and daily production of coal are all closely interrelated, enabling a more accurate assessment of gas gushing.

Thermal recovery of offshore coalbed methane reservoirs: Flow characteristics of superheated steam in wellbores

Methane in coalbed methane (CBM) reservoirs is mainly in the adsorbed state, and has both free and dissolved states. The proportion of adsorbed methane can be as high as 90% or more. Field practice shows that low methane desorption efficiency is one of the keys affecting CBM development. The adsorption of methane is significantly affected by temperature, and the desorption efficiency increases with the increase of temperature. In this paper, the wellbore flow during the development of CBM reservoirs by injection of superheated steam is taken as the research object, and the superheated steam flow model is established considering the influence of seawater disturbance caused by the phase change of superheated steam. The study found: (a) In the formation section wellbore, the superheated steam has the highest temperature value. (b) The temperature of the superheated steam is affected by both the Joule Thompson effect and the heat loss effect. (c) The longer the wellbore in the seawater section, the lower the temperature of the superheated steam in the wellbore. (d) Superheated steam is only suitable for shallow sea conditions.

Natural Gas Storage Filled with Peat-Derived Carbon Adsorbent: Influence of Nonisothermal Effects and Ethane Impurities on the Storage Cycle.

Adsorbed natural gas (ANG) is a promising solution for improving the safety and storage capacity of low-pressure gas storage systems. The structural-energetic and adsorption properties of active carbon ACPK, synthesized from cheap peat raw materials, are presented. Calculations of the methane-ethane mixture adsorption on ACPK were performed using the experimental adsorption isotherms of pure components. It is shown that the accumulation of ethane can significantly increase the energy capacity of the ANG storage. Numerical molecular modeling of the methane-ethane mixture adsorption in slit-like model micropores has been carried out. The molecular effects associated with the displacement of ethane by methane molecules and the formation of a molecule layered structure are shown. The integral molecular adsorption isotherm of the mixture according to the molecular modeling adequately corresponds to the ideal adsorbed solution theory (IAST). The cyclic processes of gas charging and discharging from the ANG storage based on the ACPK are simulated in three modes: adiabatic, isothermal, and thermocontrolled. The adiabatic mode leads to a loss of 27-33% of energy capacity at 3.5 MPa compared to the isothermal mode, which has a 9.4-19.5% lower energy capacity compared to the thermocontrolled mode, with more efficient desorption of both methane and ethane.

Real-time monitoring of induced strain during multi-stage ad-/desorption of methane on coal

Real-time monitoring of induced strain during multi-stage ad-/desorption of methane on coal

Simulation study on dynamic characteristics of gas diffusion in coal under nitrogen injection

To reveal the mechanism of desorption of methane in coal seams by inert gas N2, the desorption behavior of CH4 after N2 injection was studied by using Giant Canonical ensemble Monte Carlo (GCMC) and Molecular Dynamics (MD) methods with wiser bituminous coal as the research object. The results show that the adsorption isotherms of CH4 and N2 in the molecular structure model of bituminous coal are in good agreement with the Langmuir adsorption isotherm model. The adsorption capacity of the two gases in the bituminous coal structure model is CH4 > N2. The higher the N2 injection pressure, the higher the temperature, and the more methane desorption. N2 can replace some adsorbed CH4 through competitive adsorption with CH4. Compared with injecting high-temperature nitrogen to desorb methane in coal seams, in high-pressure nitrogen, the diffusion effect of CH4 flowing in coal is more significant. The higher the nitrogen injection pressure, the better the effect of N2 promoting CH4 desorption. The relative concentration of CH4 in the vacuum layer gradually increases with the increase of water content. This indicates that the water in coal promotes the desorption of CH4. The mechanism of N2 injection and CH4 desorption in coal seams mainly includes gas displacement and gas dilution and diffusion. This study provides theoretical support for methane extraction technology in goaf.

Study on the behavior and mechanism of methane desorption-diffusion for multi-scale coal samples under multi-temperature conditions

• Obvious methane release by thermal in large specimen and low pressure. • More activation energy is required for methane diffusion in columnar coal. • Methane diffusion from coal matrix to the fracture is enhanced by thermal action. • Pressure-depleted reservoirs of CBM extraction could be improved by thermal action. Based on the background of coalbed methane thermal mining and mine gas control, this paper mainly investigates the effect of thermal action on the enhanced methane desorption-diffusion characteristics of multi-scale coal samples under different conditions and the corresponding mechanism through a series of methane dispersion experiments and theoretical analysis. The results show that the relationship between temperature and diffusion coefficient can be described by the modified Arrhenius equation, and the activation energy required for gas diffusion in columnar coal is greater than that in granular coal; The diffusion coefficient decreases linearly with increasing adsorption pressure under non-thermal action, while the pressure-dependent diffusion coefficient variation relationship under thermal action can be described by a quadratic function; The variation law of diffusion coefficient with coal size can be explained in terms of pore distribution and effective diffusion cross-sectional area in coal. In addition, the concept of “extreme particle size” has been used to explain the significant size effect exhibited by methane desorption, and the extreme particle size of the coal sample used in this experiment is inferred to be about 1 mm. Thermal action has a significant enhanced effect on methane release in large size coal samples and at low adsorption pressure. For low-pressure reservoirs, applying appropriate thermal measures to stimulate the coal matrix can significantly promote residual methane desorption, more importantly, enhance the diffusion ability of methane from coal matrix to the fracture, increasing the matrix methane diffusion flux, which is expected to improve the capacity performance of pressure-depleted reservoirs in the middle and late stages of CBM extraction, thus achieving efficient recovery of CBM. This study has improved gas transport theory in porous media to a certain extent, and also provides a certain theoretical basis for CBM thermal mining and gas disaster prevention and control.

Molecular simulations on the continuous methane desorption in illite nanoslits

A molecular dynamics workflow to simulate the desorption–extraction of shale gas is proposed for predicting the production of shale gas. • A novel desorption–extraction MD workflow based on the EF-NEMD is proposed. • Some factors affecting the recovery are examined. • Large amount of methane in micropores is unrecoverable due to the stronger adsorption. • The recovery decline curves could be obtained in the proposed MD workflow. • Models of enhancement of recovery by pressure difference and temperature are built. Understanding microscopic process of gas desorption is important to production forecast in shale gas development. In usual simulations on the gas desorption process, the desorption occurs in a non-equilibrium state, but stops when the desorption–adsorption equilibration is reached. This is contrary to the continuous process in gas production. A workflow based on non-equilibrium molecular dynamics (NEMD) is proposed in this work to simulate the continuous desorption in the illite nanoslits by introducing an intermittent extraction into the whole process. A production curve is obtained in the workflow, and a pseudo decline-curve analysis (PDCA) can be provided in molecular simulation. The variation of desorption–extraction with pore size ( H ), temperature ( T ) and pressure difference ( ΔP ) is discussed. The attraction of illite–methane in the narrower slits is stronger than that in the wider slits. In the early stage, the extraction is dominated by the free gas in the wider slits. And in the later stage, the desorption of adsorbed gas in the narrower slits is the main process. The ΔP and T promote the desorption and extraction mainly in the early stage. The ΔP promotes the desorption in the wider slits more remarkably, while the desorption in the narrower slits is enhanced more by a higher T . The enhancement of desorption by ΔP and T in the early stage is modeled. The newly developed MD workflow and obtained PDCA model can be readily extended to study the extraction and production prediction of shale gas.

Belt-like In2O3 based sensor for methane detection: Influence of morphological, surface defects and textural behavior

Herein, gas sensors based on mesoporous belt-like In2O3 products derived from a single-step electrospinning method were produced, and the influence of the annealing temperature on their sensing performance was evaluated. A detailed comparison of the morphology, surface defects and textural behavior of the belt-like In2O3 products was carried out to understand the observed gas sensing trends. The In2O3 sensor produced at an annealing temperature of 550 ℃ displayed improved sensing capabilities with a response of 1.1 to 90 ppm of methane at a lower operating temperature of 100 ℃. The response and recovery times of this sensor were only 36 and 44 s, respectively, and it displayed good stability and selectivity as well as a lower detection limit of 0.18 ppm. Experimental characterization revealed that this enhanced sensing behavior originate from the mesoporous nature of belt-like In2O3 products composed of small-sized particles which offered a large number of active sites for methane gas molecules as a result of the high surface area and high concentration of oxygen vacancies, which enabled greater channels for methane gas adsorption and desorption capacity.

Catalytic performances in methane combustion over Pd nanoparticles supported on pure silica zeolites with different structures

Catalytic combustion of CH4 to CO2 and H2O was studied over Pd nanoparticles supported on different siliceous zeolites (MFI, BEA and CHA) with γ-Al2O3 as the reference support, and it was found that as supports, zeolites exert remarkable influence on the catalytic performance of methane oxidation, with the Pd catalyst (1 wt% loading) supported by siliceous MFI (ZSM-5-Si) presenting the highest activity. Over the exceptional catalyst, a complete conversion of methane can be achieved at around 380 °C, which is about 120 °C lower than the temperature needed for the Pd nanoparticles supported on γ-Al2O3 (Pd/γ-Al2O3), one of the best catalysts for the methane combustion. Physicochemical characterizations including X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), temperature programmed desorption of methane (CH4-TPD) and temperature programmed reduction of methane (CH4-TPR) techniques were used to acquire an idea what is behind the discrepancy in the catalytic performances of methane combustion over these Pd-based catalysts. Based on these results, it is proposed that the different methane adsorption and the oxygen migration capability are mainly related to the difference in the catalytic performances of methane combustion over these catalysts. Among these factors, the difference in the methane adsorption is critical for the different catalytic performances, as evidenced by the kinetic measurements.

Enhancement of multi-gas transport process in coalbed methane reservoir by oxidation treatment: Based on the change of the interaction force between coal matrix and gas molecules and knudsen number

Anthracite coal of Zhijin Block was taken as the coal samples and NaClO as the oxidants to investigate enhancement of multi-gas transport process in coalbed methane reservoir by oxidation treatment. Industrial microscope observation, SEM observation, low-temperature N2 sorption measurement and NMR test were used to comprehensively characterize the multiscale pore structure of coal. The change of macromolecular structure of coal before and after oxidation treatment was tested by 13C NMR test, and the force between coal matrix and gas molecules was estimated. Based on the pore size distribution of coal obtained by NMR analysis, the Knudsen number was calculated. Oxidation treatment effectively promoted the desorption of methane in coal, increased the content of free methane in coal. It also led to the CBM gas well entering the stable production period earlier, and shortens the gas breakthrough time of the gas well. Oxidation treatment improved micropores to larger pores by dissolving the coal matrix, and the porosity and permeability of coal were increased. Oxidation treatment led to the widening of pore diameter, and the effect of Knudsen diffusion on the core seepage of the matrix was gradually enhanced. Macroscopically, the gas slippage effect was more significant and the permeability was enhanced. The mechanism of oxidation treatment on multi-gas transport process was mainly reflected in two aspects: increasing the content of free methane and enhancing the gas supply capacity of coal.

CBM Desorption Model and Stages Based on a Natural Desorption Experiment.

Coalbed methane (CBM) desorption modeling is critical for understanding CBM desorption mechanisms and objectively analyzing the production characteristics of CBM wells. According to the CBM natural desorption experimental data of 64 coal samples taken from the Qinshui Basin, we established a CBM desorption model, quantitatively identified the CBM desorption stages, and discussed the relationship between CBM desorption characteristics and well productivity. The results indicated a very significant functional relationship between the CBM natural desorption time and cumulative desorption quantity, which could be accurately described by the model V = aLt/(t + bL). On the basis of this model and the numerical description of the desorption data, the CBM natural desorption process was divided into four stages: the desorption startup stage, desorption sensitive stage, desorption steady stage, and desorption decay stage. As indicated by analogical reasoning of the CBM well production process, the desorption startup stage corresponded to the drainage-based pressure drop stage, the desorption sensitive and steady stages corresponded to the steady production stage, and the desorption decay stage corresponded to the production declining stage. The CBM adsorption time exponentially decreased with the increase in the average CBM desorption rate and with the increase in the CBM gas content and vitrinite/inertinite ratio. Furthermore, within a certain range of desorption pressure, a high ratio between the adsorption time and gas content corresponded to the extension of the steady production stage of CBM wells, whereas higher or lower ratios were adverse to steady production.

Relationship between desorption amount and temperature variation in the process of coal gas desorption

Coal bed methane (CBM) is a clean energy source and its main component is methane, however, due to the complex conditions of its occurrence, its content detection is inaccurate and its utilization is not efficient. To further investigate the desorption and diffusion of methane in coal seams, this study uses an experimental system to investigate the desorption volume and temperature variations of gas desorption at different equilibrium pressures for three different particle sizes of coal samples. The results show that the desorption process is a heat absorption and cooling process, which is mainly influenced by the equilibrium pressure and the particle size of the coal samples. The amount of desorption and the absolute desorption temperature variation increases with increasing equilibrium pressure and increases with decreasing particle size of the coal sample. The desorption temperature variation at a desorption time of approximately 3000 s is close to the minimum. There is a linear relationship between the gas desorption volume and the absolute desorption temperature variation, which can be used to predict the desorption volume using the absolute desorption temperature variation. This will assist in the accurate measurement of coal bed methane content and the prevention and control of coal mine gas disasters.

Methane Adsorption and Desorption on a Deep Shale Matrix under Simulative Reservoir Temperature and Pressure

Methane Adsorption and Desorption on a Deep Shale Matrix under Simulative Reservoir Temperature and Pressure

Study on the dynamics mechanism of methane diffusion in coal under microwave heating

To study the effects of microwave on the methane desorption characteristics of coal, the structural parameters of Pingdingshan coal were obtained through X-ray diffraction (XRD) and mercury intrusion test. Then the coal molecular structure models were established. The adsorption of CH4 was simulated using Materials Studio. Finally, the combination of methane desorption experiments and molecular simulations were adopted to investigate the effects of microwave on the methane desorption characteristics, and the microscopic mechanism was analyzed. The results show that: the effect of microwave on the structure of coal is mainly reflected in the change of crystallite diameter (La). For the macro perspective, the average pore diameter, total pore volume, porosity and permeability of the coal increase and the total specific surface area decreases after microwave heating. Microwave heating leads to the decrease in adsorption pores, the increase in percolation pores and microfractures, and the enhancement of inter-pore connectivity. The simulated transport diffusion coefficients were in good accordance with the methane desorption experimental results, indicating that microwave heating helps methane to diffuse out of the coal.