Methane Desorption Research Articles

Some parameters of coal methane system that cause very slow release of methane from virgin coal beds (CBM)

In some worldwide hard coal basins recovery of methane from virgin coal beds is difficult. In general, mentioned difficulties are related to geo-mechanical, petrographical and physical-chemical properties of coals in question, occurring for example in the Bowen Basin (Australia) or the Upper Silesian Coal Basin (Poland). Among numerous properties and parameters, the following are very essential: susceptibility of coal beds to deformation connected with coal stress state change and contemporary shrinkage of the coal matrix during methane desorption. Those adverse geo-mechanical and physical-chemical effects are accompanied by essential change of the porous coal structure, which under these disadvantageous conditions is very complex. This study aims to show difficulties, which occur in phase of recognition of the methane-reach coal deposit. Volume absorbed methane (not surface adsorbed) in sub-micropores having minimal size comparable with gas molecule diameter must possess energy allowing separation of the nodes and methane release to micropores.

Characteristics of pore structure and fractal dimension of low-rank coal: A case study of Lower Jurassic Xishanyao coal in the southern Junggar Basin, NW China

In this study, a series of laboratory experiments were performed to firstly analyze the characteristics of the pore structure in low-rank coal (Ro<0.70%), and then relationships between fractal dimensions and coal rank, coal composition and pore structure, and their impacts on methane adsorbability and seepage ability were studied too. The desorption isotherms of low-rank coal mainly belongs to Type B, which are primarily caused by ink-bottle-shaped and narrow-slit pores that are good for coalbed methane (CBM) enrichment, but bad for seepage. The seepage pores are dominated by primary plant macropores (>1000nm), with a poor development of mesopores (100–1000nm). The fractal features of adsorbed pores and seepage pores were defined and calculated using fractal dimensions D2 (2.563–2.926) and D4 (2.683–3.263), respectively. D2 has a positive correlation with moisture content, while D4 has a positive correlation with Ro and fixed carbon and a negative correlation with the volatile content. Both D2 and D4 have a weaker association with the ash yield and no apparent relationship with coal macerals, indicating that coal-forming materials and environments have little influence on the pore structure fractal characteristics. D2 has a strongly correlation with the BET surface area (R2=0.9026) and the average pore diameter (R2=0.9841), again proving that D2 can be used to characterize the pore structure fractal dimension of adsorbed pores. D2 shows a negative correlation with the Langmuir volume (VL), but no apparent relationship with the Langmuir pressure (PL), indicating that the pore structure of absorbed pores has little effect on methane desorption during the process of CBM exploitation. D4 has weak positive correlation with permeability. Overall, fractal analysis is beneficial for better understanding the pore structure, methane adsorbability and seepage ability of low-rank coal.

Investigation of Methane Desorption and Its Effect on the Gas Production Process from Shale: Experimental and Mathematical Study

A number of potential gas reserves are present in shale reservoirs around the world. The gas production process is more complex in shale reservoirs than in conventional reservoirs, mainly because of the ultralow permeability of the matrix, complex pore structure, and organic components that cause desorption. Long-term gas production comes from both free gas expansion and adsorbed gas desorption. In addition to the estimation of the gas content reserve in a reservoir, an accurate description of the effect of adsorbed gas on the dynamic gas production process is meaningful for predicting gas production from shale. Experimental and mathematical efforts have been undertaken to obtain an accurate description of the gas production process. This paper investigates desorption and diffusion, which are two of the key mechanisms in the shale matrix during gas production. The experimental results suggest that the gas production process from shale can be divided into two stages: free gas expansion from inorganic micro...

The Ono–Kondo model and an experimental study on supercritical adsorption of shale gas: A case study on Longmaxi shale in southeastern Chongqing, China

Adsorbed gas, the presence of which is a significant difference between the shale gas and conventional gases, has attracted considerable attention, particularly in China. A series of shale gas adsorption isotherms were measured at 30 °C and at pressures up to 10.94 MPa for the lower Silurian marine shale of the Longmaxi Formation collected in southeastern Chongqing, China. The maximum adsorbed gas content was 0.72–3.89 m3/t. Using measurements of the total organic carbon (TOC), thermal maturity, X-ray diffraction and low-pressure nitrogen adsorption, the basic characteristics of the shale reservoir were analyzed. The Ono–Kondo model was used to fit the measured methane adsorption isotherms with correlation coefficients as high as 0.9896–0.9976. The model characterized the filling adsorption features of nanopores under supercritical conditions. Monolayer saturated adsorption is generally less than the maximum adsorption, suggesting that as pressure increases, methane adsorption tends to become a multilayer adsorption. Among the geological parameters, TOC displayed a strong positive correlation with shale gas adsorption capacity. No obvious relation between the shale gas adsorption capacity and the clay was observed, indicating that organic matter has more significant contribution to shale gas adsorption than clay. The adsorption capacity significantly increased linearly with increasing total surface area, suggesting significant effects of pore structure on the shale gas storage. On the basis of the pressure sensitivity of adsorption rate, the adsorption process was divided into three stages: (1) an initial low-pressure stage, (2) an intermediate-pressure stage, and (3) a high-pressure stage. The third stage displayed methane desorption at high pressure. The similarities and differences of the Langmuir model and the Ono–Kondo model were assessed. An evaluation of which model is more accurate is difficult because both models can show good fits to experimental data. However, considering the methane adsorption mechanism, the Ono–Kondo model appears to be more reliable in describing the process of methane adsorption in shale because it predicts a more reasonable supercritical adsorption and can reflect the adsorption transformation from monolayer to multiple layers.

Experimental study on sonic vibrating effects of cavitation water jets and its promotion effects on coalbed methane desorption

To enhance the desorption of coalbed methane and increase the efficiency of gas extraction, a technique method based on the sonic vibrating effects of cavitation water jets to promote methane desorption is proposed. With proper devices, we conduct an experiment of using sonic vibrating effects of cavitation water jets to accelerate methane desorption. This is based on experiment tests on the mechanical vibration and thermal effects caused by the sonic vibrating effects. During the collapse phase of cavitation bubbles, the strong sonic vibrating effects may cause intense mechanical vibration and thermal effects. The vibration acceleration root-mean-square value presents an approximate positive linear correlation with the total volume of methane desorption. The mechanical vibration effect plays a dominant role in promoting the methane desorption, while the facilitation of thermal effect is relatively weaker. There is an obvious accelerating impact of sonic vibrating effects on coalbed methane desorption and the ultimate methane desorption volume increases by from 13.4 to 42.1% respectively, while desorption time shortens by between 12.5 and 21.5%. The study results bear an important significance on revealing the mechanism of promoting the methane desorption by sonic vibrating effects and field application of the technique method to CBM development.

Glass Transition, Crystallization, Melting, and Decomposition of Nanoconfined Propane Films at Cryogenic Temperatures

This study investigated translational diffusion of propane in thin films at cryogenic temperatures to elucidate crystallization and premelting of nanoconfined systems. The propane crystallizes on a Ni(111) substrate at around 48 K, but mobile molecules evolve on the surface immediately after crystallization, as revealed from their permeation through pores and gradual change in film morphology up to 80 K. The liquidlike behavior is attributable to surface premelting of crystallites. The crystallites become larger via surface diffusion, but the premelting layer thickness does not change over a wide temperature range. The crystal cores start to melt at 5 K below the bulk melting point, at which temperature the melting layer thickness increases dramatically. This behavior is consistent with the surface melting of macroscopic systems. Liquidlike propane molecules decompose at the interface of a deoxygenated V substrate during crystallization and premelting, as revealed from methane desorption via C–C bond trun...

Learnings from a failed nitrogen enhanced coalbed methane pilot: Piceance Basin, Colorado

A nitrogen flood, ECBM micro pilot was carried out in a deep, low permeability Cameo coal zone of the Mesavede Group in the Piceance Basin. The pilot project entailed the injection of about 28mmcf (7.9E5m3) of nitrogen over a period of 15days at pressures about 650psig (4482kPa) above the initial reservoir pressure, followed by a soak period of 15days, and subsequently 11days of flow back. The nitrogen flood was a failure inasmuch as there was no pressure change nor nitrogen or methane breakthrough in three closely adjacent monitoring wells, which were considered necessary to meet the metrics required for a field scale economic ECBM project.The results of the pilot test, in conjunction with subsequent laboratory field simulation tests and numerical modeling, are consistent in that they show injection of nitrogen, of necessity above reservoir pressure, neither displaced methane nor promoted methane desorption from the low permeability Cameo coal. The results suggest the injection of nitrogen above reservoir pressure increases the total adsorbed gas resulting in swelling of the coal, which increases the effective stress and hence decreases permeability, the reverse of what is intended. The field, laboratory, and numerical results indicate that for a nitrogen ECBM flood to initiate, in coal such as studied here, the in situ permeability must be high enough that nitrogen can displace, and thus reduce the partial pressure for methane. The results thus indicate that ECBM production by nitrogen flooding will only work in coals where the pre-existing permeability is high enough that conventional coalbed methane production is possible or has already been carried out.Results of our studies provide learnings relevant to carbon dioxide sequestration and ECBM for coals of similar properties to those of this study. An initial high permeability is critical, particularly for carbon dioxide injection, due to its higher volumetric strain coefficient and greater adsorption affinity than methane or nitrogen. Such high in situ permeability exists mainly in shallow coals, which also have the potential of being exploited in the future as a resource and hence may not be viable sites for long term carbon dioxide sequestration.

Coalbed methane adsorption and desorption characteristics related to coal particle size**Project supported by the National Basic Research Program of China (Grant No. 2011CB201202).

Effects of particle size on CH4 and CO2 adsorption and desorption characteristics of coals are investigated at 308 K and pressures up to 5.0 MPa. The gas adsorption and desorption isotherms of coals with particle sizes ranging from 250 μm to 840 μm are measured via the volumetric method, and the Langmuir model is used to analyse the experimental results. Coal particle size is found to have an obvious effect on the coal pore structure. With the decrease of coal particle size in the process of grinding, the pore accessibility of the coal, including the specific surface area and pore volume, increases. Hence, coal with smaller particle size has higher specific surface area and higher pore volume. The ability of adsorption was highly related to the pore structure of coal, and coal particle size has a significant influence on coal adsorption/desorption characteristics, including adsorption capacity and desorption hysteresis for CH4 and CO2, i.e., coal with a smaller particle size achieves higher adsorption capacity, while the sample with a larger particle size has lower adsorption capacity. Further, coal with larger particle size is also found to have relatively large desorption hysteresis. In addition, dynamic adsorption performances of the samples are carried out at 298 K and at pressures of 0.1 MPa and 0.5 MPa, respectively, and the results indicate that with the increase of particle size, the difference between CO2 and CH4 adsorption capacities of the samples decreases.

Mechanisms for homogeneous and heterogeneous formation of methane during the carbon–hydrogen reaction over zigzag edge sites

Methane is the main product in the reaction between molecular hydrogen and carbonaceous materials such as char, graphene and graphite. Although, pathways for the formation of methane in the carbon-hydrogen reaction have been proposed attending to experimental and molecular modeling results, there is not compelling evidence of the elementary character of the steps in such pathways. In this work we propose possible mechanisms with details at molecular level that account for the formation of methane at the zigzag edge through elementary steps using molecular modeling within the framework of the density functional theory. These mechanisms involve saturation of reactive sites, hydrogenation of the edge, ring opening and desorption of methyl groups or direct desorption of methane. Thermodynamic and kinetic details for all steps were explored over temperature and pressure ranges going from 298 K to 1500 K (at 0.1 MPa) and 0.1 MPa–10 MPa (at 1100 K), respectively. The proposed mechanisms show a remarkable qualitative agreement between predicted behavior of overall state functions (ΔHtot, ΔStot, and ΔGtot) and the equilibrium constant for the formation of methane and the observed experimental behavior of these thermodynamic quantities for standard formation of methane from 298 K to 1500 K.

Features of the kinetics of methane desorption from coal to a storage vessel

Features of the kinetics of methane desorption from coal to a storage vessel

Impact of fracturing fluid on multi-scale mass transport in coalbed methane reservoirs

The effect of fracturing fluid on multi-scale mass transport, including methane desorption, diffusion and percolation, was investigated on an anthracite coal from the Qinshui Basin. Methane sorption and diffusion characteristics were measured using the volumetric method. The Langmuir equation was used to fit the sorption isotherm data and unipore model to estimate the effective diffusion coefficient (De). The impairment of gas permeability, characterized by the residual resistance factor (Frr,g), was determined using the pulse-decay method. In addition, changes in pore structure and surface properties were also analyzed by SEM/EDX, low-temperature N2 adsorption and XPS. The results show that the methane adsorption capacity was reduced by 10.5% after fracturing fluid treatment. The Langmuir volume (VL) decreased while the Langmuir pressure (PL) increased, which is beneficial for gas desorption. The effective diffusion coefficient (De) exhibited a negative correlation with pressure and decreased by 23.0% to 37.6%. The gas permeability was significantly diminished and Frr,g for a macro-fractured sample was much greater than that for a micro-fractured sample. Furthermore, due to the adsorption of fracturing fluid on pore/fracture walls, the mass transport channels were narrowed and hydrophilia was enhanced. This possibly explains the reduction of gas adsorption capacity and mass transport rate in coal.

An anomalous subdiffusion model with fractional derivatives for methane desorption in heterogeneous coal matrix

Methane desorption in coal matrix is one of the fundamental gas transport processes during coalbed methane extraction, the mechanism of which is commonly described by Fickian diffusion theory. Here, an anomalous subdiffusion model with fractional derivatives is developed to explore the methane desorption in coal matrix with a highly heterogeneous pore structure. Numerical simulations reproduce the volume fraction of gas desorbed over the entire timescale of experimental desorption. It is suggested that the diffusion of methane in heterogeneous coal matrix may obey the anomalous time and space subdiffusion, rather than Fickian second law. The physical reason is perhaps due to the basic topological complexity inherent to porous coal matrix and the strong adsorption effect of coal on methane molecules.

Desorption area and pressure-drop region of wells in a homogeneous coalbed

The coalbed methane (CBM) desorption area is highly important in the placement of wells to produce an adequate working system. This paper develops a homogeneous seepage model of CBM that incorporates desorption and uses a finite-element method to obtain the pressure field in complex boundary cases influenced by adjacent wells. The pressure field is presented in a 2D and pseudo-3D form that visually demonstrates the shape of the pressure profile and the pressure expansion. A method of combined numerical computation and contour drawing technology is used to determine the CBM desorption area and pressure drop region. By analyzing the main factors that affect the CBM desorption region, we demonstrate that a higher value of critical desorption pressure yields a larger desorption area of the seam. The effect of the permeability is different from the value of the critical desorption. This effect is determined by the critical desorption pressure level and the intersection of pressure profiles with different permeabilities. Permeability anisotropy leads to a desorption area with an elliptical shape. We also demonstrate that a greater flux of methane will result in a greater desorption region, and the effects of the distance between wells and the desorption area are closely related to the permeability. The developed model is applied in a field case to predict the desorption area.

Methane adsorption-induced coal swelling measured with an optical method

In order to quantify the effect of matrix shrinkage on reservoir permeability during coalbed methane production, coal samples from Huozhou, Changzhi and Jincheng areas in Shanxi province (classified as high-volatile bituminous coal, low-volatile bituminous coal and anthracite, respectively) were collected, and adsorption-induced coal swelling in methane were determined by an optical method at 40°C and pressure up to 12MPa. All three coals showed similar behavior-that swelling increased as a function of pressure up to about 10MPa but thereafter no further increase in swelling was observed. Swelling in the direction perpendicular to the bedding plane is greater than that parallel to the bedding plane, and the differences are about 7.77–8.33%. The maximum volumetric swelling ranges from 2.73% to 3.21%-increasing with increasing coal rank. The swelling data can be described by a modified DR model. In addition, swelling increases with the amount of adsorption. However, the increase shows a relatively slower stage followed by a relatively faster stage instead of a linear increase. Based on the assumption that sorption-induced swelling/shrinkage of coal in methane is reversible, the permeability increases induced by coal shrinkage during methane desorption was analyzed, and the results indicate that the permeability change is larger for higher rank coal in the same unit of pressure depletion.

CO2 storage by sorption on organic matter and clay in gas shale

In the work described in this paper, we developed simulations of methane production and supercritical carbon dioxide injection that consider competitive sorption of methane (CH4) and carbon dioxide (CO2) on both organic matter and the clay mineral montmorillonite. We used the results of these simulations to assess the potential for storage of CO2 in a hydraulically fractured shale gas reservoir and for enhanced recovery of CH4. Assuming equal volume fractions of organic matter and montmorillonite, amounts of CO2 adsorbed on both materials were comparable, while methane desorption from clays was greater than desorption from organic material. CO2 injection simultaneous to CH4 production in two separate wells enhanced the contribution of methane desorption from 3535 to 6401metrictons, while storing 82metrickilotons of CO2.

Characterization of Nanosilica of Tapioca Peel as Adsorbent for Biomethane Storage System

Biomethane is an alternative and renewable source that occurred naturally which produced from the anaerobic digestion of organic matter. It can be used as the electricity power generation, water heating and also vehicle fuel. In this study, the characteristics of the nanosilica of the tapioca peel as an adsorbent on the structural and physical properties to store the biomethane were investigated. To enhance the adsorption and desorption performance as well as the structural and physical properties, the nanosilica was modified with the metal oxides. The metal oxides that have been used to modify the nanosilica adsorbent are zinc (II) oxide (ZnO) and nickel (II) oxide (NiO). Both of the modified and unmodified nanosilica structural properties were characterized by using X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM). While, the physical properties of both of the modified and unmodified nanosilica were characterized by using Brunauer, Emmet, Teller (BET) surface area measurement. The effects of both types of metal oxides with different concentration were investigated. Based on the results obtained, the structural and physical characteristics of the nanosilica were affected by the different metal oxides loading. It have been identified that 1% ZnO modified nanosilica has highest BET surface area (8.32 m2/g) with pore volume (19.23 cc/g) and pore size (82.8 nm). Thus, it concluded that 1% ZnO modified nanosilica improved the structural and physical structure. Hence, it enhances the capacity of methane adsorption and desorption prior to storage system.

Effect of Water Invasion on Outburst Predictive Index of Low Rank Coals in Dalong Mine.

To improve the coal permeability and outburst prevention, coal seam water injection and a series of outburst prevention measures were tested in outburst coal mines. These methods have become important technologies used for coal and gas outburst prevention and control by increasing the external moisture of coal or decreasing the stress of coal seam and changing the coal pore structure and gas desorption speed. In addition, techniques have had a significant impact on the gas extraction and outburst prevention indicators of coal seams. Globally, low rank coals reservoirs account for nearly half of hidden coal reserves and the most obvious feature of low rank coal is the high natural moisture content. Moisture will restrain the gas desorption and will affect the gas extraction and accuracy of the outburst prediction of coals. To study the influence of injected water on methane desorption dynamic characteristics and the outburst predictive index of coal, coal samples were collected from the Dalong Mine. The methane adsorption/desorption test was conducted on coal samples under conditions of different injected water contents. Selective analysis assessed the variations of the gas desorption quantities and the outburst prediction index (coal cutting desorption index). Adsorption tests indicated that the Langmuir volume of the Dalong coal sample is ~40.26 m3/t, indicating a strong gas adsorption ability. With the increase of injected water content, the gas desorption amount of the coal samples decreased under the same pressure and temperature. Higher moisture content lowered the accumulation desorption quantity after 120 minutes. The gas desorption volumes and moisture content conformed to a logarithmic relationship. After moisture correction, we obtained the long-flame coal outburst prediction (cutting desorption) index critical value. This value can provide a theoretical basis for outburst prediction and prevention of low rank coal mines and similar occurrence conditions of coal seams.

Damage mechanism and protection measures of a coalbed methane reservoir in the Zhengzhuang block

The Zhengzhuang block is an important development area in Qinshui basin in Shanxi Province, China. In this block, the amount of gas produced in many wells is not consistent with that predicted according to data concerning reservoir properties, even after fracturing (i.e., with clean fracturing fluid) or the implementation of horizontal boreholes through the reservoir. To investigate the damage mechanism, mineral composition and microstructures were analyzed using X-ray diffraction, scanning electron microscopy and thin section analysis; pore parameters were determined by a mercury intrusion test; hydration properties were tested by a dispersion and expansion experiment; the contact angle of water on reservoir cores was measured to analyze the wettability; and the sensitivities of NO. 3 coal cores were analyzed according to core flow experiments and an isothermal adsorption test. Based on the test results, the factors causing damage to the coalbed methane (CBM) reservoir in the NO. 3 coal seam included serious water blocking and stress sensitivity, followed by velocity sensitivity, water sensitivity, alkali sensitivity and acid sensitivity. To eliminate water blocking, an agent to adjust core wettability was chosen. Moreover, a new cheap inhibitor was provided to reduce core water sensitivity. Using the selected wettability adjustment agent, the inhibitor and other necessary additives, drilling fluid and fracturing liquid systems were optimized, causing considerably less damage to CBM reservoir cores, both in the wet and dry states, according to the results of core permeability tests. Compared with surface water and drilling mud applied during drilling in the gas field of the Zhengzhuang block, the optimized drilling fluid and fracturing liquid can promote methane desorption by reducing the Langmuir volume and increasing the Langmuir pressure of coal, thereby increasing gas production and recoverability of the CBM reservoir.

Laboratory measurements of methane desorption on coal during acoustic stimulation

An apparatus considering the impacts of acoustic waves (mechanical vibration effect, thermal effect, and the cavitation effect) was designed to study the characteristics of gas adsorption and desorption on coals. Experiments of methane desorption on coals were performed under the effects of different acoustic frequencies and different acoustic intensities. The results showed that acoustic wave has promoted desorption of methane on coals. It was found that the initial desorption rate is relatively high, and then desorption rate decreases slowly with time, and finally achieves equilibrium. The desorption amount of methane on coals under the effect of acoustic waves is higher than that obtained without acoustic waves, and we found that desorption amount of methane on coals increases as acoustic intensities increase. It was also found that desorption rate of methane on coals is promoted under the effect of acoustic waves. Since the existing desorption models cannot describe the desorption characteristics of methane on coals under the effect of the acoustic intensity, a correction term was introduced into the existing models in this study, and thus a new model that is able to describe methane desorption under the effect of acoustic waves was established. The promotion mechanism of methane desorption on coals by the acoustic waves was also studied, it was found that the thermal effect of acoustic waves on methane desorption can be clearly seen.

Computational Investigation of Electronic and Steric Effects in Surface Reactions of Metalorganic Precursors on Functionalized Silicon Surfaces

Steric and electronic effects play a profound role in determining the mechanisms of surface reactions. In the case of reactions of metalorganic precursors on solid prefunctionalized surfaces, the contribution of these effects has to be considered both for the incoming metalorganic precursor molecule and for the functionalized surface itself. This study uses density functional theory calculations with simple cluster models to investigate the technologically important reactions of tetrakis(dimethylamido)titanium (TDMAT) and trimethylaluminum (TMA) with silicon surfaces functionalized with preadsorbed amines. This approach provides an opportunity to compare the contribution of electronic effects in the process of transamination for TDMAT and in the process of aluminum deposition followed by methane desorption for TMA. Bulky dimethylamido substituents of TDMAT are shown to suppress the electronic effects of the surface-bound amines unless the very open surface-bound structures of −NH2 and −NHF are compared. A...