Methane Desorption Research Articles

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.

The theoretical basis of model building for coal reservoir permeability: A review and improvement

The dynamic permeability of coal reservoirs is more complicated than that of conventional reservoirs because of the natural cleat system and matrix shrinkage induced by methane desorption. Many permeability models have been built, but each model has its focus, and the theoretical basis used by them vary, which makes it difficult to compare different models. In this paper, the theoretical basis (basic equations and key relations) of widely cited models was summarized and strictly analyzed. Three limitations were found: the double effect of matrix shrinkage on permeability was not been realized, the concept of effective stress was not clear, and a reliable fracture closure equation was lacking to describe the mechanical response of cleats. Corresponding improvements have been made. Firstly, a new porosity-effective stress relation is obtained without introducing new parameters, which can describe the double effect of matrix shrinkage. Secondly, expressions of three effective stresses considering matrix shrinkage are obtained: Biot effective stress controls the bulk volume strain, pore effective stress controls the pore volume strain, and porosity effective stress controls porosity change. Thirdly, an explicit fracture closure equation is introduced to obtain the analytical permeability models considering the mechanical properties of cleats. Finally, based on the above improvements, a new permeability model system is obtained. Compared with previous models by theoretical analysis, the new models are more comprehensive in considering matrix shrinkage, more accurate in using the effective stresses, and include analytical models based on the mechanical property of cleats.

Thermo-Hydro-Mechanical Coupling Numerical Simulation on Mechanical Heterogeneity of Coal Rock

Coal rock is a porous medium composed of organic matter and inorganic minerals, and it is very complex and highly heterogeneous. Coal bed methane (CBM) production is a thermo-hydro-mechanical (THM) coupling process in heterogeneous coal rock. THM coupling numerical simulation on the coal rock by considering the effect of mechanical heterogeneity is rarely reported. We use Weibull’s probability density distribution function to characterize the heterogeneity in elastic modulus of the coal rock, establish a THM coupling 3D finite element model of the coal rock by considering the variation in pore pressure caused by methane desorption, the linear thermal expansion effect, and coal rock skeleton shrinkage and deformation, and analyze variation in permeability, porosity, stress, temperature, and pore pressure within the coal rock representative elementary volume (REV) of variable mechanical heterogeneity with the cross-coupling correlation between permeability and porosity, and thermal field, stress field, and pressure field. The results show that the evolution of porosity and permeability in the coal rock is a THM coupling process related to mechanical heterogeneity, thermal expansion effect, pore pressure change caused by CBM desorption, and stressed deformation in the coal rock skeleton. The permeability and porosity fluctuate within the heterogeneous coal rock. The permeability and porosity fluctuate more frequently in the coal rock with stronger mechanical heterogeneity. The mechanical heterogeneity promotes local stress concentration. The time for variation in the stress through the whole the coal rock REV and the value of the first principal stress increase when the coal rock heterogeneity is enhanced. Under the THM coupling effect, the strong heterogeneity of the coal rock causes fluctuation in the thermal field. The evolution of coal porosity and permeability is a THM coupling process. This study provides theoretical guidance for CBM exploitation.

Mechanism of Methane Adsorption/Desorption in Low-Rank Vitrain and Durain Coal Affected by Pore Structure and Wettability: A Case Study in Dafosi Area, South Ordos Basin, China

Water content and water–coal interface wettability are always the difficult issues of coalbed methane adsorption/desorption. In order to study the effects of the pore structure and wettability of different macro coal components on methane adsorption and desorption, we compared and analyzed the wettability difference between vitrain and durain, and revealed the influence of wettability on methane adsorption and desorption through a pore structure analysis, wettability measurements, an adsorption–desorption experiment and adsorption heat calculations under different conditions, taking the No. 4 coal in Dafosi Coal Mine of the Huanglong coalfield as the research object. The results show that both vitrain and durain are relatively hydrophilic substances. However, vitrain has a low ash content, high volatility, and less oxygen, and the pores are mainly semi-closed pores compared with dark coal. Vitrain also has poor connectivity, poor sorting, a small pore diameter, and a coarser surface, resulting in poor surface wettability. The large specific surface area (SSA) and relatively poor wettability of vitrain leads to more adsorption sites in methane, which makes the adsorption capacity of vitrain greater than that of durain, but the good pore connectivity of durain causes the strong desorption capacity of durain. The isosteric adsorption heat of the adsorption process is greater than that of the desorption process, indicating that there is a desorption hysteresis phenomenon which is essentially due to the lack of energy in desorption. Surfactants change the wettability of the coal surface, and different surfactants have different effects on methane adsorption and desorption. Relatively speaking, the methane desorption of coal samples treated with G502 and 6501 are better. The research results provide scientific reference for the study of gas–water transport in the desorption process of low-rank CBM, and provide evidence for the methane desorption model of vitrain and durain.

Interference mechanism in coalbed methane wells and impacts on infill adjustment for existing well patterns

Inter-well interference, a superimposed effect of pressure propagation from adjacent wells, can enhance the dynamics of methane desorption in pores and gas transport in fractures through energy migration. To better understand the variation pattern of seepage efficiency, the inter-well interference mechanism of different types of reservoirs and productivity changes after infilling coalbed methane wells were investigated. The results showed that the average productivity of old wells increased by 627 m3/d after infilling a horizontal well in the high-permeability reservoirs without surrounding rock water supply (HP-WW); however, the newly infilled horizontal well produced gas at 4996 m3/d. The infill well in HP-WW reservoir resulted in 11％-39％permeability increment compared with initial permeability (the average permeability changes from 1.58 to 2.18 mD). While, much higher permeability increment was observed (varies from 29％-50％) in relative low permeability coalbed formation due to infill well. After the formation of interference, increased confining pressure increases effective stress, which is smaller than the positive effect formed by the fracture expansion and the increase in the effective diffusion area. Additionally, well interference promotes coupled superposition of the pressure drop funnel, which effectively suppresses the influence induced by velocity sensitivity, water sensitivity, and water lock, resulting in an increased pressure difference between the reservoir and the wellbore. This enhances the dynamics of methane desorption from the pore surface and gas migration from the fracture. For gas diffusion, the mean free path of gas molecules decreases with well interference, implying that the main diffusion resistance changes from collisions between gas molecules and the pore wall to collisions among gas molecules. Therefore, the findings of this study can help for better understanding of the response mechanism of inter-well interference to efficient CBM production.

Experimental study on improving coalbed methane extraction by chemical treatment using acetic acid or ammonium persulfate

AbstractAd‐/desorption and diffusion processes are the key factors controlling methane production from coal. The experiments used samples from methane‐producing coal seams with different contents of carbonate mineral and different ranks. Acid treatment using 1.0 mol/L acetic acid (CH3COOH) and oxidant treatment using 1.0 mol/L ammonium persulfate ((NH4)2S2O8) were conducted on these coal samples to observe the changes in surface functional groups that act as primary sorption sites and pore structure that determines diffusivity by Fourier transform infrared spectrometer, in situ scanning electron microscopy (SEM) imaging and energy dispersive spectroscopy. The results showed that the acidizing‐related mass loss of coal samples is in the range of 3.78%–7.57% due to the complete dissolution of pore‐ and fracture‐filling carbonate minerals. For the coal samples after oxidizing treatment, dissolution evidence can be observed in both carbonate minerals and organic matter, with a mass loss ranging from 2.01% to 3.0%. Acidizing or oxidizing induced dissolution can destroy aliphatic functional groups and the cross‐linked structure of coal, resulting in a decrease in methane adsorption capacity that is beneficial to methane desorption. More opened pores and interconnected fractures can be observed in SEM images due to the dissolution of carbonate minerals, suggesting an alteration of methane diffusion pathways in the coal matrix. Although only some of the carbonate minerals were dissolved following oxidant treatment, coal organic matter is partially oxidized and generates some dissolution pores, which provides more methane diffusion pathways in the coal matrix. Therefore, all the treated coal samples showed a reduction in methane adsorption capacity and an enhancement of desorption capacity and diffusivity. This result suggests that chemical treatment in coal seams using acetic acid or oxidant has the potential to improve coalbed methane extraction.

Desorption and diffusion characteristics of methane in the non-ventilation working face

Based on the rapid development of intelligent unmanned mining technology in coal mines, a new concept of non-ventilation working face is put forward. In the absence of ventilation, it is more possible to extract high purity methane and eliminate coal mine accidents. There are few studies on the desorption and diffusion characteristics of methane under constant positive pressure (higher than atmospheric pressure) in the non-ventilation working face. In this study, a set of self-designed gas positive pressure desorption equipment was used to carry out desorption experiments under various positive environmental pressures. The diffusion coefficient of methane in coal was calculated by using the unipore diffusion model. The results indicate that the extended Langmuir EXT1 model can well describe the variation of methane desorption capacity with time under different positive pressures. Under the same temperature and equilibrium pressure, the limit desorption capacity and desorption rate of methane in coal decrease with the increase of external positive pressure. With the increase of temperature and equilibrium pressure, the negative effect of positive pressure is weakened. At the same temperature and equilibrium pressure, the diffusion coefficient of methane in coal decreases with the increase of positive pressure. The higher equilibrium pressure increases the methane concentration in coal matrix and weakens the influence of positive pressure on the concentration difference, which slows down the decreasing rate of diffusion coefficient. On the contrary, the increase in temperature reduces the methane concentration in coal matrix and accelerates the decreasing rate of diffusion coefficient. These results provide theoretical guidance for the realization of the non-ventilation working face.

Effect of long-term operations on the performance of hollow fiber membrane contactor (HFMC) in recovering dissolved methane from anaerobic effluent

Various studies provide information about the high potential of using hollow fiber membrane contactors (HFMCs) for the recovery of dissolved methane from anaerobically treated wastewater effluent and the effects of different operating conditions on their performance. However, majority of those studies evaluated HFMCs at bench scale under favorable conditions, i.e. clean water as feed under short-term operations. This study evaluated the performance of porous HFMC and dense HFMC (in terms of dissolved methane removal efficiency and methane desorption flux) subjected to anaerobic feed during long-term operation of one month. The study will provide better understanding of the performance of HFMCs with conditions expected at large-scale wastewater treatment systems. From the results, the decrease in the performance of HFMCs and the increase in the mass transfer resistance per week under varying feed flux were determined. These relationships were utilized in a numerical model to incorporate the effect of long-term operation to evaluate the performance of upscaled HFMCs. The fit of the model with the experimental data with one month of operation was evaluated and the relative errors were 11.9 % and 15.3 % for porous HFMC and dense HFMC, respectively. Moreover, results showed that dense HFMC will provide better performance than porous HFMC if it were to be operated longer than two weeks before cleaning. The net energy for porous HFMC and dense HFMC were optimized to be 0.07 and 0.02 kWh·d−1, respectively. Although these results are specific to the operations and conditions used for the HFMCs in this study, the methodology established for incorporating the effect of long-term operation will be highly relevant in evaluating the performance of HFMCs in large-scale wastewater treatment applications. This will contribute to the improved recovery of dissolved methane to reduce the greenhouse gas emissions in the atmosphere and to provide additional source of clean and sustainable energy.

Pore Structure Characteristics and Adsorption and Desorption Capacity of Coal Rock after Exposure to Clean Fracturing Fluid.

In the hydraulic fracturing process, fracturing fluid contacts coal rock and physical and chemical reactions occur, which inevitably damage the pore structure of the coal rock and affect the adsorption and desorption capacity of the coal rock. In this paper, a low-temperature N2 adsorption method and scanning electron microscopy (SEM) were used to characterize coal samples. Using gas adsorption/desorption tests, high-, medium-, and low-rank coal samples before and after the clean fracturing fluid treatment were systematically studied. According to the relationship between coal pore structure parameters and gas adsorption/desorption characteristics, a correlation between the microscopic pore structure and the macroscopic gas adsorption/desorption characteristics of coal was obtained. The results show that the number of closed pores in high-, medium-, and low-rank coal samples increased after the clean fracturing fluid treatment. The micropore volume increased by 0.0009, 0.00143, and 0.0035 mL/g, respectively, and the specific surface area increased by 4.87, 9.06, and 57.60%. The fractal dimension also increased compared with that of raw coal. SEM analysis indicated that the influence degree of clean fracturing fluid treatment on the pore structure of different-rank coal samples was Gengcun low-rank coal > Pingba middle-rank coal > Jiulishan high-rank coal. The experimental results of methane adsorption and desorption showed that the adsorption capacity of the coal samples after clean fracturing fluid treatment was enhanced, which is related to increases in the micropore proportion, micropore volume, and specific surface area of the coal. The desorption capacity of the coal samples was also enhanced. The desorption rate of medium- and high-rank coal samples increased after the clean fracturing fluid treatment but that of low-rank coal samples decreased. The main reason is the increase in the number of micropores in low-rank coal, which enhances the gas adsorption ability and makes gas desorption difficult. Therefore, clean fracturing fluid is suitable for medium- and high-grade metamorphic coalbed methane mines. These research results provide a theoretical basis for the application of clean fracturing fluid in different coalbed methane wells.

Co3+–O Bond Elongation Unlocks Co3O4 for Methane Activation under Ambient Conditions

The pursuit of low-temperature methane activation is a paramount challenge for heterogeneous catalysis because of the high stability of the C–H bonds (435 kJ mol–1). Very few catalysts fulfill this through either constructing complex interfaces or using special noble metal oxides. Bond length, which is highly temperature-sensitive, has long been ignored in catalyst studies. Here, we exploit a bond-length elongation strategy to unlock a nonprecious metal oxide for dissociating methane at normal temperature and pressure. Mesoporous bubblelike Co3O4 with elongated Co3+–O bonds, synthesized through a unique “melting–foaming–solidifying” route, is found to activate methane at room temperature to form COx species on the very surface revealed by temperature-programmed reaction spectroscopy experiments. A combination of experimental and theoretical methods suggests that the elongated Co3+–O bonds contribute to the greatly enhanced methane adsorption, in contrast to the weak adsorption of methane on conventional nonprecious metal oxides. Accordingly, the activation energy for the C–H bond cleavage is smaller than that for methane desorption, which finally leads to the low-temperature methane activation. The simultaneous enhancement in intrinsic activity and mass transfer endows mesoporous bubblelike Co3O4 with excellent catalytic activity for methane combustion, where the complete conversion temperature is much below that over the conventional Co3O4 nanocatalysts.

Comparative experimental study on the effects of water- and foam-based fracturing fluids on multiscale flow in coalbed methane

To quantitatively evaluate their influence on coalbed methane (CBM) flow, water- and foam-based fracturing fluids were prepared. The effects of these two fracturing fluids on the flow of methane in coal were compared and analyzed using isothermal adsorption, diffusion capacity, and seepage tests. The results showed that an increase in the concentration of the fracturing fluid can exacerbate damage to methane flow. After immersed with water-based gel, gas diffusivity in the coal sample dropped to less than one fifth of the original level. However, when immersed with foam-based fracturing fluid, the diffusion coefficient of coal samples exceeded 3 × 10−13 m2/s. The residual permeability of the coal samples measured at a high pressure was significantly greater than that measured at a low pressure. Compare with the foam, the gel will cause a more serious adverse impact on the permeability of coal samples. Foam fracturing fluids with low viscosity and higher volume fraction of the gas phase will cause lesser damage to methane adsorption, desorption, or percolation. These results can help in the development of a coal seam clean fracturing technology.

Effect of water on methane diffusion in coal under temperature and pressure: A LF-NMR experimental study on successive depressurization desorption

Coalbed methane production is a process of desorption, diffusion, and seepage with the successive decrease of reservoir pressure. However, desorption at atmospheric pressure has been mainly used to investigate the gas diffusion of water-bearing coal. The influence of confining pressure and gas pressure on methane diffusion is not considered in this case. So, the question is, how does the variation of the methane diffusion coefficient of water-bearing coal during desorption? How is it different from dry coal? What is the difference between the methane diffusion behavior of anthracite and bituminous coal? To address these problems, we select low-volatile anthracite in the south of Qinshui Basin and high-volatile bituminous coal in the south of Junggar Basin. The methane diffusion of water-bearing and dry coal during the successive depressurization desorption is compared by low field nuclear magnetic resonance. The influence mechanism of water on methane diffusion is explored from the pore structure, wettability, and external stress. The results show that the methane diffusion coefficient of water-bearing anthracite and bituminous coal increases with the decrease of gas pressure. The methane diffusion of water-bearing coal is affected by the combination of the increase of methane desorption volume (positive effect) and the increase of effective stress (negative effect). When the gas pressure decreases from 6 MPa to 2 MPa, the negative effect is dominant, and the effective diffusion coefficient of methane in coal is poor; When the gas pressure is less than 2 MPa, the positive effect is dominant and the effective diffusion coefficient increases significantly. The homogeneity of methane effective diffusion path of water-bearing anthracite is enhanced, resulting in higher methane desorption rate and effective diffusion coefficient than dry coal. The methane effective diffusion pore size of water-bearing bituminous coal decreases, resulting in the effective diffusion coefficient of methane less than that of dry coal. These results are of great significance to reveal the methane diffusion behavior of coalbed methane in the actual production.

Seasonality in Mars atmospheric methane driven by microseepage, barometric pumping, and adsorption

Measurements of atmospheric methane by the Curiosity rover's SAM-TLS instrument are providing evidence of seasonality with bimodal peaks in concentration. Given methane's short atmospheric lifetime relative to geological timescales, its presence implies a replenishing source, and the observed seasonality demands the proposition of a modulation mechanism. This paper focuses on the modulation mechanism. Our modeling study shows that barometric pumping driven by seasonal variation of atmospheric pressure, along with adsorption and desorption of methane in the shallow subsurface driven by temperature change, can explain the observed bimodal peaks in the seasonal variations of methane concentration. In the model, an active, continuous, steady-state deep source of methane is assumed, and carbon dioxide serves as the carrier gas for producing seasonal variation in the upper part of the sedimentary column for methane and other possible trace gaseous constituents. Our work also presents a comprehensive flow chart for modeling the microseepage of methane on Mars from first principles.

Dynamic characterization of multiphase methane during CO2-ECBM: An NMR relaxation method

Injecting CO2 into coal reservoirs is essential both for enhancing coalbed methane recovery (CO2-ECBM) and CO2 geological sequestration. However, due to the difficulty in simultaneously monitoring multiphase methane (adsorbed and free phases) by conventional testing methods, the real-time variations in different phases of methane throughout the whole process of CO2-ECBM still remains to be clarified. In this study, with the introduction of self-designed nuclear magnetic resonance (NMR) measurement, three subbituminous and anthracite coals collected from deep-well drilling were used to investigate the dynamic characteristics of multiphase methane in CO2-ECBM. The results show that the adsorbed methane desorption efficiency could be additionally improved by ∼ 14%–26% with the injection of CO2 after conventional reservoir depressurization. In the process of CO2-ECBM, three different CO2-CH4 displacement rates emerged: the rate rapidly decreased during the initial CO2 injection time period and then began to slowly decrease until reaching CO2-CH4 competitive-adsorption equilibrium. Comparison of the NMR transverse relaxation (T2) characteristics of CO2-ECBM after natural and in-situ methane adsorption suggests that a low concentration ratio of CH4/CO2 could significantly improve the methane recovery. The promising results from the CO2-CH4 displacement experiments demonstrate the great significance of the CO2-ECBM method in enhancing methane recovery and CO2 geological sequestration for coals.

Mathematical Model and Numerical Simulation of Coalbed Methane Migration Considering the Adsorption Expansion Effect

The influence of gas adsorption and desorption on the volumetric strain of coal was measured by a self-designed, fluid–solid coupling triaxial coal adsorption deformation experimental system. The experimental results show that coal deformation has a threshold value with an increase in gas content. Before the gas content reaches the threshold value, coal deformation is not obvious. When the gas content reaches the threshold value, the deformation will increase sharply. At the same time, coal volume strain changes with coal gas content in accordance with exponential law ε = ε0(eϒc-1). Based on the experimental results, considering the coupling effects of heat transfer, water seepage, coal and rock mass deformation, and coalbed methane desorption and seepage, a mathematical model of heat transfer–deformation–seepage coupling coalbed methane migration was established, and a numerical simulation study was carried out on the heat injection-enhanced coalbed methane mining project. The results show that (1) With continuous heat injection, the gas in the coal seam is rapidly desorbed, and the adsorbed gas content forms an elliptical funnel that extends from the extraction hole to the deep part of the coal body and takes the fracturing crack as the center to the upper and lower boundaries of the coal seam. At day 30, the adsorbed gas content in the whole drainage area has decreased to 0.1 m3/t within 2m from the fracture zone. (2) On the basis of considering the gas adsorption expansion effect, the strain of the coal body decreases from roof to floor. With the increase in the heat injection time, the strain value will also increase, and the strain increase will decrease. When the heat injection is 30 days, the maximum strain at the roof is 0.015. The research results have important guiding significance for predicting coal rock deformation and determining gas extraction efficiency in the process of heat injection-enhanced coalbed methane extraction.

Coalbed methane desorption characteristics controlled by coalification and its implication on gas co-production from multiple coal seams

Coalbed methane desorption characteristics controlled by coalification and its implication on gas co-production from multiple coal seams

Evaluation and analysis of methane adsorption capacity in deep‐buried coal seams

AbstractIn this work, the high‐pressure methane adsorption/desorption tests were conducted in four coal samples (from low‐rank bituminous coal to anthracite) under different temperature and pressure conditions to reveal the mechanism of desorption hysteresis effect in the deep‐buried coal seams. The experimental and fitting results show that the presence of free methane molecules in the adsorption phase results in an obvious difference between the measured methane adsorption amount with the actual adsorption capacity. The Langmuir, Langmuir–Freundlich (L–F) and Dubinin–Astakhov (D–A) models have their own advantages and disadvantages in fitting the experimental adsorption/desorption data. As residual adsorption capacity C fitted by the D–A model would be negative at high temperatures and lose the meaning of the constant, the Langmuir model is more suitable to describe methane desorption process. The residual adsorption capacity fitted by Langmuir model tended to decrease as the temperature increased until it is almost completely desorbed at 373 K. Meanwhile, because the adsorption sites with lower energy are gradually occupied by methane molecules in the high‐pressure stage, intermolecular forces increased and methane molecules are more easily desorbed. Therefore, the desorption hysteresis coefficient trends to increase exponentially with the decrease of pressure and temperature, which indicated that the original gas content of the coal seams may decrease with the increase of the burial depth, but the risk of coal and gas outburst accidents may increase. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Effects Of Matrix Swelling On Coal Permeability For Enhance Coalbed Methane (Ecbm) And Co2 Sequestration Assessment Part I: Laboratory Experiment

It has been reported that coal matrix swelling/shrinkage associated with CO2, adsorption/desorption are typically two to five times larger than that found for methane, yet there has been no direct measurements of this effect on permeability of coals to CO2. The feasibility of ECBM/CO2 sequestration technology depends very much on the magnitude of matrix swelling effect on permeability, especially in deep, low permeability coal seam reservoirs. The main objective of this research is to investigate the effects of coal matrix swelling induced by CO2 adsorption on the permeability of different coals which have been undergoing methane desorption under simulated reservoir conditions in the laboratory. Coal and reservoir properties which may impact upon this behaviour will be identified through extensive laboratory testing. This paper – first of two – presents the procedure for the laboratory tests as well as the findings. In the second part, a field permeability model for enhanced methane recovery and CO2 sequestration, incorporating the findings of the current laboratory tests, would be developed.

EFFECTS OF MATRIX SWELLING ON COAL PERMEABILITY FOR ENHANCE COALBED METHANE (ECBM) AND CO2 SEQUESTRATION ASSESSMENT PART I: LABORATORY EXPERIMENT

It has been reported that coal matrix swelling/shrinkage associated with CO2 , adsorption/desorption are typically two to five times larger than that found for methane, yet there has been no direct measurements of this effect on permeability of coals to CO2 . The feasibility of ECBM/CO2 sequestration technology depends very much on the magnitude of matrix swelling effect on permeability, especially in deep, low permeability coal seam reservoirs. The main objective of this research is to investigate the effects of coal matrix swelling induced by CO2 adsorption on the permeability of different coals which have been undergoing methane desorption under simulated reservoir conditions in the laboratory. Coal and reservoir properties which may impact upon this behaviour will be identified through extensive laboratory testing. This paper – first of two – presents the procedure for the laboratory tests as well as the findings. In the second part, a field permeability model for enhanced methane recovery and CO2 sequestration, incorporating the findings of the current laboratory tests, would be developed.

Effects Of Matrix Swelling On Coal Permeability For Enhance Coalbed Methane (Ecbm) And Co2 Sequestration Assessment Part Ii: Model Formulation And Field Application

In part II of this two-part paper series, a field permeability model for enhanced methane recovery and CO2 sequestration, incorporating the findings of the current laboratory tests presented in part I is presented. It has been reported that coal matrix swelling/shrinkage associated with CO2, adsorption/desorption are typically two to five times larger than that found for methane, yet there has been no direct measurements of this effect on permeability of coals to CO2. The feasibility of ECBM/CO2 sequestration technology depends very much on the magnitude of matrix swelling effect on permeability, especially in deep, low permeability coal seam reservoirs. The main objective of this research is to investigate and develop numerical models based on the the effects of coal matrix swelling induced by CO2 adsorption on the permeability of different coals which have been undergoing methane desorption under simulated reservoir conditions in the laboratory.