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1.
There is still no clear understanding of the specific interactions between coal and gas molecules. In this context sorption–desorption studies of methane and carbon dioxide, both in a single gas environment and gas mixtures, are of fundamental interest. This paper presents the results of unique simultaneous measurements of sorption kinetics, volumetric strain and acoustic emission (AE) on three tetragonal coal samples subjected to sorption of carbon dioxide and methane mixtures. The coal was a high volatile bituminous C coal taken from the Budryk mine in the Upper Silesia Basin, Poland. Three different gas mixtures were used in the sorption tests, with dominant CO2, with dominant CH4 and a 50/50 mixture.The experimental set-up was designed specially for this study. It consisted of three individual units working together: (i) a unit for gas sorption experiments using a volumetric method, (ii) an AE apparatus for detecting, recording and analysing AE, and (iii) a strain meter for measuring strains induced in the coal sample by gas sorption/desorption. All measurements were computer aided.The experiments indicated that the coal tested showed preferential sorption of CH4 at 2.6 MPa pressure and exhibited comparable affinities for CH4 and CO2 at higher pressures (4.0 MPa). The results of chromatographic analysis of the gas released on desorption suggested that the desorption of methane from the coal was favoured. The relationship between the volumetric strain and the amount of sorbed gas was found to be non-linear. These results were contrary to common opinions on the coal behaviour. Furthermore, it appeared that the swelling/shrinkage of coal was clearly influenced by the network of fractures. Besides, the AE and strain characteristics suggested common sources of sorption induced AE and strain.The present results may have implications for the sequestration of carbon dioxide in coal seams and enhanced coalbed methane recovery (ECBM).  相似文献   

2.
Sorption and desorption behaviour of methane, carbon dioxide, and mixtures of the two gases has been studied on a set of well-characterised coals from the Argonne Premium Coal Programme. The coal samples cover a maturity range from 0.25% to 1.68% vitrinite reflectance. The maceral compositions were dominated by vitrinite (85% to 91%). Inertinite contents ranged from 8% to 11% and liptinite contents around 1% with one exception (Illinois coal, 5%). All sorption experiments were performed on powdered (−100 mesh), dry coal samples.Single component sorption/desorption measurements were carried out at 22 °C up to final pressures around 51 bar (5.1 MPa) for CO2 (subcritical state) and 110 bar (11 MPa) for methane.The ratios of the final sorption capacities for pure CO2 and methane (in molar units) on the five coal samples vary between 1.15 and 3.16. The lowest ratio (1.15) was found for the North Dakota Beulah-Zap lignite (VRr=0.25%) and the highest ratios (2.7 and 3.16) were encountered for the low-rank coals (VRr 0.32% and 0.48%) while the ratio decreases to 1.6–1.7 for the highest rank coals in this series.Desorption isotherms for CH4 and CO2 were measured immediately after the corresponding sorption isotherms. They generally lie above the sorption isotherms. The degree of hysteresis, i.e. deviation of sorption and desorption isotherms, varies and shows no dependence on coal rank.Adsorption tests with CH4/CO2 mixtures were conducted to study the degree of preferential sorption of these two gases on coals of different rank. These experiments were performed on dry coals at 45 °C and pressures up to 180 bar (18 MPa). For the highest rank samples of this sequence preferential sorption behaviour was “as expected”, i.e. preferential adsorption of CO2 and preferential desorption of CH4 were observed. For the low rank samples, however, preferential adsorption of CH4 was found in the low pressure range and preferential desorption of CO2 over the entire pressure range.Follow-up tests for single gas CO2 sorption measurements consistently showed a significant increase in sorption capacity for re-runs on the same sample. This phenomenon could be due to extraction of volatile coal components by CO2 in the first experiment. Reproducibility tests with methane and CO2 using fresh sample material in each experiment did not show this effect.  相似文献   

3.
This paper presents reviews of studies on properties of coal pertinent to carbon dioxide (CO2) sequestration in coal with specific reference to Victorian brown coals. The coal basins in Victoria, Australia have been identified as one of the largest brown coal resources in the world and so far few studies have been conducted on CO2 sequestration in this particular type of coals. The feasibility of CO2 sequestration depends on three main factors: (1) coal mass properties (chemical, physical and microscopic properties), (2) seam permeability, and (3) gas sorption properties of the coal. Firstly, the coal mass properties of Victorian brown coal are presented, and then the general variations of the coal mass properties with rank, for all types of coal, are discussed. Subsequently, coal gas permeability and gas sorption are considered, and the physical factors which affect them are examined. In addition, existing models for coal gas permeability and gas sorption in coal are reviewed and the possibilities of further development of these models are discussed. According to the previous studies, coal mass properties and permeability and gas sorption characteristics of coals are different for different ranks: lignite to medium volatile bituminous coals and medium volatile bituminous to anthracite coals. This is important for the development of mathematical models for gas permeability and sorption behavior. Furthermore, the models have to take into account volume effect which can be significant under high pressure and temperature conditions. Also, the viscosity and density of supercritical CO2 close to the critical point can undergo large and rapid changes. To date, few studies have been conducted on CO2 sequestration in Victorian brown coal, and for all types of coal, very few studies have been conducted on CO2 sequestration under high pressure and temperature conditions.  相似文献   

4.
The sensitivity of coal permeability to the effective stress means that changes in stress as well as pore pressure within a coal seam lead to changes in permeability. In addition coal swells with gas adsorption and shrinks with desorption; these sorption strains impact on the coal stress state and thus the permeability. Therefore the consideration of gas migration in coal requires an appreciation of the coupled geomechanical behaviour. A number of approaches to representing coal permeability incorporate the geomechanical response and have found widespread use in reservoir simulation. However these approaches are based on two simplifying assumptions; uniaxial strain (i.e. zero strain in the horizontal plane) and constant vertical stress. This paper investigates the accuracy of these assumptions for reservoir simulation of enhanced coalbed methane through CO2 sequestration. A coupled simulation approach is used where the coalbed methane simulator SIMED II is coupled with the geomechanical model FLAC3D. This model is applied to three simulation case studies assembled from information presented in the literature. Two of these are for 100% CO2 injection, while the final example is where a flue gas (12.5% CO2 and 87.5% N2) is injected. It was found that the horizontal contrast in sorption strain within the coal seam caused by spatial differences in the total gas content leads to vertical stress variation. Thus the permeability calculated from the coupled simulation and that using an existing coal permeability model, the Shi–Durucan model, are significantly different; for the region in the vicinity of the production well the coupled permeability is greater than the Shi–Durucan model. In the vicinity of the injection well the permeability is less than that calculated using the Shi–Durucan model. This response is a function of the magnitude of the strain contrast within the seam and dissipates as these contrasts diminish.  相似文献   

5.
Supercritical gas sorption on moist coals   总被引：2，自引：1，他引：1  
The effect of moisture on the CO2 and CH4 sorption capacity of three bituminous coals from Australia and China was investigated at 55 °C and at pressures up to 20 MPa. A gravimetric apparatus was used to measure the gas adsorption isotherms of coal with moisture contents ranging from 0 to about 8%. A modified Dubinin–Radushkevich (DR) adsorption model was found to fit the experimental data under all conditions. Moisture adsorption isotherms of these coals were measured at 21 °C. The Guggenheim–Anderson–de Boer (GAB) model was capable of accurately representing the moisture isotherms over the full range of relative pressures.Moist coal had a significantly lower maximum sorption capacity for both CO2 and CH4 than dry coal. However, the extent to which the capacity was reduced was dependent upon the rank of the coal. Higher rank coals were less affected by the presence of moisture than low rank coals. All coals exhibited a certain moisture content beyond which further moisture did not affect the sorption capacity. This limiting moisture content was dependent on the rank of the coal and the sorbate gas and, for these coals, corresponded approximately to the equilibrium moisture content that would be attained by exposing the coal to about 40–80% relative humidity. The experimental results indicate that the loss of sorption capacity by the coal in the presence of water can be simply explained by volumetric displacement of the CO2 and CH4 by the water. Below the limiting moisture content, the CO2 sorption capacity reduced by about 7.3 kg t− 1 for each 1% increase in moisture. For CH4, sorption capacity was reduced by about 1.8 kg t− 1 for each 1% increase in moisture.The heat of sorption calculated from the DR model decreased slightly on addition of moisture. One explanation is that water is preferentially attracted to high energy adsorption sites (that have high energy by virtue of their electrostatic nature), expelling CO2 and CH4 molecules.  相似文献   

6.
A theoretical model for gas adsorption-induced coal swelling   总被引：6，自引：2，他引：6  
Swelling and shrinkage (volumetric change) of coal during adsorption and desorption of gas is a well-known phenomenon. For coalbed methane recovery and carbon sequestration in deep, unminable coal beds, adsorption-induced coal volumetric change may cause significant reservoir permeability change. In this work, a theoretical model is derived to describe adsorption-induced coal swelling at adsorption and strain equilibrium. This model applies an energy balance approach, which assumes that the surface energy change caused by adsorption is equal to the elastic energy change of the coal solid. The elastic modulus of the coal, gas adsorption isotherm, and other measurable parameters, including coal density and porosity, are required in this model. Results from the model agree well with experimental observations of swelling. It is shown that the model is able to describe the differences in swelling behaviour with respect to gas species and at very high gas pressures, where the coal swelling ratio reaches a maximum then decreases. Furthermore, this model can be used to describe mixed-gas adsorption induced-coal swelling, and can thus be applied to CO2-enhanced coalbed methane recovery.  相似文献   

7.
Laboratory experiments were conducted to investigate the adsorption kinetic behavior of pure and mixed gases (CO2, CH4, approximately equimolar CO2 + CH4 mixtures, and He) on a coal sample obtained from the Black Warrior Basin at the Littleton Mine (Twin Pine Coal Company), Jefferson County, west-central Alabama. The sample was from the Mary Lee coal zone of the Pottsville Formation (Lower Pennsylvanian). Experiments with three size fractions (45–150 µm, 1–2 mm, and 5–10 mm) of crushed coal were performed at 40 °C and 35 °C over a pressure range of 1.4–6.9 MPa to simulate coalbed methane reservoir conditions in the Black Warrior Basin and provide data relevant for enhanced coalbed methane recovery operations. The following key observations were made: (1) CO2 adsorption on both dry and water-saturated coal is much more rapid than CH4 adsorption; (2) water saturation decreases the rates of CO2 and CH4 adsorption on coal surfaces, but it appears to have minimal effects on the final magnitude of CO2 or CH4 adsorption if the coal is not previously exposed to CO2; (3) retention of adsorbed CO2 on coal surfaces is significant even with extreme pressure cycling; and (4) adsorption is significantly faster for the 45–150 μm size fraction compared to the two coarser fractions.  相似文献   

8.
CO2 injection in unmineable coal seams could be one interesting option for both storage and methane recovery processes. The objective of this study is to compare and model pure gas sorption isotherms (CO2 and CH4) for well-characterised coals of different maturities to determine the most suitable coal for CO2 storage. Carbon dioxide and methane adsorption on several coals have been investigated using a gravimetric adsorption method. The experiments were carried out using both CO2 and CH4 pure gases at 25 °C from 0.1 to 5 MPa (1 to 50 bar). The experimental results were fitted using Temkin's approach but also with the corrected Langmuir's and the corrected Tóth's equations. The two last approaches are more accurate from a thermodynamical point of view, and have the advantage of taking into account the fact that experimental data (isotherms) correspond to excess adsorption capacities. These approaches allow better quantification of the adsorbed gas. Determined CO2 adsorption capacities are from 0.5 to 2 mmol/g of dry coal. Modelling provides also the affinity parameters of the two gases for the different coals. We have shown these parameters determined with adsorption models could be used for classification and first selection of coals for CO2 storage. The affinity ratio ranges from a value close to 1 for immature coals to 41 for high rank coals like anthracites. This ratio allows selecting coals having high CO2 adsorption capacities. In our case, the modelling study of a significant number of coals from various ranks shows that anthracites seem to have the highest CO2 storage capacities. Our study provides high quality affinity parameters and values of CO2 and CH4 adsorption capacities on various coals for the future modelling of CO2 injection in coal seams.  相似文献   

9.
The cylindrical coal samples were subjected to three successive cycles of sorption–desorption processes of a single gas (CO2, CH4). Acoustic emission (AE) and strains were simultaneously recorded during the sorption and desorption processes.Tests were conducted on medium-rank coal from the Upper Silesia Basin, Poland. Follow-up tests for gas sorption–desorption consistently showed significant changes of AE characteristics for re-runs on the same sample. The AE level decreased in each successive test. The most spectacular differences were observed between AE generated during the first cycle of gas sorption and the subsequent cycle. This phenomenon could be due to structural changes in the coal taking place substantially on its first exposure to the sorbate. The AE results indicate, that each cycle of gas sorption–desorption was run on the same coal though with a somewhat different structure.In those tests, the swelling of coal by CO2 or/and CH4 was anisotropic (greater in the direction perpendicular to the bedding plane than parallel) in each cycle of the gas sorption–desorption process.  相似文献   

10.
Presently many research projects focus on the reduction of anthropogenic CO2 emissions. It is intended to apply underground storage techniques such as flue gas injection in unminable coal seams. In this context, an experimental study has been performed on the adsorption of pure CO2 and preferential sorption behavior of flue gas. A coal sample from the Silesian Basin in Poland (0.68% V Rr), measured in the dry and wet state at 353 K has been chosen for this approach. The flue gas used was a custom class industrial flue gas with 10.9% of CO2, 0.01% of CO, 9% of H2, 3.01% of CH4, 3.0% of O2, 0.106% of SO2 and nitrogen as balance.Adsorption isotherms of CO2 and flue gas were measured upto a maximum of 11 MPa using a volumetric method. Total excess sorption capacities for CO2 on dry and wet Silesia coal ranged between 1.9 and 1.3 mmol/g, respectively. Flue gas sorption capacities on dry and wet Silesia coal were much lower and ranged between 0.45 and 0.2 mmol/g, respectively, at pressures of 8 MPa. The low sorption capacity of wet coal has resulted from water occupying some of the more active adsorption sites and hence reducing the heterogeneity of adsorption sites relative to that of dry coal. Desorption tests with flue gas were conducted to study the degree of preferential sorption of the individual components. These experiments indicate that CO2 is by far the prefered sorbing component under both wet and dry conditions. This is followed by CH4. N2 adsorbs very little on the coal in the presence of CO2 and CH4. It is also observed that the adsorption of CO2 onto coal is not significantly hindered by the addition of other gases, other than dilution effect of the pressure.In addition to the sorption experiments, the density of the flue gas mixture has been determined up to 18 MPa at 318 K. A very good precision of these measurements were documented by volumetric methods.  相似文献   

11.
Gas adsorption isotherms of Akabira coals were established for pure carbon dioxide (CO2), methane (CH4), and nitrogen (N2). Experimental data fit well into the Langmuir model. The ratio of sorption capacity of CO2, CH4, and N2 is 8.5:3.5:1 at a lower pressure (1.2 MPa) regime and becomes 5.5:2:1 when gas pressure increases to 6.0 MPa. The difference in sorption capacity of these three gases is explained by differences in the density of the three gases with increasing pressure. A coal–methane system partially saturated with CH4 at 2.4 MPa adsorption pressure was experimentally studied. Desorption behavior of CH4 by injecting pure CO2 (at 3.0, 4.0, 5.0, and 6.0 MPa), and by injecting the CO2–N2 mixture and pure N2 (at 3.0 and 6.0 MPa) were evaluated. Results indicate that the preferential sorption property of coal for CO2 is significantly higher than that for CH4 or N2. CO2 injection can displace almost all of the CH4 adsorbed on coal. When modeling the CH4–CO2 binary and CH2–CO2–N2 ternary adsorption system by using the extended Langmuir (EL) equation, the EL model always over-predicted the sorbed CO2 value with a lower error, while under-predicting the sorbed CH4 with a higher error. A part of CO2 may dissolve into the solid organic structure of coal, besides its competitive adsorption with other gases. According to this explanation, the EL coefficients of CO2 in EL equation were revised. The revised EL model proved to be very accurate in predicting sorbed ratio of multi-component gases on coals.  相似文献   

12.
In order to better understand the spatiotemporal variations and interrelationships of greenhouse gases (GHG), monthly surface fluxes and profile concentrations of GHG (CO2, N2O and CH4) in karst areas in the Guizhou Province, southwest China, were measured from June 2006 to May 2007. GHG fluxes showed high variability, with a range of 460.9?C1,281.2?mg?m?2?h?1 for CO2, ?25.4 to 81.5???g?m?2?h?1 for N2O and ?28.7 to ?274.9???g?m?2?h?1 for CH4, but no obvious seasonal change trends of the fluxes existed. Profile concentrations of CO2, N2O and CH4 varied between 0.5 and 31.5?mL?L?1, 0.273 and 0.734, and 0.1 and 3.5???L?L?1, respectively. In general, concentrations of CO2 and N2O increased with depth, while CH4 had an inverse trend. However, in October, November and January, the reversal of depth patterns of GHG concentrations took place below 15?cm, close to the soil?Crock interface. The spatiotemporal distribution of CO2 in soil profile was significantly positively correlated with that of N2O (p?<?0.05?C0.01) and negatively correlated with that of CH4 (p?<?0.01). The correlation analysis showed that soil temperature and moisture may be responsible for GHG dynamics in the soils, rather than the exchange of GHG between land and atmosphere.  相似文献   

13.
《Applied Geochemistry》2001,16(7-8):895-910
Coalbed gases in the Lower Silesian Coal Basin (LSCB) of Poland are highly variable in both their molecular and stable isotope compositions. Geochemical indices and stable isotope ratios vary within the following ranges: hydrocarbon (CHC) index CHC=CH4/(C2H6+ C3H8) from 1.1 to 5825, wet gas (C2+) index C2+=(C2H6+ C3H8+ C4H10+ C5H12) / (CH4+ C2H6+ C3H8+ C4H10+ C5H12) 100 (%) from 0.0 to 48.3%, CO2–CH4 (CDMI) index CDMI=CO2/(CO2+ CH4) 100 (%) from 0.1 to 99.9%, δ13C(CH4) from −66.1 to −24.6‰, δD(CH4) from −266 to −117‰, δ13C(C2H6) from −27.8 to −22.8‰, and δ13C(CO2) from −26.6 to 16.8‰. Isotopic studies reveal the presence of 3 genetic types of natural gases: thermogenic (CH4, higher gaseous hydrocarbons, and CO2), endogenic CO2, and microbial CH4 and CO2. Thermogenic gases resulted from coalification processes, which were probably completed by Late Carboniferous and Early Permian time. Endogenic CO2 migrated along the deep-seated faults from upper mantle and/or magma chambers. Minor volumes of microbial CH4 and CO2 occur at shallow depths close to the abandoned mine workings. “Late-stage” microbial processes have commenced in the Upper Cretaceous and are probably active at present. However, depth-related isotopic fractionation which has resulted from physical and physicochemical (e.g. diffusion and adsorption/desorption) processes during gas migration cannot be neglected. The strongest rock and gas outbursts occur only in those parts of coal deposits of the LSCB which are dominated by large amounts of endogenic CO2.  相似文献   

14.
CBM and CO2-ECBM related sorption processes in coal: A review   总被引：1，自引：0，他引：1  
This article reviews the state of research on sorption of gases (CO2, CH4) and water on coal for primary recovery of coalbed methane (CBM), secondary recovery by an enhancement with carbon dioxide injection (CO2-ECBM), and for permanent storage of CO2 in coal seams.Especially in the last decade a large amount of data has been published characterizing coals from various coal basins world-wide for their gas sorption capacity. This research was either related to commercial CBM production or to the usage of coal seams as a permanent sink for anthropogenic CO2 emissions. Presently, producing methane from coal beds is an attractive option and operations are under way or planned in many coal basins around the globe. Gas-in-place determinations using canister desorption tests and CH4 isotherms are performed routinely and have provided large datasets for correlating gas transport and sorption properties with coal characteristic parameters.Publicly funded research projects have produced large datasets on the interaction of CO2 with coals. The determination of sorption isotherms, sorption capacities and rates has meanwhile become a standard approach.In this study we discuss and compare the manometric, volumetric and gravimetric methods for recording sorption isotherms and provide an uncertainty analysis. Using published datasets and theoretical considerations, water sorption is discussed in detail as an important mechanisms controlling gas sorption on coal. Most sorption isotherms are still recorded for dry coals, which usually do not represent in-seam conditions, and water present in the coal has a significant control on CBM gas contents and CO2 storage potential. This section is followed by considerations of the interdependence of sorption capacity and coal properties like coal rank, maceral composition or ash content. For assessment of the most suitable coal rank for CO2 storage data on the CO2/CH4 sorption ratio data have been collected and compared with coal rank.Finally, we discuss sorption rates and gas diffusion in the coal matrix as well as the different unipore or bidisperse models used for describing these processes.This review does not include information on low-pressure sorption measurements (BET approach) to characterize pore sizes or pore volume since this would be a review of its own. We also do not consider sorption of gas mixtures since the data base is still limited and measurement techniques are associated with large uncertainties.  相似文献   

15.
The δ13C values of dissolved HCO3? in 75 water samples from 15 oil and gas fields (San Joaquin Valley, Calif., and the Houston-Galveston and Corpus Christi areas of Texas) were determined to study the sources of CO2 of the dissolved species and carbonate cements that modify the porosity and permeability of many petroleum reservoir rocks. The reservoir rocks are sandstones which range in age from Eocene through Miocene. The δ13C values of total HCO3? indicate that the carbon in the dissolved carbonate species and carbonate cements is mainly of organic origin.The range of δ13C values for the HCO3? of these waters is ?20–28 per mil relative to PDB. This wide range of δ13C values is explained by three mechanisms. Microbiological degradation of organic matter appears to be the dominant process controlling the extremely low and high δ13C values of HCO3? in the shallow production zones where the subsurface temperatures are less than 80°C. The extremely low δ13C values (< ?10 per mil) are obtained in waters where concentrations of SO42? are more than 25 mg/l and probably result from the degradation of organic acid anions by sulfate-reducing bacteria (SO42? + CH3COO? → 2HCO3? + HS?). The high δ13C values probably result from the degradation of these anions by methanogenic bacteria (CH3COO? + H2OaiHCO3? + CH4).Thermal decarboxylation of short-chain aliphatic acid anions (principally acetate) to produce CO2 and CH4 is probably the major source of CO2 for production zones with subsurface temperatures greater than 80°C. The δ13C values of HCO3? for waters from zones with temperatures greater than 100°C result from isotopic equilibration between CO2 and CH4. At these high temperatures, δ13C values of HCO3? decrease with increasing temperatures and decreasing concentrations of these acid anions.  相似文献   

16.
We estimated CO2 and CH4 emissions from mangrove-associated waters of the Andaman Islands by sampling hourly over 24 h in two tidal mangrove creeks (Wright Myo; Kalighat) and during transects in contiguous shallow inshore waters, immediately following the northeast monsoons (dry season) and during the peak of the southwest monsoons (wet season) of 2005 and 2006. Tidal height correlated positively with dissolved O2 and negatively with pCO2, CH4, total alkalinity (TAlk) and dissolved inorganic carbon (DIC), and pCO2 and CH4 were always highly supersaturated (330–1,627 % CO2; 339–26,930 % CH4). These data are consistent with a tidal pumping response to hydrostatic pressure change. There were no seasonal trends in dissolved CH4 but pCO2 was around twice as high during the 2005 wet season than at other times, in both the tidal surveys and the inshore transects. Fourfold higher turbidity during the wet season is consistent with elevated net benthic and/or water column heterotrophy via enhanced organic matter inputs from adjacent mangrove forest and/or the flushing of CO2-enriched soil waters, which may explain these CO2 data. TAlk/DIC relationships in the tidally pumped waters were most consistent with a diagenetic origin of CO2 primarily via sulphate reduction, with additional inputs via aerobic respiration. A decrease with salinity for pCO2, CH4, TAlk and DIC during the inshore transects reflected offshore transport of tidally pumped waters. Estimated mean tidal creek emissions were ～23–173 mmol m?2 day?1 CO2 and ～0.11–0.47 mmol m?2 day?1 CH4. The CO2 emissions are typical of mangrove-associated waters globally, while the CH4 emissions fall at the low end of the published range. Scaling to the creek open water area (2,700 km2) gave total annual creek water emissions ～3.6–9.2?×?1010 mol CO2 and 3.7–34?×?107 mol CH4. We estimated emissions from contiguous inshore waters at ～1.5?×?1011 mol CO2?year?1 and 2.6?×?108 mol CH4?year?1, giving total emissions of ～1.9?×?1011 mol CO2?year?1 and ～3.0?×?108 mol CH4?year?1 from a total area of mangrove-influenced water of ～3?×?104 km2. Evaluating such emissions in a range of mangrove environments is important to resolving the greenhouse gas balance of mangrove ecosystems globally. Future such studies should be integral to wider quantitative process studies of the mangrove carbon balance.  相似文献   

17.
Characterization of coal reservoirs and determination of in-situ physical coal properties related to transport mechanism are complicated due to having lack of standard procedures in the literature. By considering these difficulties, a new approach has been developed proposing the usage of relationships between coal rank and physical coal properties. In this study, effects of shrinkage and swelling (SS) on total methane recovery at CO2 breakthrough (TMRB), which includes ten-year primary methane recovery and succeeding enhanced coalbed methane (ECBM) recovery up to CO2 breakthrough, and CO2 sequestration have been investigated by using rank-dependent coal properties. In addition to coal rank, different coal reservoir types, molar compositions of injected fluid, and parameters within the extended Palmer & Mansoori (P&M) permeability model were considered. As a result of this study, shrinkage and swelling lead to an increase in TMRB. Moreover, swelling increased CO2 breakthrough time and decreased displacement ratio and CO2 storage for all ranks of coal. Low-rank coals are affected more negatively than high-rank coals by swelling. Furthermore, it was realized that dry coal reservoirs are more influenced by swelling than others and saturated wet coals are more suitable for eliminating the negative effects of CO2 injection. In addition, it was understood that it is possible to reduce swelling effect of CO2 on cleat permeability by mixing it with N2 before injection. However, an economical optimization is required for the selection of proper gas mixture. Finally, it is concluded from sensitivity analysis that elastic modulus is the most important parameter, except the initial cleat porosity, controlling SS in the extended P&M model by highly affecting TMRB.  相似文献   

18.
Numerical modelling of the processes of CO2 storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO2 and CH4 were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VRr=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to 3 mm at temperatures of 45 and 32 °C, using a volumetric experimental setup. CO2 sorption was consistently faster than CH4 sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than 2 with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions.Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO2 and CH4 that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated.Further, it was shown that an upscaling of the experimental and modelling results for CO2 and CH4 can be achieved by performing experiments on different grain size fractions under the same experimental conditions.In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.  相似文献   

19.
One of the proposals for large-scale sequestration of fossil fuel-derived CO2 is deep geologic disposal in depleted oil/gas reservoirs or deep aquifers. Previously published scenarios for this inadequately proven technology have either ignored or dismissed the possibility of vertical migration of gases caused by overpressure. Overpressuring of a reservoir or aquifer will be necessary in order to have acceptable rates for dispersal of injected CO2. This research describes methodology and the results of measurement of microseepage of CO2 and CH4 at a large-scale CO2-enhanced oil recovery (EOR) operation at Rangely, Colorado, USA. Shallow and deep soil gas concentrations, and direct transport of CO2 and CH4 into the atmosphere were measured. The interpretation of the measurements was complemented by both stable and radiogenic isotopic measurements of C. The results have demonstrated an estimated microseepage to the atmosphere of approximately 400 metric tonnes of CH4/a from the 78 km2 area of the Rangely field. Preliminary estimates of deep-sourced CO2 losses are <3800 tonnes/a, based on stable isotope measurements of soil gases. Several holes up to 10 m deep were drilled on, and off the field for nested gas sampling of composition and stable C isotopic ratios for CO2 and CH4. Carbon-14 measurements on CO2 from these holes indicate that deep-sourced CO2 microseepage losses were approximately 170 tonnes/a.  相似文献   

20.
Studying gas transport mechanisms in coal seams is crucial in determining the suitability of coal formations for geosequestration and/or CO2-enhanced coal bed methane recovery (ECBM), estimating CO2 storage capacity and recoverable volume of methane, and predicting the long-term integrity of CO2 storage and possible leakages. Due to the dual porosity nature of coal, CO2 transport is a combination of viscous flow and Fickian diffusion. Moreover, CO2 is adsorbed by the coal which leads to coal swelling which can change the porous structure of coal and consequently affects the gas flow properties of coal, i.e. its permeability. In addition, during CO2 permeation, the coal seam undergoes a change in effective stress due to the pore pressure alteration and this can also change the permeability of the coal seam. In addition, depending on the in situ conditions of the coal seam and the plan of the injection scheme, carbon dioxide can be in a supercritical condition which increases the complexity of the problem. We provide an overview of the recent studies on porous structure of coal, CO2 adsorption onto coal, mechanisms of CO2 transport in coalbeds and their measurement, and hydro-mechanical response of coal to CO2 injection and identify opportunities for future research.  相似文献   

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