鄂尔多斯盆地山西组地下咸水CO2溶解能力

实施CO₂的地质储存是目前公认的减缓全球变暖的有效途径之一.潜在的储存场所包括衰竭的油气藏、深部不可开采煤层及深部咸水层.其中, 深部咸水层储存潜力最大.在发挥作用的诸多机理中, 溶解埋存具有埋存量大、作用时间较长以及安全性高的特点.在评价深部咸水含水层CO₂溶解储存潜力时, 溶解度是一个关键参数.提出了测定咸水含水层地层水CO₂溶解度的方法, 并将其实际应用于鄂尔多斯盆地山西组地层水.鄂尔多斯盆地是我国重要的能源基地, CO₂排放量大, 排放浓度高.采集了野外实地水样, 进行了化学成分分析, 并人工合成该水样; 测定了40~80 ℃、8~12 MPa条件下CO₂在该水样中的溶解度, 其结果可为评价鄂尔多斯盆地深部咸水含水层埋存能力提供依据.      

Oxygen isotope exchange between H2O and CO2 at elevated CO2 pressures: Implications for monitoring of geological CO2 storage

Traditionally, the application of stable isotopes in Carbon Capture and Storage (CCS) projects has focused on δ¹³C values of CO₂ to trace the migration of injected CO₂ in the subsurface. More recently the use of δ¹⁸O values of both CO₂ and reservoir fluids has been proposed as a method for quantifying in situ CO₂ reservoir saturations due to O isotope exchange between CO₂ and H₂O and subsequent changes in δ¹⁸O_H2O values in the presence of high concentrations of CO₂. To verify that O isotope exchange between CO₂ and H₂O reaches equilibrium within days, and that δ¹⁸O_H2O values indeed change predictably due to the presence of CO₂, a laboratory study was conducted during which the isotope composition of H₂O, CO₂, and dissolved inorganic C (DIC) was determined at representative reservoir conditions (50 °C and up to 19 MPa) and varying CO₂ pressures. Conditions typical for the Pembina Cardium CO₂ Monitoring Pilot in Alberta (Canada) were chosen for the experiments. Results obtained showed that δ¹⁸O values of CO₂ were on average 36.4 ± 2.2‰ (1σ, n = 15) higher than those of water at all pressures up to and including reservoir pressure (19 MPa), in excellent agreement with the theoretically predicted isotope enrichment factor of 35.5‰ for the experimental temperatures of 50 °C. By using ¹⁸O enriched water for the experiments it was demonstrated that changes in the δ¹⁸O values of water were predictably related to the fraction of O in the system sourced from CO₂ in excellent agreement with theoretical predictions. Since the fraction of O sourced from CO₂ is related to the total volumetric saturation of CO₂ and water as a fraction of the total volume of the system, it is concluded that changes in δ¹⁸O values of reservoir fluids can be used to calculate reservoir saturations of CO₂ in CCS settings given that the δ¹⁸O values of CO₂ and water are sufficiently distinct.     

高温高压下超临界二氧化碳作用对花岗岩力学性质影响的试验研究

为了研究二氧化碳基增强型地热系统核心及邻近区域中超临界二氧化碳(ScCO₂)作用对岩石力学性能的影响,设计了纯ScCO₂与干燥花岗岩作用,ScCO₂、水蒸气与干燥花岗岩作用,ScCO₂与在水中浸泡了24 h后的花岗岩作用3种试验条件,每种试验条件下均开展了210、240、270℃温度下的试验。对ScCO₂作用后的岩样以及一个未经处理的对比样先后开展纵波波速测试以及单轴压缩试验,获得了岩石的纵波波速、单轴抗压强度以及弹性模量。纵波波速试验结果表明,在上述3种试验条件下,花岗岩样的波速会都会发生一定程度的降低。单轴压缩试验结果表明,ScCO₂作用后的岩石单轴抗压强度及弹性模量都几乎没有受到影响,但是从破坏模式看,未经处理的岩石以张拉破坏为主,处理后的岩石以剪切破坏为主,并且随着温度的升高剪切破坏越明显。试验结果说明,在不存在水或者仅有微量水存在的情况下,ScCO₂的作用对岩石产生轻微损伤,岩样的刚性减弱、塑性增强,导致其纵波波速有少量的下...     

Solubility and solution mechanism of H2O in alkali silicate melts and glasses at high pressure and temperature

The solubility behavior of H₂O in melts in the system Na₂O-SiO₂-H₂O was determined by locating the univariant phase boundary, melt = melt + vapor in the 0.8-2 GPa and 1000°-1300°C pressure and temperature range, respectively. The NBO/Si-range of the melts (0.25-1) was chosen to cover that of most natural magmatic liquids. The H₂O solubility in melts in the system Na₂O-SiO₂-H₂O (X_H2O) ranges between 18 and 45 mol% (O = 1) with (∂X_H2O/∂P)_T∼14-18 mol% H₂O/GPa. The (∂X_H2O/∂P)_T is negatively correlated with NBO/Si (= Na/Si) of the melt. The (∂X_H2O/∂T)_P is in the −0.03 to +0.05 mol% H₂O/°C range, and is negatively correlated with NBO/Si. The [∂X_H2O/∂(NBO/Si)]_P,T is in the −3 to −8 mol% H₂O/(NBO/Si) range. Melts with NBO/Si similar to basaltic liquids (∼0.6-∼1.0) show (∂X_H2O/∂T)_P<0, whereas more polymerized melts exhibit (∂X_H2O/∂T)_P>0. Complete miscibility between hydrous melt and aqueous fluid occurs in the 0.8-2 GPa pressure range for melts with NBO/Si ≤0.5 at T >1100°C. Miscibility occurs at lower pressure the more polymerized the melt.     

Fugacities and free energies of CO2 at high pressures and temperatures

Fugacity and free-energy values have been calculated from p-v-t data for CO₂ in the temperature range from 50 to 1000°C, at pressures from 25 to 1400 bars.     

CO2-water-basalt interaction. Numerical simulation of low temperature CO2 sequestration into basalts

The interaction between CO₂-rich waters and basaltic glass was studied using reaction path modeling in order to get insight into the water-rock reaction process including secondary mineral composition, water chemistry and mass transfer as a function of CO₂ concentration and reaction progress (ξ). The calculations were carried out at 25-90 °C and pCO₂ to 30 bars and the results were compared to recent experimental observations and natural systems. A thermodynamic dataset was compiled from 25 to 300 °C in order to simulate mineral saturations relevant to basalt alteration in CO₂-rich environment including revised key aqueous species for mineral dissolution reactions and apparent Gibbs energies for clay and carbonate solid solutions observed to form in nature. The dissolution of basaltic glass in CO₂-rich waters was found to be incongruent with the overall water composition and secondary mineral formation depending on reaction progress and pH. Under mildly acid conditions in CO₂ enriched waters (pH <6.5), SiO₂ and simple Al-Si minerals, Ca-Mg-Fe smectites and Ca-Mg-Fe carbonates predominated. Iron, Al and Si were immobile whereas the Mg and Ca mobility depended on the mass of carbonate formed and water pH. Upon quantitative CO₂ mineralization, the pH increased to >8 resulting in Ca-Mg-Fe smectite, zeolites and calcite formation, reducing the mobility of most dissolved elements. The dominant factor determining the reaction path of basalt alteration and the associated element mobility was the pH of the water. In turn, the pH value was determined by the concentration of CO₂ and extent of reaction. The composition of the carbonates depended on the mobility of Ca, Mg and Fe. At pH <6.5, Fe was in the ferrous oxidation state resulting in the formation of Fe-rich carbonates with the incorporation of Ca and Mg. At pH >8, the mobility of Fe and Mg was limited due to the formation of clays whereas Ca was incorporated into calcite, zeolites and clays. Competing reactions between clays (Ca-Fe smectites) and carbonates at low pH, and zeolites and clays (Mg-Fe smectites) and carbonates at high pH, controlled the availability of Ca, Mg and Fe, playing a key role for low temperature CO₂ mineralization and sequestration into basalts. Several problems of the present model point to the need of improvement in future work. The determinant factors linking time to low temperature reaction path modeling may not only be controlled by the primary dissolving phase, which presents challenges concerning non-stoichiometric dissolution, the leached layer model and reactive surface area, but may include secondary mineral precipitation kinetics as rate limiting step for specific reactions such as retrieved from the present reaction path study.     

Carbon isotope evidence implying high O2/CO2 ratios in the Permo-Carboniferous atmosphere

Theoretical models predict a marked increase in atmospheric O₂ to ∼35% during the Permo-Carboniferous (∼300 Ma) occurring against a low (∼0.03%) CO₂ level. An upper O₂ value of 35%, however, remains disputed because ignition data indicate that excessive global forest fires would have ensued. This uncertainty limits interpretation of the role played by atmospheric oxygen in Late Paleozoic biotic evolution. Here, we describe new results from laboratory experiments with vascular land plants that establish that a rise in O₂ to 35% increases isotopic fractionation (Δ¹³C) during growth relative to control plants grown at 21% O₂. Despite some effect of the background atmospheric CO₂ level on the magnitude of the increase, we hypothesize that a substantial Permo-Carboniferous rise in O₂ could have imprinted a detectable geochemical signature in the plant fossil record. Over 50 carbon isotope measurements on intact carbon from four fossil plant clades with differing physiological ecologies and ranging in age from Devonian to Cretaceous reveal a substantial Δ¹³C anomaly (5‰) occurring between 300 and 250 Ma. The timing and direction of the Δ¹³C excursion is consistent with the effects of a high O₂ atmosphere on plants, as predicted from photosynthetic theory and observed in our experiments. Preliminary calibration of the fossil Δ¹³C record against experimental data yields a predicted O₂/CO₂ mixing ratio of the ancient atmosphere consistent with that calculated from long-term models of the global carbon and oxygen cycles. We conclude that further work on the effects of O₂ in the combustion of plant materials and the spread of wildfire is necessary before existing data can be used to reliably set the upper limit for paleo-O₂ levels.     

Brucite [Mg(OH2)] carbonation in wet supercritical CO2: An in situ high pressure X-ray diffraction study

Understanding mechanisms and kinetics of mineral carbonation reactions relevant to sequestering carbon dioxide as a supercritical fluid (scCO₂) in geologic formations is crucial to accurately predicting long-term storage risks. Most attention so far has been focused on reactions occurring between silicate minerals and rocks in the aqueous dominated CO₂-bearing fluid. However, water-bearing scCO₂ also comprises a reactive fluid, and in this situation mineral carbonation mechanisms are poorly understood. Using in situ high-pressure X-ray diffraction, the carbonation of brucite [Mg(OH)₂] in wet scCO₂ was examined at pressure (82 bar) as a function of water concentration and temperature (50 and 75 °C). Exposing brucite to anhydrous scCO₂ at either temperature resulted in little or no detectable reaction over three days. However, addition of trace amounts of water resulted in partial carbonation of brucite into nesquehonite [MgCO₃·3H₂O] within a few hours at 50 °C. By increasing water content to well above the saturation level of the scCO₂, complete conversion of brucite into nesquehonite was observed. Tests conducted at 75 °C resulted in the conversion of brucite into magnesite [MgCO₃] instead, apparently through an intermediate nesquehonite step. Raman spectroscopy applied to brucite reacted with ¹⁸O-labeled water in scCO₂ show it was incorporated into carbonate at a relatively high concentration. This supports a carbonation mechanism with at least one step involving a direct reaction between the mineral and water molecules without mediation by a condensed aqueous layer.     

Characteristics of high heating rate biomass chars prepared under N2 and CO2 atmospheres

Partial substitution of coal by biomass in combustion systems in conjunction with advanced technologies for CO₂ capture and storage may result in a significant reduction of greenhouse gases emissions. This study investigates three biomass chars produced from rice husk, forest residuals and wood chips under N₂ and CO₂ atmospheres using a drop tube furnace (DTF) heated at 950 °C. The char constitutes an unburned residue which has been devolatilized under conditions resembling in thermal history those in full scale boilers. Higher weight losses were achieved under N₂ than under CO₂ for each type of biomass, and the highest weight loss was that of wood chips biomass, followed by forest residuals and then rice husk. The results indicate significant morphological differences between the biomass chars produced. The wood chips yielded thick-walled chars with a cenospheric shape very similar to those of low-rank vitrinite. The forest residual chars were angular in shape and often had a tenuinetwork structure, while the rice husk chars retained their vegetal structure. Overall, the studied biomass chars can be described as microporous solids. However, in the case of the rice husk, the silica associated to the char walls was essentially mesoporous, increasing the adsorption capacity of the rice husk chars. The atmosphere in the DTF affects the development of porosity in the chars. The pore volumes of the rice husk and forest residual chars prepared under a CO₂ atmosphere were higher than those of chars prepared under a N₂ atmosphere, whereas the opposite was the case with the wood chip chars. The chars that experienced the most drastic devolatilization were those with the lowest intrinsic reactivity. This indicates a more efficient reorganization of the chemical structure that reduces the number of active sites available for oxygen attack. Overall a similar morphology, optical texture, specific surface area and reactivity were found for the biomass chars generated under N₂ and CO₂, which is a similar result to that obtained for coal chars.     

CO2 solubility in dacitic melts equilibrated with H2O-CO2 fluids: Implications for modeling the solubility of CO2 in silicic melts

The solubility of CO₂ in dacitic melts equilibrated with H₂O-CO₂ fluids was experimentally investigated at 1250°C and 100 to 500 MPa. CO₂ is dissolved in dacitic glasses as molecular CO₂ and carbonate. The quantification of total CO₂ in the glasses by mid-infrared (MIR) spectroscopy is difficult because the weak carbonate bands at 1430 and 1530 cm⁻¹ can not be reliably separated from background features in the spectra. Furthermore, the ratio of CO_2,mol/carbonate in the quenched glasses strongly decreases with increasing water content. Due to the difficulties in quantifying CO₂ species concentrations from the MIR spectra we have measured total CO₂ contents of dacitic glasses by secondary ion mass spectrometry (SIMS).At all pressures, the dependence of CO₂ solubility in dacitic melts on x^fluid_CO2,total shows a strong positive deviation from linearity with almost constant CO₂ solubility at x_CO2fluid > 0.8 (maximum CO₂ solubility of 795 ± 41, 1376 ± 73 and 2949 ± 166 ppm at 100, 200 and 500 MPa, respectively), indicating that dissolved water strongly enhances the solubility of CO₂. A similar nonlinear variation of CO₂ solubility with x_CO2fluid has been observed for rhyolitic melts in which carbon dioxide is incorporated exclusively as molecular CO₂ (Tamic et al., 2001). We infer that water species in the melt do not only stabilize carbonate groups as has been suggested earlier but also CO₂ molecules.A thermodynamic model describing the dependence of the CO₂ solubility in hydrous rhyolitic and dacitic melts on T, P, f_CO2 and the mol fraction of water in the melt (x_water) has been developed. An exponential variation of the equilibrium constant K₁ with x_water is proposed to account for the nonlinear dependence of x_CO2,totalmelt on x_CO2fluid. The model reproduces the CO₂ solubility data for dacitic melts within ±14% relative and the data for rhyolitic melts within 10% relative in the pressure range 100-500 MPa (except for six outliers at low x_CO2fluid). Data obtained for rhyolitic melts at 75 MPa and 850°C show a stronger deviation from the model, suggesting a change in the solubility behavior of CO₂ at low pressures (a Henrian behavior of the CO₂ solubility is observed at low pressure and low H₂O concentrations in the melt). We recommend to use our model only in the pressure range 100-500 MPa and in the x_CO2fluid range 0.1-0.95. The thermodynamic modeling indicates that the partial molar volume of total CO₂ is much lower in rhyolitic melts (31.7 cm³/mol) than in dacitic melts (46.6 cm³/mol). The dissolution enthalpy for CO₂ in hydrous rhyolitic melts was found to be negligible. This result suggests that temperature is of minor importance for CO₂ solubility in silicic melts.     

Diffusion and viscosity of Mg2SiO4 liquid at high pressure from first-principles simulations

We investigate two key transport properties, self-diffusion and viscosity, of Mg₂SiO₄ liquid as a function of temperature and pressure using density functional theory-based molecular dynamics method. Liquid dynamics in a 224-atom supercell was captured in equilibrium simulations of relatively long durations (50-300 ps) to obtain an acceptable convergence. Our results show that Mg and Si are, respectively, the most and least mobile species at most conditions studied and all diffusivities become similar at high pressure. With increasing temperature from 2200 to 6000 K at ambient pressure, the self-diffusivities increase by factors of 25 (Mg), 80 (Si) and 65 (O), and the viscosity decreases by a factor of 30. The predicted temperature variations of all transport coefficients closely follow the Arrhenian law. However, their pressure variations show a significant non-Arrhenian behavior and also are sensitive to temperature. At 3000 K, the diffusivity (viscosity) decreases (increases) by more than one order of magnitude between 0 and 50 GPa with their activation volumes increasing on compression. Over the entire mantle pressure range, the variations at 4000 K are of two orders of magnitude with nearly constant activation volumes whereas the variations at 6000 K are within one order of magnitude with decreasing activation volumes. The predicted complex dynamical behavior of Mg₂SiO₄ liquid can be associated with the structural changes occurring on compression. We also estimate the diffusivity and viscosity profiles along a magma ocean isentrope, which suggest that the melt transport properties vary modestly over the relevant magma ocean depth ranges.     

A high temperature equation of state for the H2O-CaCl2 and H2O-MgCl2 systems

An equation of state (EOS) is developed for salt-water systems in the high temperature range. As an example of the applications, this EOS is parameterized for the calculation of density, immiscibility, and the compositions of coexisting phases in the CaCl₂-H₂O and MgCl₂-H₂O systems from 523 to 973 K and from saturation pressure to 1500 bar. All available volumetric and phase equilibrium measurements of these binaries are well represented by this equation. This EOS is based on a Helmholtz free energy representation constructed from a reference system containing hard-sphere and polar contributions plus an empirical correction. For the temperature and pressure range in this study, the electrolyte solutes are assumed to be associated. The water molecules are modeled as hard spheres with point dipoles and the solute molecules, MgCl₂ and CaCl₂, as hard spheres with point quadrupoles. The free energy of the reference system is calculated from an analytical representation of the Helmholtz free energy of the hard-sphere contributions and perturbative estimates of the electrostatic contributions. The empirical correction used to account for deviations of the reference system predictions from measured data is based on a virial expansion. The formalism allows generalization to aqueous systems containing insoluble gases (CO₂, CH₄), alkali chlorides (NaCl, KCl), and alkaline earth chlorides (CaCl₂, MgCl₂). The program of this model is available as an electronic annex (see EA1 and EA2) and can also be downloaded at: http://www.geochem-model.org/programs.htm.     

GEOCARBSULF: A combined model for Phanerozoic atmospheric O2 and CO2

A model for the combined long-term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the GEOCARB III model [Berner R.A., Kothavala Z., 2001. GEOCARB III: a revised model of atmospheric CO₂ over Phanerozoic time. Am. J. Sci. 301, 182-204] for CO₂ with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for O₂ [Berner R.A., 2001. Modeling atmospheric O₂ over Phanerozoic time. Geochim. Cosmochim. Acta65, 685-694]. New isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models. Sensitivity analysis is done by determining (1) the effect on weathering rates of using rapid recycling (rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks); (2) the effect on O₂ of using different initial starting conditions; (3) the effect on O₂ of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic δ¹³C for the past 200 million years; (4) the effect on sulfur isotope fractionation and on O₂ of varying the size of O₂ feedback during sedimentary pyrite formation; (5) the effect on O₂ of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion, and the degree of exposure of coastal lands by sea level change; (6) the effect on CO₂ of adding the variability of volcanic rock weathering over time [Berner, R.A., 2006. Inclusion of the weathering of volcanic rocks in the GEOCARBSULF model. Am. J. Sci.306 (in press)]. Results show a similar trend of atmospheric CO₂ over the Phanerozoic to the results of GEOCARB III, but with some differences during the early Paleozoic and, for variable volcanic rock weathering, lower CO₂ values during the Mesozoic. Atmospheric oxygen shows a major broad late Paleozoic peak with a maximum value of about 30% O₂ in the Permian, a secondary less-broad peak centered near the Silurian/Devonian boundary, variation between 15% and 20% O₂ during the Cambrian and Ordovician, a very sharp drop from 30% to 15% O₂ at the Permo-Triassic boundary, and a more-or less continuous rise in O₂ from the late Triassic to the present.     

CO2分压条件下煤中矿物质溶解度数值模拟

查明煤中矿物质在不同温度和CO₂分压条件下溶解度变化规律,能为注入CO₂过程中煤储层渗透率分析提供重要依据。借助水文地球化学模拟软件PHREEQC对在不同温度和CO₂分压条件下煤中各矿物的溶解度进行了水化学模拟,得出不同温度和CO₂分压条件下矿物质溶解度的变化规律。结果表明：在无CO₂分压时,随着温度的升高各矿物的溶解度增加;当溶液中CO₂分压增加到一定程度时,随着温度的升高各矿物的溶解度降低（石英除外）;在温度相同时,随着CO₂分压的增加,所有矿物（石英除外）溶解度均增加,方解石的溶解度随着CO₂分压的升高呈现出迅速增加的趋势,其他矿物随着CO₂分压的升高,溶解度增加的速率较为缓慢。     

Caprock interaction with CO2: A laboratory study of reactivity of shale with supercritical CO2 and brine

Crushed rock from two caprock samples, a carbonate-rich shale and a clay-rich shale, were reacted with a mixture of brine and supercritical CO₂ (CO₂–brine) in a laboratory batch reactor, at different temperature and pressure conditions. The samples were cored from a proposed underground CO₂ storage site near the town of Longyearbyen in Svalbard. The reacting fluid was a mixture of 1 M NaCl solution and CO₂ (110 bar) and the water/rock ratio was 20:1. Carbon dioxide was injected into the reactors after the solution had been bubbled with N₂, in order to mimic O₂-depleted natural storage conditions. A control reaction was also run on the clay-rich shale sample, where the crushed rock was reacted with brine (CO₂-free brine) at the same experimental conditions. A total of 8 batch reaction experiments were run at temperatures ranging from 80 to 250 °C and total pressures of 110 bar (∼40 bar for the control experiment). The experiments lasted 1–5 weeks.Fluid analysis showed that the aqueous concentration of major elements (i.e. Ca, Mg, Fe, K, Al) and SiO₂ increased in all experiments. Release rates of Fe and SiO₂ were more pronounced in solutions reacted with CO₂–brine as compared to those reacted with CO₂-free brine. For samples reacted with the CO₂–brine, lower temperature reactions (80 °C) released much more Fe and SiO₂ than higher temperature reactions (150–250 °C). Analysis by SEM and XRD of reacted solids also revealed changes in mineralogical compositions. The carbonate-rich shale was more reactive at 250 °C, as revealed by the dissolution of plagioclase and clay minerals (illite and chlorite), dissolution and re-precipitation of carbonates, and the formation of smectite. Carbon dioxide was also permanently sequestered as calcite in the same sample. The clay-rich shale reacted with CO₂–brine did not show major mineralogical alteration. However, a significant amount of analcime was formed in the clay-rich shale reacted with CO₂-free brine; while no trace of analcime was observed in either of the samples reacted with CO₂–brine.     

Melting relationships in the systems CaOCO2 and MgOCO2 to 33 kilobars

The melting temperatures of calcite and magnesite in the presence of excess CO₂ have been measured using Ag₂C₂O₄ in sealed capsules m a piston-cylinder apparatus. At 27 kbar, 11.5 wt % CO₂ dissolves in molten CaCO₂, depressing the freezing temperature from 1610 to 1505°C; and 6.5 wt % CO₂ dissolves in molten MgCO₃, depressing the freezing temperature from 1590 to 1510°C. The eutectic between calcite and lime was located at 1385°C at 27 kbar. These and other new results, combined with previously published data, permit completion of PT diagrams for the systems CaO-CO₂ and MgO-CO₂ from 1 bar to 35 kbar. The dissociation curve for each carbonate terminates at an invariant point where melting begins, at 40 bars and 1230°C for CaO-CO₂ and 23 kbar and 1550°C for MgO-CO₂ The differences between the two systems are explained by the different solubilities of CO₂ in the invariant liquids consequent upon the large pressure difference between the locations of these two invariant points. The results show that the temperatures for the beginning of melting of carbonates in the asthenosphere are lowered by about 100°C in the presence of CO₂.     

Selection of coals of different maturities for CO2 Storage by modelling of CH4 and CO2 adsorption isotherms

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.     

First principles molecular dynamics simulations of diopside (CaMgSi2O6) liquid to high pressure

We use first principles molecular dynamics simulations based on density functional theory in the local density approximation to investigate CaMgSi₂O₆ liquid over the entire mantle pressure regime. We find that the liquid structure becomes much more densely packed with increasing pressure, with the mean Si-O coordination number increasing nearly linearly with volume from fourfold near ambient pressure to sixfold at the base of the mantle. Fivefold Si-O coordination environments are most abundant at intermediate compression. The properties of Mg and Si coordination environments are nearly identical to those in MgSiO₃ liquid, whereas Ca is more highly coordinated with larger mean Ca-O bond length as compared with Mg. The density increases smoothly with increasing pressure over the entire range studied. The Grüneisen parameter increases by a factor of three on twofold compression. The density contrast between diopside composition liquid and the isochemical crystalline assemblage is less than 2% at the core mantle boundary, less than that in the case of MgSiO₃. Thermodynamic properties are described in terms of a liquid-state fundamental thermodynamic relation.     

深部咸含水层CO2注入下压力抬升与流体迁移的大尺度模拟研究:以松辽盆地为例

地下深部封存CO2已经被公认是人类削减温室气体排放的一条有效而又科学的途径。深部咸含水层CO2地质封存因封存潜力巨大,技术可行,且已有实际的工程运行,因而备受关注。松辽盆地是中国潜在的CO2储存场地之一,选择松辽盆地为大尺度模拟研究对象,选取姚家组砂岩层为储层,选取嫩江组泥岩为盖层,运用TOUGH-MP并行计算代码建立了覆盖整个松辽盆地的三维地质模型,在中央凹陷区开展大尺度CO2注入模拟研究,包括CO2运移、储存、地层压力提升以及储存安全性等问题。模拟结果表明:持续注入100a后形成的CO2羽远小于产生的压力积聚区影响范围。注入产生的压力抬升将在注入停止后迅速消散,不会对区域地层压力和浅层地下水系统产生显著影响。在千年之内注入的CO2将随着时间持续,逐渐溶解于水中,而不会因盖层微弱的渗透性而逃逸。