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.     

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。     

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.     

莺歌海盆地乐东区片钠铝石特征及其对浅层CO2充注的指示

作为天然CO₂的示踪矿物,片钠铝石的形成与CO₂充注密切相关.莺歌海盆地乐东区乐东X构造莺歌海组-黄流组CO₂气藏内发育含片钠铝石砂岩,在开展的岩石学和地球化学研究基础上,确定了研究区片钠铝石的产状和纵向分布特征,分析了形成片钠铝石的“碳来源”和气水条件,进而探讨了与片钠铝石具有成因联系的CO₂的成因.乐东X构造含片钠铝石砂岩为细—极细粒长石石英砂岩和岩屑石英砂岩,片钠铝石主要以充填孔隙及交代颗粒的形式产出,是成岩共生序列中形成较晚的自生矿物之一.在纵向上,片钠铝石仅集中发育于高含CO₂气层的底部以及其下的水层中,这一分布特征以地质实例的形式证实了片钠铝石的形成需要水的参与.研究区浅层CO₂充注后形成的碳酸盐矿物为片钠铝石和铁白云石.片钠铝石的碳氧同位素特征表明形成片钠铝石的“碳”与LDX构造气层中CO₂具有相同的碳来源,以无机幔源成因CO₂为主.红河断裂以及莺歌海盆地中央坳陷内一系列底辟构造及伴生的垂向裂隙可能为CO₂的运移通道.      

CO2 solubility in Martian basalts and Martian atmospheric evolution

To understand possible volcanogenic fluxes of CO₂ to the Martian atmosphere, we investigated experimentally carbonate solubility in a synthetic melt based on the Adirondack-class Humphrey basalt at 1-2.5 GPa and 1400-1625 °C. Starting materials included both oxidized and reduced compositions, allowing a test of the effect of iron oxidation state on CO₂ solubility. CO₂ contents in experimental glasses were determined using Fourier transform infrared spectroscopy (FTIR) and Fe³⁺/Fe^T was measured by Mössbauer spectroscopy. The CO₂ contents of glasses show no dependence on Fe³⁺/Fe^T and range from 0.34 to 2.12 wt.%. For Humphrey basalt, analysis of glasses with gravimetrically-determined CO₂ contents allowed calibration of an integrated molar absorptivity of 81,500 ± 1500 L mol⁻¹ cm⁻² for the integrated area under the carbonate doublet at 1430 and 1520 cm⁻¹. The experimentally determined CO₂ solubilities allow calibration of the thermodynamic parameters governing dissolution of CO₂ vapor as carbonate in silicate melt, K_II, (Stolper and Holloway, 1988) as follows: , ΔV⁰ = 20.85 ± 0.91 cm³ mol⁻¹, and ΔH⁰ = −17.96 ± 10.2 kJ mol⁻¹. This relation, combined with the known thermodynamics of graphite oxidation, facilitates calculation of the CO₂ dissolved in magmas derived from graphite-saturated Martian basalt source regions as a function of P, T, and f_O2. For the source region for Humphrey, constrained by phase equilibria to be near 1350 °C and 1.2 GPa, the resulting CO₂ contents are 51 ppm at the iron-wüstite buffer (IW), and 510 ppm at one order of magnitude above IW (IW + 1). However, solubilities are expected to be greater for depolymerized partial melts similar to primitive shergottite Yamato 980459 (Y 980459). This, combined with hotter source temperatures (1540 °C and 1.2 GPa) could allow hot plume-like magmas similar to Y 980459 to dissolve 240 ppm CO₂ at IW and 0.24 wt.% of CO₂ at IW + 1. For expected magmatic fluxes over the last 4.5 Ga of Martian history, magmas similar to Humphrey would only produce 0.03 and 0.26 bars from sources at IW and IW + 1, respectively. On the other hand, more primitive magmas like Y 980459 could plausibly produce 0.12 and 1.2 bars at IW and IW + 1, respectively. Thus, if typical Martian volcanic activity was reduced and the melting conditions cool, then degassing of CO₂ to the atmosphere may not be sufficient to create greenhouse conditions required by observations of liquid surface water. However, if a significant fraction of Martian magmas derive from hot and primitive sources, as may have been true during the formation of Tharsis in the late Noachian, that are also slightly oxidized (IW + 1.2), then significant contribution of volcanogenic CO₂ to an early Martian greenhouse is plausible.     

CO2 in haplo-phonolite melt: solubility, speciation and carbonate complexation

CO₂ solubility was measured in a synthetic iron-free phonolite (haplo-phonolite) by equilibrating melt with excess CO₂ fluid in a piston cylinder apparatus for a range of pressures (1.0- 2.5 GPa) and temperatures (1300 to 1550°C). The quenched glasses were then analysed using a bulk carbon analytical method (LECO). The measured solubilities are between 0.65 and 2.77 wt.% for the range of conditions studied and show a negative correlation with temperature as reported for most other silicate melt compositions.A range of carbonate species are present within the glass, as well as minor amounts of molecular CO₂. FTIR and NMR analyses suggest that carbonate is present as both ‘network’ and ‘depolymerised’ units as shown for relatively highly polymerised compositions in the model of Brooker et al. (2001b). The bulk CO₂ analyses were used to calibrate the IR extinction coefficient for the carbonate groups. However, the results show that the values obtained for the glasses vary with the melt equilibration conditions, presumably because the ratio of the different carbonate species changes as a complex function of run pressure, temperature and quench rate. Thus the use of IR may not be a reliable method for the quantification of dissolved CO₂ concentrations in natural glasses of ‘intermediate’ composition.     

Rhondonite solubility and thermodynamic properties of aqueous MnCl2 in the system MnOSiO2HClH2O

The solubility of rhodonite, represented by the reaction MnSiO₃ (rhodonite) + 2HCl⁰ = MnCl₂⁰ + SiO₂ (quartz) + H₂O, was investigated experimentally in the temperature range 400°–700°C at 1 and 2 kbar by rapid-quench hydrothermal techniques and the Ag-AgCl buffer methods. Variations in the molalities of associated hydrogen chloride (m_HCl⁰) as a function of the molalities of total Mn indicate that Mn in the fluid in equilibrium with the assemblage rhodonite + quartz is predominantly associated as MnCl₂⁰. The Mn:Cl in the fluid ?2, indicating that Mn⁺² is the dominant oxidation state.The solubility data were used to calculate the equilibrium constant of the above reaction as a function of temperature, pressure, and the difference in Gibbs free energy of formation between MnCl₂⁰ and HCl⁰. The equilibrium constants of solubility for Mn minerals for which thermochemical data are available were also calculated. Calculated mineral solubilities were used in conjunction with the data of Frantz et al. (1981) to calculate the composition of supercritical fluids in equilibrium with Mn-bearing phases and assemblages. At 400°C and 1000 bars, supercritical fluids in equilibrium with olivines of compositions similar to those present in MORB tend to be enriched in Mn, despite the low mole fraction of tephroite in the olivine. Supercritical fluids in equilibrium with the assemblage quartz-hematite-rhodonite at 500° and 400°C and 1000 bars show high concentrations of Mn relative to Fe. Manganese concentrations in the fluids increase with decrease in the mole fraction of H, whereas Fe concentrations decrease. The data indicate that H fugacity plays a significant role in the separation of Mn from Fe in chloride-bearing hydrothermal fluids at supercritical temperatures.     

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.     

Some thermodynamic properties of the Berman and Brown model for CaO-Al2O3-SiO2

The and (1984) excess free energy model (B&B) is extremely convenient to use in modelling multicomponent solutions. However, spinodal calculations reveal that their calibration of this model for CaO-Al₂O₃-SiO₂ produces liquation tielines that do not appear to be in agreement with experimental work. In addition, their calibration contains some strongly negative excess entropy parameters and these permit a most unusual inverted liquation field to start at approximately >2115°C, wt% (SiO₂, Al₂O₃, CaO) = (70, 16, 14). This inverted field expands rapidly to cover most of the ternary for T> 2300°C and continues to expand at all higher temperatures. The Berman and Brown calibration for this system carries these negative excess entropies of mixing because the solution model is very strongly asymmetric as a result of the use of normal oxide mole weights in modelling the configurational entropy of mixing. A suggestion is made for a fairly natural restriction on the relative sizes of empirical models for excess versus configurational entropy.

Expressions are presented for the general consolute condition (all solution models) and for the second and third partials of the B&B G^x model.     

CO2 solubility and speciation in intermediate (andesitic) melts: the role of H2O and composition

We determined total CO₂ solubilities in andesite melts with a range of compositions. Melts were equilibrated with excess C-O(-H) fluid at 1 GPa and 1300°C then quenched to glasses. Samples were analyzed using an electron microprobe for major elements, ion microprobe for C-O-H volatiles, and Fourier transform infrared spectroscopy for molecular H₂O, OH⁻, molecular CO₂, and CO₃²⁻. CO₂ solubility was determined in hydrous andesite glasses and we found that H₂O content has a strong influence on C-O speciation and total CO₂ solubility. In anhydrous andesite melts with ∼60 wt.% SiO₂, total CO₂ solubility is ∼0.3 wt.% at 1300°C and 1 GPa and total CO₂ solubility increases by about 0.06 wt.% per wt.% of total H₂O. As total H₂O increases from ∼0 to ∼3.4 wt.%, molecular CO₂ decreases (from 0.07 ± 0.01 wt.% to ∼0.01 wt.%) and CO₃²⁻ increases (from 0.24 ± 0.04 wt.% to 0.57 ± 0.09 wt.%). Molecular CO₂ increases as the calculated mole fraction of CO₂ in the fluid increases, showing Henrian behavior. In contrast, CO₃²⁻ decreases as the calculated mole fraction of CO₂ in the fluid increases, indicating that CO₃²⁻ solubility is strongly dependent on the availability of reactive oxygens in the melt. These findings have implications for CO₂ degassing. If substantial H₂O is present, total CO₂ solubility is higher and CO₂ will degas at relatively shallow levels compared to a drier melt. Total CO₂ solubility was also examined in andesitic glasses with additional Ca, K, or Mg and low H₂O contents (<1 wt.%). We found that total CO₂ solubility is negatively correlated with (Si + Al) cation mole fraction and positively correlated with cations with large Gibbs free energy of decarbonation or high charge-to-radius ratios (e.g., Ca). Combining our andesite data with data from the literature, we find that molecular CO₂ is more abundant in highly polymerized melts with high ionic porosities (>∼48.3%), and low nonbridging oxygen/tetrahedral oxygen (<∼0.3). Carbonate dominates most silicate melts and is most abundant in depolymerized melts with low ionic porosities, high nonbridging oxygen/tetrahedral oxygen (>∼0.3), and abundant cations with large Gibbs free energy of decarbonation or high charge-to-radius ratio. In natural silicate melt, the oxygens in the carbonate are likely associated with tetrahedral and network-modifying cations (including Ca, H, or H-bonds) or a combinations of those cations.     

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.     

Dissolution of basalts and peridotite in seawater, in the presence of ligands, and CO2: Implications for mineral sequestration of carbon dioxide

Steady-state silica release rates (r_Si) from basaltic glass and crystalline basalt of similar chemical composition as well as dunitic peridotite have been determined in far-from-equilibrium dissolution experiments at 25 °C and pH 3.6 in (a) artificial seawater solutions under 4 bar pCO₂, (b) varying ionic strength solutions, including acidified natural seawater, (c) acidified natural seawater of varying fluoride concentrations, and (d) acidified natural seawater of varying dissolved organic carbon concentrations. Glassy and crystalline basalts exhibit similar r_Si in solutions of varying ionic strength and cation concentrations. Rates of all solids are found to increase by 0.3-0.5 log units in the presence of a pCO₂ of 4 bar compared to CO₂ pressure of the atmosphere. At atmospheric CO₂ pressure, basaltic glass dissolution rates were most increased by the addition of fluoride to solution whereas crystalline basalt rates were most enhanced by the addition of organic ligands. In contrast, peridotite does not display any significant ligand-promoting effect, either in the presence of fluoride or organic acids. Most significantly, Si release rates from the basalts are found to be not more than 0.6 log units slower than corresponding rates of the peridotite at all conditions considered in this study. This difference becomes negligible in seawater suggesting that for the purposes of in-situ mineral sequestration, CO₂-charged seawater injected into basalt might be nearly as efficient as injection into peridotite.     

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.     

Solubility of NaCl in CO2 at high pressure and temperature: First experimental measurements

NaCl solubility in gaseous carbon dioxide has been measured in the pressure range from 30 to 70 MPa at 623 and 673 K. Our originally-designed high pressure apparatus allows in situ sampling of a portion of the fluid phase for chemical analysis. The results indicate that the solubility of NaCl increases with both temperature and pressure, and is about 4-5 orders of magnitude higher than saturated NaCl pressure values at the same temperature conditions (6.02 × 10⁻¹² at 623 K and 1.51 × 10⁻¹⁰ at 673 K). It is also 1-2 orders of magnitude greater than predictions according to the Equation of State of the ternary H₂O-CO₂-NaCl system by Duan, Moeller and Weare [Duan, Z., Moller, N., and Weare, J. H. (1995) Equation of state for the NaCl-H₂O-CO₂ system: prediction of phase equilibria and volumetric properties. Geochim. Cosmochim. Acta59, 2869] and has the opposite pressure dependence. The activity values of NaCl in the vapor phase, calculated from the experiments (with pure molten NaCl as a standard state in the vapor), have been fitted to the Darken Quadratic Formalism: , where, x_NaCl,v is mole the fraction of NaCl in the vapor phase, , , where P is the pressure in MPa and T the absolute temperature. Caution should be exerted while extrapolating this empirical equation far beyond the experimental P-T-compositional range.     

CO2 degassing and trapping during hydrothermal cycles related to Gondwana rifting in eastern Australia

Intensive carbonate and clay mineral authigenesis took place throughout the Late Permian Bowen-Gunnedah-Sydney basin system in eastern Australia. We conducted isotopic and trace element analyses of carbonate and clay minerals from clastic sedimentary rocks of the Gunnedah Basin and the Denison Trough in the Bowen Basin. Rb-Sr isochron age data of the illitic clays are consistent with episodic hydrothermal fluid flow events that occurred in association with Gondwana rifting accompanied by alkaline magmatism at ∼85 Ma and ∼95 Ma. Stable isotope data of carbonate and clay minerals from the Gunnedah Basin are indicative of meteoric waters from a high-latitude environment as the main fluid source, whereas trace element, Sr and Nd isotope data highlight mixing of meteoric fluids with magmatic and/or crustal components, with a possible input from marine carbonates for some samples. Trace metals, oxygen and strontium isotopes of dawsonites from the Denison Trough are interpreted to have been mobilised by fluids that interacted with evolved clastic sedimentary and marine carbonate end members. According to the carbon isotope data, CO₂ for calcite and ankerite precipitation was sourced mainly from thermal degradation of organic matter and magmatism, whereas the CO₂ used for dawsonite formation is inferred to have been derived from magmatic and marine sources. In the low permeability environments (particularly in coal seams), the increasing accumulation and oversaturation of CO₂ particularly promote the precipitation of dawsonite.     

A general algorithm for the O abundance correction to C/C determinations from CO2 isotopologue measurements, including CO2 characterised by ‘mass-independent’ oxygen isotope distributions

It is widely recognised that a significant limitation to the ultimate precision of carbon stable isotope ratio measurements, as obtained from dual-inlet mass spectrometric measurements of CO₂ isotopologue ion abundances at m/z 44, 45, and 46, is the correction for interference from ¹⁷O-bearing molecular ions. Two long-established, alternative procedures for determining the magnitude of this correction are in widespread use (although only one has IAEA approval); their differences lead to small but potentially significant discrepancies in the magnitude of the resulting correction. Furthermore, neither approach was designed to accommodate oxygen three-isotope distributions which do not conform to terrestrial mass-dependent behaviour. Stratospheric CO₂, for example, contains a strongly ‘mass-independent’ oxygen isotope composition. A new strategy for determining the ¹⁷O-bearing ion correction is presented, for application where the oxygen three-isotope characteristics of the analyte CO₂ are accurately known (or assigned) in terms of the slope λ of the three-isotope fractionation line and the ordinate axis intercept 10³ ln(1 + k) on a 10³ ln(1 + δ¹⁷O) versus 10³ ln(1 + δ¹⁸O) plot. At the heart of the approach is the relationship between ¹⁷R, which is the ¹⁷O/¹⁶O ratio of the sample CO₂, and other assigned or empirically determined parameters needed for the δ¹³C evaluation:

     

Feldspar dissolution rates measured using phase-shift interferometry: Implications to CO2 underground sequestration

To assess CO₂ underground sequestration from a geochemical viewpoint, the anorthite dissolution rate, which is an important parameter of risk analysis, was measured in a CO₂–water system. The authors sought to obtain precise dissolution rate data in a short time observing a crystal surface on a nanoscale. For this purpose, phase-shift interferometry was applied. Using this method, uncertainty of the reactive surface area that is imparted on calculation of the dissolution rate constant can also be avoided. The time-course profile of vertical retreat of the surface revealed that the anorthite dissolution process changes from the initial transient state to a later steady state, which is consistent with results of numerous precedent studies. The transient dissolution rate depends strongly on local features (e.g., density of defects, variation of chemical compositions) of the crystal surface, rather than on temperature. Therefore, it is very important to determine the original properties of the anorthite surface for the examination of subsequent dissolution process. Contrary to general expectations, the anorthite dissolution can alter the physical properties of reservoir rock immediately after CO₂ injection. The simple estimation using the anorthite dissolution rate obtained in this study, which was done as a test case for the CO₂ underground sequestration project conducted by RITE, revealed that porosity of reservoir rock increased about 2% (23–23.4%) of initial values during 60 a. That change in physical property in such a short time might enhance the diffusion of injected CO₂ and formation water, and therefore accelerate further geochemical reactions. Results of this study demonstrate that the geochemical water–rock interaction, which is generally regarded as a longer-term phenomenon than various physical processes, can also affect the reservoir system from the initial stage.     

火山岩吸附CO2气的成藏潜力及实例分析

火山岩的脱气实验和对昌德东CO2气藏气源的分析结果表明加热火山岩到250℃时,脱出挥发分总量为0.0299～0.0790mL/g,其中CO2脱出量为0.0218～0.0706mL/g(0.429～1.387wt%);挥发组分以CO2为主,还含有H2、CO、CH4等还原性气体,以及少量低碳烷烃,CO2含量和总烃呈现反比关系;基性岩的CO2脱出量、脱出率高于中、酸性岩;CO2脱出量与岩石碱质含量正相关.松辽盆地北部昌德东CO2气藏成藏模式为"自生自储",成藏CO2气主要来自深部被火山岩吸附的气.随岩浆上升,在岩浆冷凝成火山岩的过程中被吸附于火山岩的节理、劈理和晶体位错之中的CO2气,连同火山岩包体中的残留气,成为高纯CO2气藏的主要补给源,并非地幔气体沿大断裂上来直接充注成藏.     

Flue gas and pure CO2 sorption properties of coal: A comparative study

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.     

Mitigation of asphaltics deposition during CO2 flood by enhancing CO2 solvency with chemical modifiers

CO₂ injected in the reservoir of McElroy Field, TX, for a CO₂ flood was in the supercritical state. Supercritical CO₂ fluid is capable of extracting light and intermediate hydrocarbons from rocks but is unable to extract heavy hydrocarbons and asphaltics. Therefore, plugging of asphaltics in reservoir rocks and a consequent reduction in injectivity and recovery may result when CO₂ only is used in enhanced oil recovery. By adding common solvents as chemical modifiers, the flooding fluid shows marked improvement in solvency for heavy components of crudes due to its increased density and polarity. Numerous supercritical CO₂ fluid extractions of dolomite rock from the Grayburg Formation containing known amount of spiked McElroy crude oil have been carried out to evaluate extraction efficiencies of CO₂ and CO₂ with chemical modifiers at various temperatures and pressures. All experiments show that extraction efficiency increases with increasing CO₂ pressure but decreases with increasing temperature. Addition of chemical modifiers to CO₂ also shows improved extraction efficiency and reduced asphaltic deposits. Under the pressure and temperature similar to McElroy reservoir conditions; chemically modified CO₂ yielded almost 3 times as much oil extracts as those in extractions with CO₂ only. It also reduced the asphaltics content in extracted rocks to nearly one half; indicating its potential for mitigating asphaltics plugging of formation rocks