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1.
A prognosis of the geochemical effects of CO2 storage induced by the injection of CO2 into geologic reservoirs or by CO2 leakage into the overlaying formations can be performed by numerical modelling (non-invasive) and field experiments. Until now the research has been focused on the geochemical processes of the CO2 reacting with the minerals of the storage formation, which mostly consists of quartzitic sandstones. Regarding the safety assessment the reactions between the CO2 and the overlaying formations in the case of a CO2 leakage are of equal importance as the reactions in the storage formation. In particular, limestone formations can react very sensitively to CO2 intrusion. The thermodynamic parameters necessary to model these reactions are not determined explicitly through experiments at the total range of temperature and pressure conditions and are thus extrapolated by the simulation code. The differences in the calculated results lead to different calcite and CO2 solubilities and can influence the safety issues.This uncertainty study is performed by comparing the computed results, applying the geochemical modelling software codes The Geochemist’s Workbench, EQ3/6, PHREEQC and FactSage/ChemApp and their thermodynamic databases. The input parameters (1) total concentration of the solution, (2) temperature and (3) fugacity are varied within typical values for CO2 reservoirs, overlaying formations and close-to-surface aquifers. The most sensitive input parameter in the system H2O–CO2–NaCl–CaCO3 for the calculated range of dissolved calcite and CO2 is the fugacity of CO2. Hence, the largest range of dissolved calcite is calculated at high fugacities and is 210 mmol/kgw. The average deviation of the results using the databases phreeqc.dat and wateq4f.dat in combination with the code PHREEQC is lowest in comparison to the results of the specific model of Duan and Li, which represents the experimental values at best. Still, the solubility of CO2 is overestimated in the formation water using these two databases. Therefore, the model results calculate a larger retention capacity, defined as the quantity of CO2 dissolved in the formation water, than the Duan and Li model would do.  相似文献   

2.
Chemical interaction processes among injected CO2, saline fluids and potential reservoir materials are experimentally simulated to derive dissolution rates of natural materials (minerals) that can be used as input parameters for modeling of CO2 storage in deep saline formations and risk analyses. In order to study dissolution processes, mineral aliquots were exposed to CO2-bearing brines at elevated temperature (60, 100, 150 °C) and pressure (85 bar) and at various run durations. Several potential reservoir rocks include carbonates as cement. Calcite and dolomite grains were therefore mainly used as solid starting material. Experiments with the two feldspar varieties alkali feldspar and almost pure anorthite were performed in addition. Grain sizes of the mineral starting materials varied between <63 μm and 500 μm with most experiments performed at grain size fractions of 160 – 250 μm and 250 – 500 μm. All experiments run with a complex synthetic brine (total dissolved solids: ∼156 g/l) according to a natural upper cretaceous formation water. Dry ice was used as CO2-source. All experiments were done in closed batch reactors. These reactors allow mimicking reservoir conditions far from the injection site as well as reservoir conditions after finishing the CO2 injection. The concentration changes during the experiment were monitored by ICP-OES measurements of the initial and the post-run fluids. Dissolution rates were derived based on the concentration changes of the brine.Most of the studied experimental variables and parameters (temperature, run duration, grain size, brine composition – expressed as pH-value and ionic strength) impact alteration of the reacting agents, i.e. they change the chemical composition of the brine, change the surfaces of the mineral aliquots exposed to the CO2-bearing brine, and induce formation of secondary minerals. Hence, all influencing parameters on dissolution processes have to be considered and time-resolved changes of the dissolution behavior have to be implemented in numerical simulations of processes at CO2 injection sites and CO2 storage reservoirs.  相似文献   

3.
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.  相似文献   

4.
Among the risks of CO2 storage is the potential of CO2 leakage into overlaying formations and near-surface potable aquifers. Through a leakage, the CO2 can intrude into protected groundwater resources, which can lead to groundwater acidification followed by potential mobilisation of heavy metals and other trace metals through mineral dissolution or ion exchange processes. The prediction of pH buffer reactions in the formations overlaying a CO2 storage site is essential for assessing the impact of CO2 leakages in terms of trace metal mobilisation. For buffering the pH-value, calcite dissolution is one of the most important mechanisms. Although calcite dissolution has been studied for decades, experiments conducted under elevated CO2 partial pressures are rare. Here, the first study for column experiments is presented applying CO2 partial pressures from 6 to 43 bars and realising a near-natural flow regime. Geochemical calculations of calcite dissolution kinetics were conducted using PHREEQC together with different thermodynamic databases. Applying calcite surface areas, which were previously acquired by N2-BET or calculated based on grain diameters, respectively, to the rate laws according to Plummer et al. (Am J Sci 278:179–216, doi:10.2475/ajs.278.2.179, 1978) or Palandri and Kharaka (US Geol Surv Open file Rep 2004–1068:71, 2004) in the numerical simulations led to an overestimation of the calcite dissolution rate by up to three orders of magnitude compared to the results of the column experiments. Only reduction of the calcite surface area in the simulations as a fitting procedure allowed reproducing the experimental results. A reason may be that the diffusion boundary layer (DBL), which depends on the groundwater flow velocity and develops at the calcite grain surface separating it from the bulk of the solution, has to be regarded: The DBL leads to a decrease in the calcite dissolution rate under natural laminar flow conditions compared to turbulent mixing in traditional batch experiments. However, varying the rate constants by three orders of magnitudes in a field scale PHREEQC model simulating a CO2 leakage produced minor variations in the pH buffering through calcite dissolution. This justifies the use of equilibrium models when calculating the calcite dissolution in CO2 leakage scenarios for porous aquifers and slow or moderate groundwater flow velocities. However, the selection of the thermodynamic database has an impact on the dissolved calcium concentration, leading to an uncertainty in the simulation results. The resulting uncertainty, which applies also to the calculated propagation of an aquifer zone depleted in calcite through dissolution, seems negligible for shallow aquifers of approximately 60 m depth, but amounts to 35 % of the calcium concentration for aquifers at a depth of approximately 400 m.  相似文献   

5.
Surface coatings are very common on mineral grains in soils but most laboratory dissolution experiments are carried out on pristine, uncoated mineral grains. An experiment designed to unambiguously isolate the effect of surface coatings on mineral dissolution from any influence of solution saturation state is reported. Two aliquots of 53 to 63 μm anorthite feldspar powder were used. One was dissolved in pH 2.6 HCl, the other in pH 2.6 FeCl3 solution, both for ∼6000 h in flow-through reactors. An amorphous Fe-rich, Al-, Ca- and Si-free orange precipitate coated the anorthite dissolved in the FeCl3 solution. BET surface area of the anorthite increased from 0.16 to 1.65 m2 g−1 in the HCl experiment and to 3.89 m2 g−1 in the FeCl3 experiment. The increase in surface area in the HCl experiment was due to the formation of etch pits on the anorthite grain surface whilst the additional increase in the FeCl3 experiment was due to the micro- and meso-porous nature of the orange precipitate. This precipitate did not inhibit or slow the dissolution of the anorthite. Steady state dissolution rates for the anorthite dissolved in the HCl and FeCl3 were ∼2.5 and 3.2 × 10−10 molfeldspar m−2 s−1 respectively. These rates are not significantly different after the cumulative uncertainty of 17% in their value due to uncertainty in the inputs parameters used in their calculation is taken into account. Results from this experiment support previous theoretical and inference-based conclusions that porous coatings should not inhibit mineral dissolution.  相似文献   

6.
Anthropogenic carbon dioxide (CO2) emissions reduce pH of marine waters due to the absorption of atmospheric CO2 and formation of carbonic acid. Estuarine waters are more susceptible to acidification because they are subject to multiple acid sources and are less buffered than marine waters. Consequently, estuarine shell forming species may experience acidification sooner than marine species although the tolerance of estuarine calcifiers to pH changes is poorly understood. We analyzed 23 years of Chesapeake Bay water quality monitoring data and found that daytime average pH significantly decreased across polyhaline waters although pH has not significantly changed across mesohaline waters. In some tributaries that once supported large oyster populations, pH is increasing. Current average conditions within some tributaries however correspond to values that we found in laboratory studies to reduce oyster biocalcification rates or resulted in net shell dissolution. Calcification rates of juvenile eastern oysters, Crassostrea virginica, were measured in laboratory studies in a three-way factorial design with 3 pH levels, two salinities, and two temperatures. Biocalcification declined significantly with a reduction of ∼0.5 pH units and higher temperature and salinity mitigated the decrease in biocalcification.  相似文献   

7.
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.  相似文献   

8.
Convective mixing of dissolved carbon dioxide (CO2) with formation brine has been shown to be a significant factor for the rate of dissolution of CO2 and thus for determining the viability of geological CO2 storage sites. In most previous convection investigations, a no-flow boundary condition was used to represent the interface between an upper region with CO2 and brine and the single-phase brine region beneath. However, due to interfacial tension between the phases, the water phase is partly mobile in the upper region and advection may occur. Based on linear stability analysis and numerical simulations, we show that advection across the interface leads to considerable destabilization of the system. In particular, the time of onset of instability is reduced by a factor of two and the rate of dissolution is enhanced by a factor of two for three of four formations we consider, and by 40 % for the fourth formation. It is found that exponential decay of the relative permeability away from the interface provides a useful approximation to the real system. In addition, the exponential decay also simplifies the linear stability analysis. Interestingly, formations with large absolute permeability and small porosity have the largest impact from the transition zone, despite the fact that the relative permeability decays quickly above the interface in these formations. This is because the length-scale of instability is smallest in these formations.  相似文献   

9.
A benchmark study on problems related to CO2 storage in geologic formations   总被引：1，自引：0，他引：1  
  相似文献   

10.
In order to evaluate the extent of CO2–water–rock interactions in geological formations for C sequestration, three batch experiments were conducted on alkali feldspars–CO2–brine interactions at 150–200 °C and 300 bars. The elevated temperatures were necessary to accelerate the reactions to facilitate attainable laboratory measurements. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. SEM, TEM and XRD analysis of reaction products showed extensive dissolution features (etch pits, channels, kinks and steps) on feldspars and precipitation of secondary minerals (boehmite, kaolinite, muscovite and paragonite) on feldspar surfaces. Therefore, these experiments have generated both solution chemistry and secondary mineral identity. The experimental results show that partial equilibrium was not attained between secondary minerals and aqueous solutions for the feldspar hydrolysis batch systems. Evidence came from both solution chemistry (supersaturation of the secondary minerals during the entire experimental duration) and metastable co-existence of secondary minerals. The slow precipitation of secondary minerals results in a negative feedback in the dissolution–precipitation loop, reducing the overall feldspar dissolution rates by orders of magnitude. Furthermore, the experimental data indicate the form of rate laws greatly influence the steady state rates under which feldspar dissolution took place. Negligence of both the mitigating effects of secondary mineral precipitation and the sigmoidal shape of rate–ΔGr relationship can overestimate the extent of feldspar dissolution during CO2 storage. Finally, the literature on feldspar dissolution in CO2-charged systems has been reviewed. The data available are insufficient and new experiments are urgently needed to establish a database on feldspar dissolution mechanism, rates and rate laws, as well as secondary mineral information at CO2 storage conditions.  相似文献   

11.
《Applied Geochemistry》2005,20(6):1131-1157
The Weyburn Oil Field is a carbonate reservoir in south central Saskatchewan, Canada and is the site of a large CO2 injection project for purposes of enhanced oil recovery. The Weyburn Field, in the Mississippian Midale Formation, was discovered in 1954 and was under primary production until secondary recovery by water flood began in 1964. The reservoir comprises two units, the Vuggy and the Marly, and primary and secondary recovery are thought to only have significantly depleted the Vuggy zone, leaving the Marly with higher oil saturations. In 2000, PanCanadian Resources (now EnCana), the operator of the field, began tertiary recovery by injection of CO2 and water, primarily into the Marly. The advent of this project was an opportunity to study the potential for geological storage of CO2.Using 43 Baseline samples collected in August 2000, before CO2 injection at Weyburn, and 44 monitoring samples collected in March 2001, changes in the fluid chemistry and isotope composition have been tracked. The initial fluid distribution showed water from discovery through water flood in the Midale Formation with Cl ranging from 25,000 to 60,000 mg/L, from the NW to the SE across the Phase 1A area. By the time of Baseline sampling the produced water had been diluted to Cl of 25,000–50,000 mg/L as a result of the addition of make up water from the low TDS Blairmore Formation, but the pattern of distribution was still present. The Cl distribution is mimicked by the distribution of other dissolved ions and variables, with Ca (1250–1500 mg/L) and NH3 (aq) increasing from NW to SE, and alkalinity (700–300 mg/L), resistivity, and H2S (300–100 mg/L) decreasing. Based on chemical and isotopic data, the H2S is interpreted to result from bacterial SO4 reduction. After 6 months of injection of CO2, the general patterns are changed very little, except that the pH has decreased by 0.5 units and alkalinity has increased, with values over 1400 mg/L in the NW, decreasing to 500 mg/L in the SE. Calcium has increased to range from 1250 to 1750 mg/L, but the pattern of NW–SE distribution is altered. Chemical and isotopic data suggest this change in distribution is caused by the dissolution of calcite due to water–rock reactions driven by CO2. The Baseline samples varied from −22 to −12‰ δ13C (V-PDB) for CO2 gas. The injected CO2 has an isotope ratio of −20‰. The Monitor-1 samples of produced CO2 ranged from −18 to −13‰, requiring a heavy source of C, most easily attributed to dissolution of carbonate minerals. Field measured pH had increased and alkalinity had decreased by the second monitoring trip (July 2001) to near Baseline values, suggesting continued reaction with reservoir minerals.Addition of CO2 to water–rock mixtures comprising carbonate minerals causes dissolution of carbonates and production of alkalinity. Geochemical modeling suggests dissolution is taking place, however more detail on water–oil–gas ratios needs to be gathered to obtain more accurate estimates of pH at the formation level. Geological storage of CO2 relies on the potential that, over the longer term, silicate minerals will buffer the pH, causing any added CO2 to be precipitated as calcite. Some initial modeling of water–rock reactions suggests that silica sources are available to the water resident in the Midale Formation, and that clay minerals may well be capable of acting as pH buffers, allowing injected CO2 to be stored as carbonate minerals. Further work is underway to document the mineralogy of the Midale Formation and associated units so as to define more accurately the potential for geological storage.  相似文献   

12.
Increasing attention is being focused on the rapid rise of CO2 levels in the atmosphere, which many believe to be the major contributing factor to global climate change. Sequestering CO2 in deep geological formations has been proposed as a long-term solution to help stabilize CO2 levels. However, before such technology can be developed and implemented, a basic understanding of H2O–CO2 systems and the chemical interactions of these fluids with the host formation must be obtained. Important issues concerning mineral stability, reaction rates, and carbonate formation are all controlled or at least significantly impacted by the kinetics of rock–water reactions in mildly acidic, CO2-saturated solutions. Basalt has recently been identified as a potentially important host formation for geological sequestration. Dissolution kinetics of the Columbia River Basalt (CRB) were measured for a range of temperatures (25–90 °C) under mildly acidic to neutral pH conditions using the single-pass flow-through test method. Under anaerobic conditions, the normalized dissolution rates for CRB decrease with increasing pH (3 ? pH ? 7) with a slope, η, of −0.15 ± 0.01. Activation energy, Ea, has been estimated at 32.0 ± 2.4 kJ mol−1. Dissolution kinetics measurements like these are essential for modeling the rate at which CO2-saturated fluids react with basalt and ultimately drive conversion rates to carbonate minerals in situ.  相似文献   

13.
Due to the poor preservation of old peat formations and the limited research developed on them, the contribution of peat oxidation to the global C cycle at geological scales is poorly understood. Iron duricrusts containing abundant well-preserved plant structures have been reported above Humic Gleysols in the Uberaba Plateau (Brazil). We show that the iron accumulation results from an in-situ impregnation of peat, fast enough to preserve the plant structures. The formation of iron oxides results from two processes: precipitation in the pores and C/Fe replacement. The iron duricrusts were probably triggered by oxidation of the peatland following dry climatic events during the last 50 kyr. The large amount of iron dissolved in peatland waters was immobilized contemporaneously with the destruction of organic matter. The oxidation of organic matter from the lower peat, dated at ca 24–27 kyr BP, may have released between 0.08 and 2.26 kg CO2 m−2 yr−1 in the atmosphere. These rates are in a good agreement with present-day measurements of CO2 release from drained peatlands. Although peatland formation has been identified as a significant contributor to the global CO2 uptake, our findings suggest that natural peatland oxidation should also be considered as a source of atmospheric CO2 during past climate change.  相似文献   

14.
The Johansen formation is a candidate site for large-scale CO2 storage offshore of the south-western coast of Norway. An overview of the geology for the Johansen formation and neighboring geological formations is given, together with a discussion of issues for geological and geophysical modelling and integrated fluid flow modelling. We further describe corresponding simulation models. Major issues to consider are capacity estimation and processes that could potentially cause CO2 to leak out of the Johansen formation and into the formations above. Currently, these issues can only be investigated through numerical simulation. We consider the effect of different boundary conditions, sensitivity with respect to vertical grid refinement and permeability/transmisibility data, and the effect of residual gas saturations, since these strongly affect the CO2-plume distribution. The geological study of the Johansen formation is performed based on available seismic and well data. Fluid simulations are performed using a commercial simulator capable of modelling CO2 flow and transport by simple manipulation of input files and data. We provide details for the data and the model, with a particular focus on geology and geometry for the Johansen formation. The data set is made available for download online.  相似文献   

15.
Capturing CO2 from point sources and storing it in geologic formations is a potential option for allaying the CO2 level in the atmosphere. In order to evaluate the effect of geological storage of CO2 on rock-water interaction, batch experiments were performed on sandstone samples taken from the Altmark reservoir, Germany, under in situ conditions of 125 °C and 50 bar CO2 partial pressure. Two sets of experiments were performed on pulverized sample material placed inside a closed batch reactor in (a) CO2 saturated and (b) CO2 free environment for 5, 9 and 14 days. A 3M NaCl brine was used in both cases to mimic the reservoir formation water. For the “CO2 free” environment, Ar was used as a pressure medium. The sandstone was mainly composed of quartz, feldspars, anhydrite, calcite, illite and chlorite minerals. Chemical analyses of the liquid phase suggested dissolution of both calcite and anhydrite in both cases. However, dissolution of calcite was more pronounced in the presence of CO2. In addition, the presence of CO2 enhanced dissolution of feldspar minerals. Solid phase analysis by X-ray diffraction and Mössbauer spectroscopy did not show any secondary mineral precipitation. Moreover, Mössbauer analysis did not show any evidence of significant changes in redox conditions. Calculations of total dissolved solids’ concentrations indicated that the extent of mineral dissolution was enhanced by a factor of approximately 1.5 during the injection of CO2, which might improve the injectivity and storage capacity of the targeted reservoir. The experimental data provide a basis for numerical simulations to evaluate the effect of injected CO2 on long-term geochemical alteration at reservoir scale.  相似文献   

16.
《Applied Geochemistry》2004,19(8):1217-1232
Laboratory experiments were conducted with volcanic ash soils from Mammoth Mountain, California to examine the dependence of soil dissolution rates on pH and CO2 (in batch experiments) and on oxalate (in flow-through experiments). In all experiments, an initial period of rapid dissolution was observed followed by steady-state dissolution. A decrease in the specific surface area of the soil samples, ranging from 50% to 80%, was observed; this decrease occurred during the period of rapid, initial dissolution. Steady-state dissolution rates, normalized to specific surface areas determined at the conclusion of the batch experiments, ranged from 0.03 μmol Si m−2 h−1 at pH 2.78 in the batch experiments to 0.009 μmol Si m−2 h−1 at pH 4 in the flow-through experiments. Over the pH range of 2.78–4.0, the dissolution rates exhibited a fractional order dependence on pH of 0.47 for rates determined from H+ consumption data and 0.27 for rates determined from Si release data. Experiments at ambient and 1 atm CO2 demonstrated that dissolution rates were independent of CO2 within experimental error at both pH 2.78 and 4.0. Dissolution at pH 4.0 was enhanced by addition of 1 mM oxalate. These observations provide insight into how the rates of soil weathering may be changing in areas on the flanks of Mammoth Mountain where concentrations of soil CO2 have been elevated over the last decade. This release of magmatic CO2 has depressed the soil pH and killed all vegetation (thus possibly changing the organic acid composition). These indirect effects of CO2 may be enhancing the weathering of these volcanic ash soils but a strong direct effect of CO2 can be excluded.  相似文献   

17.
One of the uncertainties in the field of carbon dioxide capture and storage (CCS) is caused by the parameterization of geochemical models. The application of geochemical models contributes significantly to calculate the fate of the CO2 after its injection. The choice of the thermodynamic database used, the selection of the secondary mineral assemblage as well as the option to calculate pressure dependent equilibrium constants influence the CO2 trapping potential and trapping mechanism. Scenario analyses were conducted applying a geochemical batch equilibrium model for a virtual CO2 injection into a saline Keuper aquifer. The amount of CO2 which could be trapped in the formation water and in the form of carbonates was calculated using the model code PHREEQC. Thereby, four thermodynamic datasets were used to calculate the thermodynamic equilibria. Furthermore, the equilibrium constants were re-calculated with the code SUPCRT92, which also applied a pressure correction to the equilibrium constants. Varying the thermodynamic database caused a range of 61% in the amount of trapped CO2 calculated. Simultaneously, the assemblage of secondary minerals was varied, and the potential secondary minerals dawsonite and K-mica were included in several scenarios. The selection of the secondary mineral assemblage caused a range of 74% in the calculated amount of trapped CO2. Correcting the equilibrium constants with respect to a pressure of 125 bars had an influence of 11% on the amount of trapped CO2. This illustrates the need for incorporating sensitivity analyses into reaction pathway modeling.  相似文献   

18.
Iron mobilisation from aquifer rocks in an important fractured aquifer system in South Africa is resulting in clogging of boreholes by Fe oxide minerals. Leach experiments using natural waters were conducted to determine the effects of redox conditions, pH lithology and presence of organic acids on the rate and extent of Fe dissolution from aquifer rocks, with the aim of clarifying the association of Fe clogging with geological formations that show Fe staining on weathering. The results indicate that the greatest amount of Fe (>30 mmol/kg rock) is leached from arenaceous rocks with low total Fe contents (49.0–75.0 mmol/kg) under anoxic conditions. Rocks with the highest Fe contents (>800 mmol/kg) generated low concentrations of Fe (<10 mmol/kg) even under favourable conditions of 0 mg/L DO and pH 3. The extent of Fe dissolution from the rocks was found to be most strongly dependent on the redox conditions, and the form of Fe present in the rock, with ascorbate-extracted amorphous Fe being the most mobile. The rate of dissolution is affected by pH and the presence of natural organic acids in the leachate. However, the effect of organic acids was only noticeable on arenaceous rocks.  相似文献   

19.
The assessment of the environmental impacts of CO2 geological storage requires the investigation of potential CO2 leakages into fresh groundwater, particularly with respect to protected groundwater resources. The geochemical processes and perturbations associated with a CO2 leak into fresh groundwater could alter groundwater quality: indeed, some of the reacting minerals may contain hazardous constituents, which might be released into groundwater. Since the geochemical reactions may occult direct evidence of intruding CO2, it is necessary to characterize these processes and identify possible indirect indicators for monitoring CO2 intrusion. The present study focuses on open questions: Can changes in water quality provide evidence of CO2 leakage? Which parameters can be used to assess impact on freshwater aquifers? What is the time scale of water chemistry degradation in the presence of CO2? The results of an experimental approach allow selecting pertinent isotope tracers as possible indirect indicators of CO2 presence, opening the way to devise an isotopic tracing tool.The study area is located in the Paris Basin (France), which contains deep saline formations identified as targets by French national programs for CO2 geological storage. The study focuses on the multi-layered Albian fresh water aquifer, confined in the central part of the Paris Basin a major strategic potable groundwater overlying the potential CO2 storage formations. An experimental approach (batch reactors) was carried out in order to better understand the rock–water–CO2 interactions with two main objectives. The first was to assess the evolution of the formation water chemistry and mineralogy of the solid phase over time during the interaction. The second concerned the design of an isotopic monitoring program for freshwater resources potentially affected by CO2 leakage. The main focus was to select suitable environmental isotope tracers to track water rock interaction associated with small quantities of CO2 leaking into freshwater aquifers.In order to improve knowledge on the Albian aquifer, and to provide representative samples for the experiments, solid and fluid sampling campaigns were performed throughout the Paris Basin. Albian groundwater is anoxic with high concentrations of Fe, a pH around 7 and a mineral content of 0.3 g L−1. Macroscopic and microscopic solid analyses showed a quartz-rich sand with the presence of illite/smectite, microcline, apatite and glauconite. A water–mineral–CO2 interaction batch experiment was used to investigate the geochemical evolution of the groundwater and the potential release of hazardous trace elements. It was complemented by a multi-isotope approach including δ13CDIC and 87Sr/86Sr. Here the evolution of the concentrations of major and trace elements and isotopic ratios over batch durations from 1 day to 1 month are discussed. Three types of ion behavior are observed: Type I features Ca, SiO2, HCO3, F, PO4, Na, Al, B, Co, K, Li, Mg, Mn, Ni, Pb, Sr, Zn which increased after initial CO2 influx. Type II comprises Be and Fe declining at the start of CO2 injection. Then, type III groups element with no variation during the experiments like Cl and SO4. The results of the multi-isotope approach show significant changes in isotopic ratios with time. The contribution of isotope and chemical data helps in understanding geochemical processes involved in the system. The isotopic systems used in this study are potential indirect indicators of CO2–water–rock interaction and could serve as monitoring tools of CO2 leakage into an aquifer overlying deep saline formations used for C sequestration and storage.  相似文献   

20.
Documenting geographic distribution and spatial linkages between CO2 sources and potential sinks in areas with significant levels of CO2 emissions is important when considering carbon-management strategies such as geologic sequestration or enhanced oil recovery (EOR). For example, the US Gulf Coast overlies a thick succession (>6,000 m [>20,000 ft]) of highly porous and permeable sandstone formations separated by thick, regionally extensive shale aquitards. The Gulf Coast and Permian Basin also have a large potential for EOR, in which CO2 injected into suitable oil reservoirs could be followed by long-term storage of CO2 in nonproductive formations below reservoir intervals. For example, >6 billion barrels (Bbbl) of oil from 182 large reservoirs is technically recoverable in the Permian Basin as a result of miscible-CO2 flooding. The Gulf Coast also contains an additional 4.5 Bbbl of oil that could be produced by using miscible CO2. Although the CO2 pipeline infrastructure is well-developed in the Permian Basin, east Texas and the Texas Gulf Coast may have a greater long-term potential for deep, permanent storage of CO2 because of thick brine-bearing formations near both major subsurface and point sources of CO2.  相似文献   

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