Fate Of CO2 Research Articles

Controls of sluggish, CO2-promoted, hematite and K-feldspar dissolution kinetics in sandstones

CO2 sequestration is regarded as an important strategy for reducing anthropogenic CO2 emissions. Both the nature and rate of fluid–mineral reactions in CO2–water–rock systems are crucial, yet poorly constrained, parameters in understanding the fate of CO2 injected in geological formations. This study models reactions and reaction rates in an exhumed CO2-charged aquifer where CO2-rich brines have bleached red sandstones by dissolution of hematite grain coatings. We show that the vertical movement of the reaction front is dominated by diffusion and this allows calculation of reaction rates for the dissolution of hematite grain coatings and K-feldspar. Using mineral surface areas calculated from BET measurements, we estimate K-feldspar dissolution rates of 3.4±2.0×10−13molm−2s−1; and hematite reaction rates of 6.1±5.0×10−16molm−2s−1. The rates for K-feldspar are lower than previous, experimentally derived, estimates of K-feldspar dissolution rates by 1–2 orders of magnitude, likely explained by the proximity of the natural system to equilibrium. The inferred hematite reaction rates are 5–6 orders of magnitude slower than laboratory experiments and appear to be controlled by the chemical gradients imposed by the more sluggish K-feldspar dissolution. As the majority of potentially mobile trace metals are hosted in iron-oxide grain coatings, we argue that the rate of contaminant mobilization by CO2-charged brines will be lower than suggested by laboratory experiments.

Microbial community structure and microbial activities related to CO2 storage capacities of a salt cavern

Salt caverns are cavities that form in salt deposits and can be used for hydrocarbon or gas storage as well as waste disposal. Despite high salt concentrations in those environments, microbial life still occurs and affects the storage or disposal capacities of the cavern. In order to predict what may occur over time it is important to understand the types of microorganisms present in salt caverns and the environmental impact of their activities. For example if salt caverns were to be used for CO2 storage, the fate of CO2 will be impacted by microbial activities. In the presence of H2 microorganisms can convert CO2 to acetic acid and water or to methane and water. Samples from a salt cavern plant used to store oily sand were obtained and used to determine microbial community composition by pyrosequencing. Community analyses showed a halophilic, thermophilic community including the genera Methanohalophilus, Methanolobus and others capable of producing methane. Oil-degrading genera (Halanaerobium and Marinobacter), sulfate-reducing genera (Desulfovermiculus and Desulfovibrio) as well as the genus Acetohalobium capable of producing acetic acid in high salt environments were also prevalent. Determination of microbial activities related to CO2 fixation or transformation (homoacetogenic activity and hydrogenotrophic methanogenic activity) indicated that the salt caverns have homoacetogenic activity at both high and low salt concentration. Methanogenic activity was observed with low salt concentration only. Thus if salt caverns were to be used for CO2 storage production of acetic acid, but not of methane, is expected if H2 is present.

Forsterite Dissolution in Saline Water at Elevated Temperature and High CO2 Pressure

The rates and mechanisms of magnesium silicate dissolution can control the aqueous chemistry in ways that influence carbonate mineral precipitation during geologic carbon sequestration (GCS). A series of batch experiments was performed with forsterite (Mg(1.81)Fe(0.19)SiO(4)) powder to determine the effects of pressure (10-100 bar CO(2)), temperature (25-100 °C), and salinity (0-50,000 mg/L NaCl) on its dissolution rate at conditions relevant to GCS. Dissolution rates and products were determined by analysis of the aqueous phase, equilibrium and reaction path modeling, and solid phase characterization by scanning electron microscopy and X-ray diffraction. After an initially rapid dissolution period, the dissolution rate declined significantly, an effect that is attributed to the formation of a silica-rich layer at the forsterite surface. The initial dissolution rate increased with increasing temperature and increasing CO(2) pressure; the effect of CO(2) was through its influence on the pH. The dissolution rate was enhanced by NaCl, which may have been due to its inhibition of the formation of a silica-rich surface layer. The experimental results provide information about magnesium silicate dissolution at conditions that will be encountered during GCS that can be used to predict the fate of CO(2) and the evolution of subsurface geochemistry following CO(2) injection.

Stable carbon isotope techniques to quantify CO2 trapping under pre-equilibrium conditions and elevated pressures and temperatures

Flow-through experiments in the laboratory were conducted to monitor the fate of CO2 using stable carbon isotope (δ13C) techniques in dynamic, pre-equilibrium conditions. Such conditions are typical, for instance in carbon capture storage (CCS), in the initial stages of CO2 injection, near injection well regions of the reservoir. For this purpose, a reactive percolation bench (ICARE 4) was used, injecting a CO2-saturated brine at supercritical conditions (pCO2=84bar, T=60°C) through quartzitic limestone at an average flow rate of 2×10−9m3s−1. Calcium (Ca2+) and dissolved inorganic carbon (DIC) concentration data and pH were used to aid analytical interpretations. During CO2 injection, δ13CDIC values decreased from about −11‰ to those of the injected CO2 (−29.3‰), indicating CO2 sourced carbon dominance over a carbonate sourced one in the system. Simultaneously DIC and Ca2+ concentrations increased from 1mmolL−1 to a maximum of 71mmolL−1 and 31mmolL−1, respectively. Isotope and mass balances were used to quantify the amount of DIC originating from either the injected CO2 or carbonates. At the end of the experiments, between 70 and 98% of the total DIC originated from CO2 dissolution, the remaining amount is attributed to carbonate dissolution. Furthermore, the total amount of injected CCO2 trapped as DIC ranged between 9 and 17% and between 83 and 91% was in free phase. The state of carbonate equilibrium of the host fluid, under the high pressure–temperature conditions after CO2 injection was identified, verifying pre-equilibrium conditions. Results confirm observations made in reported field data. This emphasises that the combination of CO2 monitoring, the development of a thorough understanding of carbonate equilibrium, as well as the quantification of CO2-trapping, is essential for a solid assessment of reservoir performance and safety considerations during CO2 injection. These are equally important for understanding water–rock–CO2 dynamics in natural subsurface environments.

Preliminary results of the Slovakian national project regarding carbon dioxide storage in underground spaces

Abstract The Slovak republic territory in spite of its extremely complicated geological pattern affords some possibilities for potential storage of carbon dioxide. The aim of the Slovakian National project “Quantitative parameters selected geological structures suitable for CO 2 storage” is to find convenient places for this purpose in regional aquifers, and depleted hydrocarbon deposits. Besides, of these geological rock complexes–mostly ultramafic rocks - have been investigated for purposes of mineral carbonation of CO 2 . The first attempt about fate of CO 2 in brine (regional aquifer) has been modelled from geochemical point of view.. From the preliminary results of the all above - mentioned options is obvious that for the process of the practical activation of CCS technologies many collisions with hydrogeological, geothermal and land use planning activities and regulations will be necessary to solve.

Northwest McGregor field CO2 Huff ‘n’ Puff: A case study of the application of field monitoring and modeling techniques for CO2 prediction and accounting

Northwest McGregor field CO2 Huff ‘n’ Puff: A case study of the application of field monitoring and modeling techniques for CO2 prediction and accounting

CO2 injection in Buracica — Long-term performance assessment

Abstract The purpose of this study is to apply the performance assessment process, using the experimental design theory and the response surface methodology, to the Buracica field in order to evaluate the suitability level of the method for establishing the practicability of CO2 geological storage. The work reported here concerns the modelling of the CO2 behaviour within the reservoir and its burdens over the next 1,000 years without taking into account the possible geochemical and geomechanical impact. The first step of this study was to simulate the CO2 injection phase using a compositional model. The second step consisted in establishing future risk scenarios which represent the possible flow and fate of CO2. They concern damaged wells, the cap rock features and the North fault conductivity.

Field-case simulation of CO2 -plume migration using vertical-equilibrium models

When injected in deep saline aquifers, CO2 moves radially away from the injection well and progressively higher in the formation because of buoyancy forces. Analyzes have shown that after the injection period, CO2 will potentially migrate over several kilometers in the horizontal direction but only tens of meters in the vertical direction, limited by the aquifer caprock [1, 2]. Because of the large horizontal plume dimensions, three-dimensional numerical simulations of the plume migration over long periods of time are computationally intensive. Thus, to get results within a reasonable time frame, one is typically forced to use coarse meshes and long time steps which result in inaccurate results because of numerical errors in resolving the plume tip. Given the large aspect ratio between the vertical and horizontal plume dimensions, it is reasonable to approximate the CO2 migration using vertically averaged models. Such models can, in many cases, be more accurate than coarse three-dimensional computations. In particular, models based on vertical equilibrium (VE) [3] are attractive to simulate the long-term fate of CO2 sequestered into deep saline aquifers. The reduced spatial dimensionality resulting from the vertical integration ensures that the computational performance of VE models exceeds the performance of standard three-dimensional models. Thus, VE models are suitable to study the long-time and large-scale behavior of plumes in real large-scale CO2-injection projects [4, 1, 2, 5]. We investigate the use of VE models to simulate CO2 migration in a real large-scale eld case based on data from the Sleipner site in the North Sea. We discuss the potential and limitations of VE models and show how VE models can be used to give reliable estimates of long-term CO2 migration. In particular, we focus on a VE formulation that incorporates the aquifer geometry and heterogeneity, and that considers the eects of hydrodynamic and residual trapping. We compare the results of VE simulations with standard reservoir simulation tools on test cases and discuss their advantages and limitations and show how, provided that certain conditions are met, they can be used to give reliable estimates of long-term CO2 migration.

TOUGHREACT modeling of the fate of CO2 injected into a H2S containing saline aquifer: The example of the Wabamum Area Sequestration Project (WASP)

Abstract The Devonian Nisku formation in central Alberta is potentially a suitable aquifer for CO2 sequestration. As with many Devonian aged aquifers in the Western Canada Sedimentary Basin, it contains H2S from thermochemical sulfate reduction. In spite of this, the Devonian Nisku represents a potentially desirable location as it is at the correct depth to ensure that CO2 is in the supercritical phase, it has multiple impermeable and low permeability barriers and there is very little hydrocarbon production in the formation. This paper presents a modeling study of the injection phase of CO2 into a saline aquifer in the Devonian Nisku formation at Wabamum Lake in Central Alberta. The object of the study is to evaluate the differences and problems, if any, between injection into a brine with an ambient amount of dissolved H2S and without dissolved H2S. The simulation covers a CO2 injection period of 50 years at a rate of 1 Mt/year. A one dimensional, radial symmetric model was used with a uniform carbonate composition. The mineral composition was from the Upper Nisku formation and a water composition from a producing water well in the Nisku formation. The model found that injected CO2 was stored as ionically trapped bicarbonate in a region of varying widths, 300 m wide after 1 year of injection to 3000 m wide after 50 years of injection represents from 2% to 3% of injected CO2. Small amounts are also trapped as calcite and dolomite. The H2S in solution does exsolve as gas during injection but this result is inconclusive due to the small amount of dissolved H2S present in the ambient brine. Overall, there were no noticeable differences between the models with and without ambient H2S in the brine.

CO2 -porewater-rock reactions–Large-scale column experiment (Big Rig II)

This study focused on the reactions between carbon dioxide (CO2), porewater and host rock during geological CO2 storage in deep reservoirs. The aim of this work was to provide a well-constrained laboratory experiment reacting known quantities of minerals with CO2-rich fluids, to simulate situations where CO2 is being injected into lithologies deep underground. The experiment was undertaken using a Ti-column, 100 cm long, held within a large pressure vessel. The column was packed with a simplified mineral assemblage. The reactant fluid was equilibrated with CO2 at a temperature of 130 °C and a pressure of 300 bar, before being pumped into the column held under the same conditions. Fluid was passed along the column at a constant flow rate for approximately 3.5 months. Fluids collected from the outlet end of the column were analysed to provide data on the fate of the dissolved species. On completion of the experiment, the column was then examined for mineralogical changes. The experimental results can be used as a test case for predictive geochemical computer modelling. Such models will help improve our ability to predict the long-term fate of CO2 stored underground.

Coupled reactive flow and transport modeling of CO 2 sequestration in the Mt. Simon sandstone formation, Midwest U.S.A.

Multi-phase reactive flow and transport modeling is an effective tool for monitoring, verification, and accounting of CO 2 sequestration in deep geological formations. In the current study, modeling is performed to simulate large scale CO 2 injection (a million tons per year for 100 years) into Mt. Simon sandstone, a major candidate saline reservoir in the Midwest of USA. The long term fate of CO 2 was simulated by extending the modeling period to 10,000 years. The results indicate that most of the injected CO 2 remains within a radius of 3300 m lateral distribution. Four major trapping mechanisms and their spatial and temporal variations are evaluated in our simulations: hydrodynamic, solubility, residual, and mineral trapping. A strongly acidified zone (pH 3–5) forms in the areas affected by the injected CO 2 (0–3300 m), and consequently causes extensive mineral precipitation and dissolution. The predicted long-term fate of CO 2 is closely linked to the geochemical reactions conceptualized in the models. In our model, the replenishing upstream water continues to dissolve CO 2 long after the injection, which results in total dissolution of hydrodynamically trapped CO 2 at the end of 10,000 years. In contrast, most previous models neglected the regional flow after injection and hence artificially limited the extent of geochemical reactions as if in a batch system. Consequently, a supercritical CO 2 plume (hydrodynamic trapping) would persist after 10,000 years. The continued supply of acidified water from interaction between replenishing water and CO 2 also results in extensive dissolution of feldspars and precipitation of secondary clay minerals, to a much more extent than what predicted in models without including regional flow. However, the prediction of complete dissolution of feldspars in 10,000 years can also result from the artifact that the linear rate laws are used in our model (as well as all previous work), which overestimates the rates of feldspar dissolution near equilibrium. Nevertheless, our simulations indicate the prolonged existence of an acidic brine plume, which suggests long-term risk assessment should transfer from the primary risk of CO 2 leakage to secondary risk of acidic plume leakage after all CO 2 is dissolved.

Carbonate cements in Miller field of the UK North Sea: a natural analog for mineral trapping in CO2 geological storage

Miller field of the North Sea has had high concentrations of natural CO2 for ~70 Ma. It is an ideal analog for the long-term fate of CO2 during engineered storage, particularly for formation of carbonate minerals that permanently lock up CO2 in solid form. The Brae Formation reservoir sandstone contains an unusually high quantity of calcite concretions; however, C and O stable isotopic signatures suggest that these are not related to the present-day CO2 charge. Margins of the concretions are corroded, probably because of reduced pH due to CO2 influx. Dispersed calcite cements are also present, some of which postdate the CO2 charge and, therefore, are the products of mineral trapping. It is calculated that only a minority of the reservoired CO2 in Miller (6–24%) has been sequestrated in carbonates, even after 70 Ma of CO2 emplacement. Most of the CO2 accumulation is dissolved in pore fluids. Therefore, in a reservoir similar to the Brae Formation, engineered CO2 storage must rely on physical retention mechanisms because mineral trapping is both incomplete and slow.

Investigation of the binding of Cr(III) complexes to bovine and human serum proteins: A proteomic approach

Chromium (Cr) compounds are widely used in alloys manufacturing and forming processes. One of the main concerns in the use of cobalt-chromium (Co-Cr) alloy-based implants is the long-term fate of Co and Cr ions in the blood, organs, and urine of patients. Our previous studies have shown that Cr(III) forms complexes in different cell culture media, whereas Cr(VI) does not form any detectable structure under the same conditions. Because Cr(VI) is known to be more toxic than Cr(III), we hypothesized that the presence of serum proteins in the molecular structure of Cr(III) may be responsible for the difference in toxicity. We investigated the interaction of the Cr(III) complexes with serum proteins and their internalization by U937 macrophage-like cells. By using a proteomic approach, we showed that in the presence of fetal bovine serum, Cr(III) complexes interacted only with albumin, whereas they interacted mainly with albumin, transferrin, and immunoglobulins (Ig) in the presence of human serum (HS). Cr(III) complexes were more easily engulfed by U937 macrophage-like cells when they were formed with HS. To the best of our knowledge, this is the first report on the formation of Cr(III) complexes in the presence of serum proteins and the interaction of these complexes with U937 macrophage-like cells. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

The rock physics basis for 4D seismic monitoring of CO2 fate: Are we there yet?

Monitoring, verification, and accounting (MVA) of [Formula: see text] fate are three fundamental needs in geological sequestration. The primary objective of MVA protocols is to identify and quantify (1) the injected [Formula: see text] stream within the injection/storage horizon and (2) any leakage of sequestered gas from the injection horizon, providing public assurance. Thus, the success of MVA protocols based on seismic prospecting depends on having robust methodologies for detecting the amount of change in the elastic rock property, assessing the repeatability of measured changes, and interpreting and analyzing the detected changes to make quantitative predictions of the movement, presence, and permanence of [Formula: see text] storage, including leakage from the intended storage location.

Micro/Nanotransport Phenomena in Renewable Energy and Energy Efficiency

This article introduces a series of papers presented in a special issue entitled: “Micro/Nanotransport Phenomena in Renewable Energy and Energy Efficiency.” The papers in this issue address some of the basic aspects of renewable energy harvest/conversion, emission control, and optimization of energy. The first article describes a new method based on Femtosecond laser that can be used to fabricate high-quality metallic light absorbers. These artificially made surfaces can be used to improve the energy conversion efficiency such as thermophotovoltaics and solar energy absorbers. Articles on fuel cells cover the experimental and numerical study of cold startup of Proton Exchange Membrane (PEM) fuel cell, development of a continuum model for water transport in the Ionomer-phase of catalyst-coated membranes for PEM, and mesoscopic modeling based on the lattice Boltzmann method for water management in fuel cells. In the area of emission control, the next article discuss the use of nanosized cerium oxide particles as additives on biodiesel, reporting that these additives can appreciably reduce the emission levels of hydrocarbon and NOx through enhancing hydrocarbon oxidation and promoting complete combustion. Another article found that mesoscopic modeling of multiphysicochemical transport phenomena in porous media based on the lattice Boltzmann method (LBM) is especially effective to model the dissolving process of supercritical CO2 into geologic formations such as limestone rock. This may provide a comprehensive numerical tool to simulate the long-term fate of CO2 after injection into the geologic formations. Additional articles discuss thermal management and its role in solar technology, the use of flat-plate oscillating heat pipes for cooling photovoltaic cells with high concentration ratios, the use of nanoparticles to improve the convective heat transfer at high Reynolds number, the optimization of energy in the end use, and the “field synergy principle” as an effective tool to optimize the energy and mass flow in energy systems.

Predominance of Methanolobus spp. and Methanoculleus spp. in the Archaeal Communities of Saline Gas Field Formation Fluids

The microbial communities in sulfate-rich, saline formation fluids of a natural gas reservoir in Lower Saxony, Germany were investigated to enhance the knowledge about microbial communities in potential carbon dioxide sequestration sites. This investigation of the initial state of the deep subsurface microbiota is necessary to predict their influence on the long-term stability and storage capacity of such sites. While the bacterial 16S rDNA gene library was comprised of sequences affiliating with the Firmicutes, the Alphaproteobacteria, the Gammaproteobacteria and the Thermotogales, the archaeal 16S rDNA libraries were simply dominated by two phylotypes related to the genera Methanolobus and Methanoculleus. The monitoring of the archaeal communities in different formation fluid samples by T-RFLP and Real-Time-PCR indicated that these two methanogenic genera dominated at all, whereas the proportion of the two groups varied. Thus, methylotrophic and autotrophic methanogenesis seems to be of importance in the reservoir fluids, dependent on the provided reduction equivalents and substrates and it also may influence the fate of CO2 in the subsurface.

Numerical simulations on the influence of matrix diffusion to carbon sequestration in double porosity fissured aquifers

The double porosity model for fissured rocks, such as limestones and dolomites, has some features that may be relevant for carbon sequestration. Numerical simulations were conducted to study the influence of matrix diffusion on the trapping mechanisms relevant for the long-term fate of CO 2 injected in fissured rocks. The simulations show that, due to molecular diffusion of CO 2 into the rock matrix, dissolution trapping and hydrodynamic trapping are more effective in double porosity aquifers than in an equivalent porous media. Mineral trapping, although assessed indirectly, is also probably more relevant in double porosity aquifers due to the larger contact surface and longer contact time between dissolved CO 2 and rock minerals. However, stratigraphic/structural trapping is less efficient in double porosity media, because at short times CO 2 is stored only in the fissures, requiring large aquifer volumes and increasing the risk associated to the occurrence of imperfections in the cap-rock through which leakage can occur. This increased risk is also a reality when considering storage in aquifers with a regional flow gradient, since the CO 2 free-phase will move faster due to the higher flow velocities in fissured media and discharge zones may be reached sooner.

The effects of gas-fluid-rock interactions on CO2 injection and storage: Insights from reactive transport modeling

Abstract Possible means of reducing atmospheric CO 2 emissions include injecting CO 2 in petroleum reservoirs for Enhanced Oil Recovery or storing CO 2 in deep saline aquifers. Large-scale injection of CO 2 into subsurface reservoirs would induce a complex interplay of multiphase flow, capillary trapping, dissolution, diffusion, convection, and chemical reactions that may have significant impacts on both short-term injection performance and long-term fate of CO 2 storage. Reactive Transport Modeling is a promising approach that can be used to predict the spatial and temporal evolution of injected CO 2 and associated gas-fluid-rock interactions. This presentation will summarize recent advances in reactive transport modeling of CO 2 storage and review key technical issues on (1) the short- and long-term behavior of injected CO 2 in geological formations; (2) the role of reservoir mineral heterogeneity on injection performance and storage security; (3) the effect of gas mixtures (e.g., H 2 S and SO 2 ) on CO 2 storage; and (4) the physical and chemical processes during potential leakage of CO 2 from the primary storage reservoir. Simulation results suggest that CO 2 trapping capacity, rate, and impact on reservoir rocks depend on primary mineral composition and injecting gas mixtures. For example, models predict that the injection of CO 2 alone or co-injection with H 2 S in both sandstone and carbonate reservoirs lead to acidified zones and mineral dissolution adjacent to the injection well, and carbonate precipitation and mineral trapping away from the well. Co-injection of CO 2 with H 2 S and in particular with SO 2 causes greater formation alteration and complex sulfur mineral (alunite, anhydrite, and pyrite) trapping, sometimes at a much faster rate than previously thought. The results from Reactive Transport Modeling provide valuable insights for analyzing and assessing the dynamic behaviors of injected CO 2 , identifying and characterizing potential storage sites, and managing injection performance and reducing costs.

Post-closure migration for CO2 geological storage and regional pressure inferences

Abstract The geological storage of CO 2 usually considers 4 stages such as exploration, operation, closure and post closure. To ensure safe behavior during the closure and post-closure stages, long term migration scenarios must be considered. In particular, the fate of CO 2 will be controlled by the pressure behavior of the storage reservoir and the regional hydrodynamics. The main migration mechanisms such as buoyancy, dissolution, capillary and mineral trapping will be enhanced depending on the local conditions in the storage reservoir and its geosphere. This paper aims at estimating the long term behavior of CO 2 for a proposed injection in an on shore brine aquifer. This work will consider the whole storage cycle (injection and post closure). To estimate the post-closure migration of CO 2 , the comprehensive geological and dynamical knowledge must be integrated for the reservoir and its geosphere. This 3-D model must also account for regional hydrodynamics of the aquifers and encompass all formations between reservoir and surface along with their petrophysical description to catch the key geological features that might influence the CO 2 migration thus defining the storage complex. This paper will focus on the definition of the storage complex (c.a. 205x205 km 2 and 2–3 km thick depending on the storage depth). The storage is in hydraulic communications with neighboring oil fields through a common aquifer. The flow model should encompass all these oil reservoirs to enable proper modeling of the pressure and CO 2 interference. Such large scale model imply hypothesis on the boundary and initial (at storage closure) conditions within the domain e.g. pressure and fluid description in the different oil fields due to their independent industrial oil operations which influence the CO 2 migration. This paper illustrates the regional interactions that may take place around a CO 2 storage due to competing activities. It reviews the key features and assumption required to establish the reservoir complex model given its scale both in space and time.

The fate of CO2 bubble leaked from seabed

Abstract A numerical model of an individual CO2 bubble dissolution and ascent in shallow seawater was developed to simulate the fate of CO2 leaked from seabed naturally or artificially. The model consists of a solubility sub-model of CO2 gas in seawater, a CO2 bubble mass transfer sub-model, and a CO2 bubble momentum transfer sub-model. The model is applied to predict the dynamics of leaked CO2 in seawater at various depths from 0–150 m (temperature from 10 ∘C to 25 ∘C) and for initial bubble sizes from 3.0 to 40.0 mm in diameter. A diagram of CO2 ascending distance vs dissolution time is obtained from model simulations. It is found that CO2 bubbles ascend at a mean speed of 16 cm/sec and a mean shrinking rate of 30 × 1 0 − 3 mm/s in diameter approximately if leaked from a shallow ocean ( 150 m) seabed. A parameter, named as critical depth, is defined and suggested as a parameter to indicate if the CO2 leaked from seabed can return to atmosphere. This critical depth is approximately linearly related to the initial bobble size with a gradient of −0.68 m/mm under seawater conditions in the simulation ocean.