Movement Of CO2 Research Articles

Three Methods of Estimating Mesophyll Conductance Agree Regarding its CO₂ Sensitivity in the Rubisco-Limited Ci Range.

Whether the mesophyll conductance to CO2 movement (gm) within leaves of C3 plants changes with CO2 concentration remains a matter of debate, particularly at low CO2 concentrations. We tested for changes in gm over the range of sub-stomatal CO2 concentrations (Ci) for which Rubisco activity limited photosynthesis (A) in three plant species grown under the same conditions. Mesophyll conductance was estimated by three independent methods: the oxygen sensitivity of photosynthesis, variable J fluorescence combined with gas exchange, and the curvature of the Rubisco-limited A vs. Ci curve. The latter assay used a new method of rapidly obtaining data points at approximately every 3 μmol mol−1 for Rubisco-limited A vs. Ci curves, allowing separate estimates of curvature over limited Ci ranges. In two species, soybean and sunflower, no change in gm with Ci was detected using any of the three methods of estimating gm. In common bean measured under the same conditions as the other species, all three methods indicated large decreases in gm with increasing Ci. Therefore, change in gm with Ci in the Rubsico-limited region of A vs. Ci curves depended on the species, but not on the method of estimating gm.

Climate Stability and Fossil Carbon-Based Energy Production—Unbreakable Opposites? Theses for an Attempt to Systematically Describe the Science of Overcoming Climate Change

Recognizing climate change as a consequence of rising atmospheric CO2 concentration, due to massive use of fossil carbon for energy production, has resulted in the need to find alternative sources for energy supply independent from carbon. Success has been poor, and consumption of fossil carbon is rising. Hence, CO2 concentration in the atmosphere is increasing, exacerbating climate change. So the question is: what can be done to change this situation so that energy supply remains abundant but climate is not endangered? Biotechnology is appropriate to control atmospheric CO2 concentration, which is the result of natural CO2 movement, technically performed liberation of CO2 from fossil materials, and biologically driven capture of CO2 out of the atmosphere. In this work, basic considerations are made and formulated to elucidate carbon behavior as well as carbon use in relation to its action on climate. Conclusions are drawn considering CO2 in its dual function as waste of energy production and raw material for energy-containing products, suggesting introduction of CO2 waste management, suggesting introduction of global CO2 monitoring, suggesting revision of the connections between industry and agriculture, forestry and aquaculture (AFA), and considering growth of plants on oceanic surface as well as storage of plant residuals on oceanic floor as voluminous reserves for uptake and storage of atmospheric CO2 enabling regulation of climate development.

Long-term viability of carbon sequestration in deep-sea sediments.

Sequestration of carbon dioxide in deep-sea sediments has been proposed for the long-term storage of anthropogenic CO2 that can take advantage of the current offshore infrastructure. It benefits from the negative buoyancy effect and hydrate formation under conditions of high pressure and low temperature. However, the multiphysics process of injection and postinjection fate of CO2 and the feasibility of subseabed disposal of CO2 under different geological and operational conditions have not been well studied. With a detailed study of the coupled processes, we investigate whether storing CO2 into deep-sea sediments is viable, efficient, and secure over the long term. We also study the evolution of multiphase and multicomponent flow and the impact of hydrate formation on storage efficiency. The results show that low buoyancy and high viscosity slow down the ascending plume and the forming of the hydrate cap effectively reduces permeability and finally becomes an impermeable seal, thus limiting the movement of CO2 toward the seafloor. We identify different flow patterns at varied time scales by analyzing the mass distribution of CO2 in different phases over time. We observe the formation of a fluid inclusion, which mainly consists of liquid CO2 and is encapsulated by an impermeable hydrate film in the diffusion-dominated stage. The trapped liquid CO2 and CO2 hydrate finally dissolve into the pore water through diffusion of the CO2 component, resulting in permanent storage. We perform sensitivity analyses on storage efficiency under variable geological and operational conditions. We find that under a deep-sea setting, CO2 sequestration in intact marine sediments is generally safe and permanent.

A Comprehensive Overview of CO2 Flow Behaviour in Deep Coal Seams

Although enhanced coal bed methane recovery (ECBM) and CO2 sequestration are effective approaches for achieving lower and safer CO2 levels in the atmosphere, the effectiveness of CO2 storage is greatly influenced by the flow ability of the injected CO2 through the coal seam. A precious understanding of CO2 flow behaviour is necessary due to various complexities generated in coal seams upon CO2 injection. This paper aims to provide a comprehensive overview on the CO2 flow behaviour in deep coal seams, specifically addressing the permeability alterations associated with different in situ conditions. The low permeability nature of natural coal seams has a significant impact on the CO2 sequestration process. One of the major causative factors for this low permeability nature is the high effective stresses applying on them, which reduces the pore space available for fluid movement with giving negative impact on the flow capability. Further, deep coal seams are often water saturated where, the moisture behave as barriers for fluid movement and thus reduce the seam permeability. Although the high temperatures existing at deep seams cause thermal expansion in the coal matrix, reducing their permeability, extremely high temperatures may create thermal cracks, resulting permeability enhancements. Deep coal seams preferable for CO2 sequestration generally are high-rank coal, as they have been subjected to greater pressure and temperature variations over a long period of time, which confirm the low permeability nature of such seams. The resulting extremely low CO2 permeability nature creates serious issues in large-scale CO2 sequestration/ECBM projects, as critically high injection pressures are required to achieve sufficient CO2 injection into the coal seam. The situation becomes worse when CO2 is injected into such coal seams, because CO2 movement in the coal seam creates a significant influence on the natural permeability of the seams through CO2 adsorption-induced swelling and hydrocarbon mobilisation. With regard to the temperature, the combined effects of the generation of thermal cracks, thermal expansion, adsorption behaviour alterations and the associated phase transition must be considered before coming to a final conclusion. A reduction in coal’s CO2 permeability with increasing CO2 pressure may occur due to swelling and slip-flow effects, both of which are influenced by the phase transition in CO2 from sub- to super-critical in deep seams. To date, many models have been proposed to simulate CO2 movement in coal considering various factors, including porosity, effective stress, and swelling/shrinkage. These models have been extremely useful to predict CO2 injectability into coal seams prior to field projects and have therefore assisted in implementing number of successful CO2 sequestration/ECBM projects.

The Application of Support Vector Machine (SVM) Regression Method in Tunnel Fires

Abstract Due to the relatively closed and narrow space of tunnel, when the fire happens, smoke spreads rapidly and evacuation is difficult. Because the conditions are changing of smoke and temperature distributions after fire burning with different situations, such as ventilation mode and fire source character and so on, it is important to study all the related issues with various fire conditions and find the optimal fire proof design method. This paper takes a fire prevention zone of a real highway tunnel as the reduced scale model (1:9) of tunnel fire test platform. The orthogonal tests of fire in tunnel model under different situations are carried out, with different fire heat release rates and ventilation velocities and fire source locations. The support vector machine (SVM) regression method is used to analyze the CO concentration and temperature in two references firstly, which shows the availability for tunnel fires in steady stage. Then CO2 gas concentration and movement are analyzed during the fire initial burning state based on the SVM regression method for our experiments. It is revealed that CO2 gas concentration in different situations can be predicted during the fire burning initial stage, and the orthogonal tests accompanied with the SVM regression can indicate the influence of various fire conditions for concentration and further guide the experiment scheme.

Mesophyll conductance in Zea mays responds transiently to CO2 availability: implications for transpiration efficiency in C4 crops.

Mesophyll conductance (gm ) describes the movement of CO2 from the intercellular air spaces below the stomata to the site of initial carboxylation in the mesophyll. In contrast with C3 -gm , little is currently known about the intraspecific variation in C4 -gm or its responsiveness to environmental stimuli. To address these questions, gm was measured on five maize (Zea mays) lines in response to CO2 , employing three different estimates of gm . Each of the methods indicated a significant response of gm to CO2 . Estimates of gm were similar between methods at ambient and higher CO2 , but diverged significantly at low partial pressures of CO2 . These differences are probably driven by incomplete chemical and isotopic equilibrium between CO2 and bicarbonate under these conditions. Carbonic anhydrase and phosphoenolpyruvate carboxylase invitro activity varied significantly despite similar values of gm and leaf anatomical traits. These results provide strong support for a CO2 response of gm in Z.mays, and indicate that gm in maize is probably driven by anatomical constraints rather than by biochemical limitations. The CO2 response of gm indicates a potential role for facilitated diffusion in C4 -gm . These results also suggest that water-use efficiency could be enhanced in C4 species by targeting gm .

Assessment of CO2 Geological Storage Potential in a Depleted Oil Field in the North of Thailand

Recently, climate change is the major environmental concern due to the emission of Carbon dioxide (CO2) into atmosphere. The CO2 sources mainly come from power generation. The current technology used to mitigate and store CO2 is carbon capture and storage (CCS) especially geological storage. In Thailand, CCS technology is still infant and less research has been studied. Therefore, this work is focused on the simulation study on the CO2 onshore geological storage in a depleted oilfield in the North of Thailand. The model with local grid refinement demonstrates how CO2 injected into the oilfield can be implemented with the flow rate from 1000-4000 tons/day based on the depth of this area around 2450-2550 meters. The pressure distribution and the movement of CO2 have been studied and predicted within a period of 50 years for CO2 monitoring. The results present that 16 Mt of CO2 storage can be achieved. Furthermore, pressure distribution and CO2 migration are presented without breaking the caprock formation for 50 years. This study can be used as a basic model for CO2 storage in an onshore area in Thailand.

Linking the local vertical variability of permeability and porosity to newly-interpreted lithofacies in the lower Mt. Simon CO2 reservoir

A full understanding of the subsurface processes relevant to CO2 geo-sequestration, including CO2 movement and trapping, requires establishing basic relationships between the sedimentary architecture in CO2 reservoirs and the associated variations in petrophysical attributes that can affect plume dynamics and residual CO2 trapping. In this context, the variance and covariance of petrophysical attributes of the lower Mt. Simon Sandstone reservoir (Illinois, USA) are quantitatively decomposed according to sedimentary textures and structures that vary among sedimentary facies. Building on Ritzi et al. (2016), the sedimentary facies of the lower Mt. Simon are re-classified with new interpretations of sedimentary structures. A newly-revised methodology is used in which factor interactions are formally quantified and the magnitude of their contribution to the variance is compared to the main-factor effects. The decomposition results show the main-factor effects contributing to the variance of permeability and porosity are the differences in grain-size and the presence or absence of bleaching textures. The differences in permeability or porosity among the newly defined sedimentary structures make a relatively small contribution to the sample variance, and the 2-way and 3-way factor interactions are negligible. Permeability and porosity increase with coarser grain size, independent of the presence or absence of bleaching and independent of sedimentary structure. The presence of bleaching textures reduces permeability and porosity independent of the grain size or sedimentary structure. The general approach and these specific results aid in developing parsimonious reservoir simulation models.

Monitoring field scale CO2 injection from time-lapse seismic and well log, integrating with advanced rock physics model at Cranfield EOR site

Causes and effects of global warming have been highly debated in recent years. Nonetheless, injection and storage of CO2 (CO2 sequestration) in the subsurface is becoming increasingly accepted as a viable tool to reduce the amount of CO2 from the atmosphere, which is a primary contributor to global warming. Monitoring of CO2 movement with time is essential to ascertain that sequestration is not hazardous. A method is proposed here to appraise CO2 saturation from seismic attributes using differential effective medium theory modified for pressure (PDEM). The PDEM theory accounts pressure-induced fluid flow between cavities, which is a very important investigation in the CO2-sequestered regime of heterogeneous microstructure. The study area is the lower Tuscaloosa formation at Cranfield in Mississippi, USA, which is one of the active enhanced oil recovery (EOR), and CO2 capture and storage (CCS) fields. Injection well (F1) and two observation wells (F2 and F3) are present close (within 112 m) to the detailed area of study for this region. Since the three wells are closely situated, two wells, namely injection well F1 and the furthest observation well F3, have been focused on to monitor CO2 movement. Time-lapse (pre- and post-injection) log, core and surface seismic data are used in the quantitative assessment of CO2 saturation from the PDEM theory. It has been found that after approximately 9 months of injection, average CO2 saturations in F1 and F3 are estimated as 50% in a zone of thickness ~ 25 m at a depth of ~ 3 km.

Nanoscale Chemical Processes Affecting Storage Capacities and Seals during Geologic CO2 Sequestration.

Geologic CO2 sequestration (GCS) is a promising strategy to mitigate anthropogenic CO2 emission to the atmosphere. Suitable geologic storage sites should have a porous reservoir rock zone where injected CO2 can displace brine and be stored in pores, and an impermeable zone on top of reservoir rocks to hinder upward movement of buoyant CO2. The injection wells (steel casings encased in concrete) pass through these geologic zones and lead CO2 to the desired zones. In subsurface environments, CO2 is reactive as both a supercritical (sc) phase and aqueous (aq) species. Its nanoscale chemical reactions with geomedia and wellbores are closely related to the safety and efficiency of CO2 storage. For example, the injection pressure is determined by the wettability and permeability of geomedia, which can be sensitive to nanoscale mineral-fluid interactions; the sealing safety of the injection sites is affected by the opening and closing of fractures in caprocks and the alteration of wellbore integrity caused by nanoscale chemical reactions; and the time scale for CO2 mineralization is also largely dependent on the chemical reactivities of the reservoir rocks. Therefore, nanoscale chemical processes can influence the hydrogeological and mechanical properties of geomedia, such as their wettability, permeability, mechanical strength, and fracturing. This Account reviews our group's work on nanoscale chemical reactions and their qualitative impacts on seal integrity and storage capacity at GCS sites from four points of view. First, studies on dissolution of feldspar, an important reservoir rock constituent, and subsequent secondary mineral precipitation are discussed, focusing on the effects of feldspar crystallography, cations, and sulfate anions. Second, interfacial reactions between caprock and brine are introduced using model clay minerals, with focuses on the effects of water chemistries (salinity and organic ligands) and water content on mineral dissolution and surface morphology changes. Third, the hydrogeological responses (using wettability alteration as an example) of clay minerals to chemical reactions are discussed, which connects the nanoscale findings to the transport and capillary trapping of CO2 in the reservoirs. Fourth, the interplay between chemical and mechanical alterations of geomedia, using wellbore cement as a model geomedium, is examined, which provides helpful insights into wellbore and caprock integrities and CO2 mineralization. Combining these four aspects, our group has answered questions related to nanoscale chemical reactions in subsurface GCS sites regarding the types of reactions and the property alterations of reservoirs and caprocks. Ultimately, the findings can shed light on the influences of nanoscale chemical reactions on storage capacities and seals during geologic CO2 sequestration.

Understanding the Effects Small Scale Heterogeneity on Buoyancy Driven CO2 Migration for Capillary Trapped Storage Capacity Estimation

During geologic carbon sequestration, the long term movement and migration of CO2 occurring far from the wells, is majorly controlled by the interplay between buoyancy and capillary forces. Geological heterogeneity, which is well known to affect the fluid flow in the subsurface, becomes an even more pronounced influence in capillary dominated flows. In such cases, core-flooding and numerical experiments have shown that capillary pressure contrasts due to small scale heterogeneities can affect the flow path of the invading CO2 resulting in back filling and accumulation beneath capillary barriers. In this work, we investigate the impact of small-scale heterogeneity on CO2 trapping capacity by simulating the migration of CO2 through nature mimicking high resolution geological domains. Realistic sedimentary 3D models to be used as flow domains are generated for 4 common fluvial clastic facies with accurately represented bedform morphology. The models are populated with petrophysical parameters representative of sandstone lithologies with different grain sizes and sorting. A modified invasion percolation simulator is employed to enable the use of high resolution models and capture the relevant flow physics. Results from these simulations provide insight into how the saturation aka the storage capacity is a non-linear function of the capillary contrast, which suggests some predictive ability is achievable from common sedimentological descriptors.

Rock Mechanical Approaches for Predicting Fault Behaviour During CO2 Injection

This paper presents the pre-injection fault characterisation that has been conducted at the CO2CRC Otway Project in Victoria, Australia, aimed at understanding the response of faults to pressure increases in the formation, fault transmissibility horizontally and vertically, and also presents a methodology to extract key rheological fault properties using novel rock mechanical techniques. The initial modelling results show that the likelihood of injection induced fault reactivation is exceedingly small, due to the very small pressure increases associated with injection (∼ 0.05 MPa after about 100 days of injection during the Stage 2C experiment). The potential for CO2 flow across the main reservoir-cutting faults was quantified using the shale gouge ratio algorithm. Results indicate that the faults should be sealing to some degree and should therefore restrict the lateral movement of CO2. Despite these positive results with regard to fault behaviour during current operations, there remains significant uncertainty with regard to certain fault properties such as friction and cohesion that have a large effect on fault stability. Here we develop a workflow which involves several rock mechanical testing techniques to gain information regarding a key fault at the Otway site. One relatively novel technique that is used is the scratch test, which measures strength heterogeneity of the host rock at the centimetre scale. The scratch data can be correlated to certain well logs via a multivariate analysis in order to develop proxies for rock strength that can be applied to other wells and also to wells that traverse fault zones, thereby providing some estimate of fault strength. This scratch analysis is complemented by a series of triaxial experiments designed to measure poroelastic properties and also assess the rate and state frictional parameters of potential fault gouge materials. While the work presented here is aimed specifically at understanding the properties of key faults at the Otway Project, it is hoped that the knowledge gained and the transforms developed here can be used as a guide to constrain fault properties at other CCS sites.

Investigating the Influence of Geological Heterogeneity on Capillary Trapping of Buoyant CO2 Using Transmitted-light Flow Visualization Experiments

Small scale heterogeneity characteristic of clastic formations has been well known to affect CO2 migration pathways during geologic carbon sequestration. Especially far field from the injection sites, when buoyancy and capillary forces take over from the injection pressure gradients, the effects of such geological features on the CO2 plume movement become compounded. Numerical simulations have established that accumulation and trapping of the buoyant plume is primarily due to the contrast in capillary entry pressures of different rock layers. Capillary trapping can help maximize the storage capacity of reservoirs and hence it is essential to understand the dynamics of CO2 movement and trapping under the influence of small scale heterogeneity and quantify its effects. In this work we propose buoyancy driven migration experiments and simulations conducted at the meter scale using glass beads packed in a quasi 2D glass cell. Using a combination of two linear axis actuators, we demonstrate an automated glass bead filler system that can generate 2D heterogeneous structures in a reproducible manner. A fluid pair that mimics the phase densities and viscosities of CO2-Brine at reservoir pressures and temperatures is employed. Light transmission technique is used for visualization, and to calibrate and quantify saturation of the trapped non-wetting fluid during the experiments. Invasion Percolation is used to simulate the buoyancy driven flow. With the ability to generate different types of heterogeneous structures in a reproducible manner, and by comparing experiments and simulations, a systematic investigation of the effect of heterogeneity on capillary trapping becomes possible.

Investigation of relative flow characteristics of brine-saturated reservoir formation: A numerical study of the Hawkesbury formation

Precise knowledge of the relative flow behaviour of CO2 and brine during CO2 sequestration in deep saline aquifers and its impact on the sequestration process is required to ensure the safety and efficiency of sequestration projects. This numerical study therefore aims to identify the interaction-induced relative flow behaviour of reservoir rock and its influence on the hydro-mechanical and geochemical phenomena in deep saline aquifers. COMSOL Multiphysics numerical simulator was used to develop a laboratory-scale relative flow model to simulate the CO2 movement and brine drainage processes in brine-saturated Hawkesbury sandstone samples and finally, was extended it into a field-scale numerical model which can simulate the hydro-mechanical, mineralogical and geochemical behaviours of deep saline aquifers under CO2 sequestration conditions. A 2-D axisymmetric pore-elastic model was developed using the pore-elastic module available in COMSOL and Buckely-Leverett flow theory was applied to the model using pre-defined partial differential equations. The proposed laboratory-scale model was first validated using experimental permeability data conducted under triaxial drained conditions and the model was then extended to predict relative flow characteristics, such as brine and CO2 saturation and CO2 pressure distribution along the sample length under different injection pressures, including both sub- and super-critical conditions and finally, real CO2 sequestration processes.According to the results, the developed laboratory-scale model simulates the experimental results reasonably well with less than 10% relative error. The numerical results also reveal that there is a considerable effect of CO2 phase change on the final distribution of the CO2 and brine saturation profiles. In addition, the CO2 pressure distribution along the sample length shows a non-linear relationship between the CO2 pressure and sample length. According to the results of the field-scale model, the long-term interaction of CO2 causes Hawkesbury formation's pore structure to significantly change.

Simulating microbial denitrification with EPIC: Model description and evaluation

Microbial denitrification occurs in anaerobic soil microsites and aquatic environments leading to production of N2O and N2 gases, which eventually escape to the atmosphere. Atmospheric concentrations of N2O have been on the rise since the beginning of the industrial revolution due to large-scale manipulations of the N cycle in managed ecosystems, especially the use of synthetic nitrogenous fertilizer. Here we document and test a microbial denitrification model identified as IMWJ and implemented as a submodel in the EPIC terrestrial ecosystem model. The IMWJ model is resolved on an hourly time step using the concept that C oxidation releases electrons that drive a demand for electron acceptors such as O2 and oxides of N (NO3−, NO2−, and N2O). A spherical diffusion approach is used to describe O2 transport to microbial surfaces while a cylindrical diffusion method is employed to depict O2 transport to root surfaces. Oxygen uptake by microbes and roots is described with Michaelis-Menten kinetic equations. If insufficient O2 is present to accept all electrons generated, the deficit for electron acceptors may be met by oxides of nitrogen, if available. The movement of O2, CO2 and N2O through the soil profile is modeled using the gas transport equation solved on hourly or sub-hourly time steps. Bubbling equations also move N2O and N2 through the liquid phase to the soil surface under highly anaerobic conditions. We used results from a 2-yr field experiment conducted in 2007 and 2008 at a field site in southwest Michigan to test the ability of EPIC, with the IMWJ option, to capture the non-linear response of N2O fluxes as a function of increasing rates of N application to maize [Zea mays L.]. Nitrous oxide flux, soil inorganic N, and ancillary data from 2007 were used for EPIC calibration while 2008 data were used for independent model validation. Overall, EPIC reproduced well the timing and magnitude of N2O fluxes and NO3− mass in surficial soil layers after N fertilization. Although similar in magnitude, daily and cumulative simulated N2O fluxes followed a linear trend instead of the observed exponential trend. Further model testing of EPIC+IMWJ, alone or in ensembles with other models, using data from comprehensive experiments will be essential to discover areas of model improvement and increase the accuracy of N2O predictions under a wide range of environmental conditions.

CO2–Water–Rock Wettability: Variability, Influencing Factors, and Implications for CO2 Geostorage

Carbon geosequestration (CGS) has been identified as a key technology to reduce anthropogenic greenhouse gas emissions and thus significantly mitigate climate change. In CGS, CO2 is captured from large point-source emitters (e.g., coal fired power stations), purified, and injected deep underground into geological formations for disposal. However, the CO2 has a lower density than the resident formation brine and thus migrates upward due to buoyancy forces. To prevent the CO2 from leaking back to the surface, four trapping mechanisms are used: (1) structural trapping (where a tight caprock acts as a seal barrier through which the CO2 cannot percolate), (2) residual trapping (where the CO2 plume is split into many micrometer-sized bubbles, which are immobilized by capillary forces in the pore network of the rock), (3) dissolution trapping (where CO2 dissolves in the formation brine and sinks deep into the reservoir due to a slight increase in brine density), and (4) mineral trapping (where the CO2 introduced into the subsurface chemically reacts with the formation brine or reservoir rock or both to form solid precipitates). The efficiency of these trapping mechanisms and the movement of CO2 through the rock are strongly influenced by the CO2-brine-rock wettability (mainly due to the small capillary-like pores in the rock which form a complex network), and it is thus of key importance to rigorously understand CO2-wettability. In this context, a substantial number of experiments have been conducted from which several conclusions can be drawn: of prime importance is the rock surface chemistry, and hydrophilic surfaces are water-wet while hydrophobic surfaces are CO2-wet. Note that CO2-wet surfaces dramatically reduce CO2 storage capacities. Furthermore, increasing pressure, salinity, or dissolved ion valency increases CO2-wettability, while the effect of temperature is not well understood. Indeed theoretical understanding of CO2-wettability and the ability to quantitatively predict it are currently limited although recent advances have been made. Moreover, data for real storage rock and real injection gas (which contains impurities) is scarce and it is an open question how realistic subsurface conditions can be reproduced in laboratory experiments. In conclusion, however, it is clear that in principal CO2-wettability can vary drastically from completely water-wet to almost completely CO2-wet, and this possible variation introduces a large uncertainty into trapping capacity and containment security predictions.

The latest monitoring progress for Shenhua CO2 storage project in China

Shenhua Ordos CCS project is the first full-ranged demonstration project including CO2 capture, transportation and storage in China. In order to ensure the safety of CO2 storage in the saline aquifers, the monitoring scheme was designed and detailed monitoring data was obtained. The whole monitoring schemes include under-ground, ground and above-ground monitoring at the pre-determined monitoring heights. Vertical Seismic Profile (VSP) monitoring results of three times indicate that the migration of the injected CO2 stays within 450m around the injection well. No CO2 vertically leaked to the surface. Other monitoring results did not show any leakage from the saline aquifer, which further proves the safety of CO2 storage in the saline aquifers. Continuous monitoring is required to further track the CO2 movement and to ensure the safety of CO2 saline storage over time.

Representative Elementary Volume (REV) in spatio-temporal domain: A method to find REV for dynamic pores

One of the potential risks associated with subsurface storage of CO2 is the seepage of CO2 through existing faults and fractures. There have been a number of studies devoted to this topic. Some of these studies show that geochemistry, especially mineralization, plays an important role in rendering the faults as conduits for CO2 movement while others show that mineralization due to CO2 injection can result in seep migration and flow diversion. Therefore, understanding the changes in reservoir properties due to pore alterations is important to ensure safe long term CO2 storage in the subsurface. We study the changes in the Representative Elementary Volume (REV) of a rock due to reactive kinetics over a time, using a statistical approach and pore-scale CO2-rock interactiondata. The goal of this study is to obtain the REV of a rock property that accounts for pore-scale changes over time due to reactive kinetics, and we call this as spatiotemporal REV. Scale-up results suggest that the REV changes with time when CO2-rock interaction is considered. It is hypothesized that the alteration in pore structure introduces more heterogeneity in the rock, and because of this the magnitude of REV increases. It is possible that these noticeable changes in REV at pore-scale may have an impact when analyzed at the reservoir scale.

Numerical study of the interplay between thermo-topographic slope flow and synoptic flow on canopy transport processes

Canopy flow resulting from interaction between thermo-topographic slope flow and large-scale synoptic flow is very complicated and has been poorly understood. We apply a Reynolds-averaged Navier-Stokes (RANS) turbulence model to investigate how the interactions between local flow and synoptic winds affect CO2 movement in the canopy layer at the Renon site in the Italian Alps. Since the RANS simulations are compared to the data measured by multiple-tower experiments conducted during CarboEurope-IP advection campaigns (ADVEX) at Renon, our study can be viewed as a case study of a relatively common wooded slope. The thermal condition in the canopy is directly related to the canopy morphology: the dense canopy at our site causes stronger cooling but limits vertical exchange of heat flux, resulting in weak temperature inversion in the deep canopy. Under conditions with no synoptic wind, local flow leads to CO2 build-up mainly at downslope locations and no recirculation is formed. Recirculation that holds high CO2 mole fraction in the canopy is developed only under the condition that local slope wind is enhanced by northerly synoptic winds. No recirculation forms when southerly synoptic wind direction is opposite to the local wind direction, in which case CO2 is quite well mixed. This numerical study approach brings to light a better understanding of the CO2 closure problem: the measured net ecosystem exchange of CO2 is more likely to be underestimated in local non-synoptic slope flow and local synoptic-enhanced slope flow regimes at Renon. However, small-scale heterogeneity in canopy structure, variability in the CO2 source from soil and higher-resolution and larger-scale topography still challenge the application of this numerical approach in the FLUXNET community.

Simple dielectric mixing model in the monitoring of CO 2 leakage from geological storage aquifer

The principle of the dielectric mixing for multiphase systems in porous media has been employed to investigate CO2–water-porous media system and monitor the leakage of CO2, in analogy to scenarios that can be encountered in geological carbon sequestration. A dielectric mixing model was used to relate the relative permittivity for different subsurface materials connected with the geological carbon sequestration. The model was used to assess CO2 leakage and its upward migration, under the influences of the depth-dependent characteristics of the subsurface media as well as the fault-connected aquifers. The results showed that for the upward migration of CO2 in the subsurface, the change in the bulk relative permittivity (εb) of the CO2–water-porous media system clearly depicts the leakage and movement of CO2, especially at depth shallower than 800 m. At higher depth, with higher pressure and temperature, the relative permittivity of CO2 increases with pressure, while that of water decreases with temperature. These characteristics of water and supercritical CO2, combine to limit the change in the εb, at higher depth. Furthermore, it was noted that if the pore water was not displaced by the migrating CO2, the presence of CO2 in the system increases the εb. But, with the displacement of pore water by the migrating CO2, it was shown how the εb profile decreases with time. Owing to its relative simplicity, composite dielectric behaviour of multiphase materials can be effectively deployed for monitoring and enhancement of control of CO2 movement in the geological carbon sequestration.