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In recent years, the new coronavirus COVID-19 has brought great disaster and loss to the world and is still spreading around the world. The situation in China is generally well controlled, and the lockdown has been removed, but the comments and messages about the epidemic persist online. For people working and living normally in China, their attitudes and views toward COVID-19 directly reflect the current situation of the pandemic. This paper collected Chinese microblogs, forums, and online comments, identified the latest comments about COVID-19, and conducted a sentiment analysis of them. Specifically, we proposed a new sentiment analysis method that integrated the semantics of words with the text analyzed. Different from the traditional sentiment analysis method which only relied on sentiment words, the proposed method extended the semantic concepts of affective words by integrating the semantic conceptual information about the affective words from the context of the comments and thus, provided information to support the final judgment of the affective opinions. The proposed approach incorporated the part-of-speech embedding information along with word embedding and relies on semantic concepts to enhance the emotional expression of words in context. The experimental results showed that by integrating the semantics of words, the accuracy of sentiment analysis is substantially improved, and it also reflected that different semantics of the same word have different influences on sentiment analysis. On several benchmark datasets, there was a 3–6% improvement in accuracy. [ABSTRACT FROM AUTHOR]

• The first observation of water drawing and migration induced by CO 2 -C 3 H 8 hydrate formation in glass sand by MRI. • The location of CO 2 -C 3 H 8 hydrate-induced water migration are uncertain, but growth features are similar. • Water can be drawn from the surrounding sands by the local formation of CO 2 -C 3 H 8 hydrates. • Continuous hydrate growth towards the gas phase induces further upward-climbing of water. Hydrate-induced water migration is an unusual behaviour that occurs in certain hydrate formation processes, such as in the formation of propane-containing hydrate. This study is the first to investigate the continuous, staged processes of constant-volume formation, constant-pressure reformation and exhaust dissociation of CO 2 -C 3 H 8 hydrates using the magnetic resonance imaging (MRI) technique. Real-time MRI images indicate that the formation of CO 2 -C 3 H 8 hydrates draw water from its surroundings, causing the local water saturation to increase. As the concentrated water can further form hydrates and extend to the gas phase, the water appears as though it climbs upward through the glass sand and hydrate zone towards the gas phase. Experiments under different formation pressures indicate that the locations of hydrate-induced water migration are uncertain and depend on hydrate nucleation. The evolution processes of hydrate-induced water migration under different initial pressures have good similarity. In addition, water migration will still occur during the reformation stage. The initial pressure has great effects on both the formation and dissociation of hydrate. In addition, faster dissociation may make the water move upward due to strong gas release. The findings in this study are significant to future research on propane-containing hydrate, especially for hydrate-based seawater desalination applications. [ABSTRACT FROM AUTHOR]

• The convection is visualized in an improved Hele-Shaw cell with high Ra region. • Three stages of diffusion, convection mixing and full development can be found in the convection. • Density difference influences initial time, mixing time and finger development. • Dissolution rate shows a power law relationship with Ra. In this study, we visualized density-driven convection in an improved Hele-Shaw cell at 25 °C and 0.1 MPa by examining the convection mixing process of analogous fluids and total dissolution rates in the high Rayleigh number (Ra) region. The high Ra number was inspired by data referring to the geological reservoir at the Sleipner site. We investigated the effect of the density difference between different fluid pairs on the initial moment and development of convective mixing. Though direct imaging and processing, we examined the convective mixing development regime, finger number density, onset time and movement speed of fingers. The fingering instability and mixing time of miscible fluids were also analysed and show that as the density difference increases, the density of the finger number increases and the fingers quickly merge. The onset time decreases sharply and then becomes stable and is inversely proportional to Ra 2. The convection mixing time has the same tendency but is inversely proportional to Ra. Moreover, the finger speed linearly increases and is directly proportional to the characteristic velocity. The dissolution rate was investigated with the dimensionless convection flux Sherwood number (Sh) and shows a power law relationship with Ra. The density difference accelerates the dissolution rate. The experimental conditions were different from those of real CO 2 geological storage, but this study has implications for predicting the CO 2 dissolution trapping time and accumulation for geological storage of carbon dioxide. [ABSTRACT FROM AUTHOR]

• ScCO 2 injection into Berea sandstone was investigated by using X-ray CT technology. • MB CO 2 injection can be applied in sequestration with high efficiency. • MB CO 2 enhanced dissolution in the early stage of injection and inlet zone. • MB CO 2 permeated into low porosity regions to improve the sweep efficiency. Due to the favorable physical properties of micro bubbles (MBs), MB CO 2 injection into saline aquifers was proposed as a novel, economic, and leak-free underground injection method in the purpose of sequestration. In this study, supercritical CO 2 injection into a Berea sandstone sample at 0.05 mL/min under reservoir conditions was investigated using X-ray CT. Experiments with micro bubble (MB) and normal bubble (NB) CO 2 injection were conducted. The dependence of CO 2 migration on pore space shows macroscopic bypassing via preferential flow paths, as the distribution and saturation of CO 2 were largely influenced by the heterogeneous pore structure. Most CO 2 migrated forwards via three flow paths that formed along the bedding layers with high porosity. The CO 2 distribution was discontinuous, and isolated CO 2 clusters appeared due to the heterogeneity of the pore structure and tortuosity of the flow paths. MB CO 2 migrated into the areas adjacent to major flow paths, forming irregular channels, while NB CO 2 migrated through smooth channels. MB CO 2 breakthrough occurred at 0.18 pore volume (PV), which was larger than NB CO 2. A long breakthrough time reflects high pore space utilization. A significant differences of MB and NB CO 2 in the existing duration of flow paths in the whole displacement period was observed, which reflected higher stability of MB CO 2 in the sample. Additionally, little MB CO 2 was observed near the inlet, suggesting that MBs accelerated dissolution in the early stage of injection (0.02 PV). Smaller saturation and larger volume differences were observed for MB CO 2 compared to NB CO 2 in the early stage because of dissolution. The enhanced dissolution efficiency of MB CO 2 reached 18.7% at 0.02 PV. Moreover, pore space utilization improved because MB CO 2 permeated into regions of low porosity and low flow ability. The improvement in the utilization efficiency reached 4.9% in low-porosity regions. And the storage efficiency was increased up to 23.6%.The results of this study suggest that MB CO 2 injection has higher dissolution and improved pore space utilization, making it an efficient method of CO 2 sequestration in low-porosity regions. [ABSTRACT FROM AUTHOR]

Abstract Natural gas hydrates (NGHs) are a potential energy source for the future. The efficient exploitation of NGHs has been a hot topic of worldwide research. At present, the depressurization is considered as the most effective method for NGHs exploitation. However, the lacking of hydrate decomposition driving force in depressurization anaphase and the ice generation phenomenon haven't been solved effectively. The combination method of depressurization with water flow erosion was carried out in this study. The experimental results indicated that driving force for MH decomposition will be not enough when the exploitation backpressure was higher than 2.4 MPa. The combination of depressurization with water flow erosion will efficiently solve the lacking of drive force for depressurization in anaphase and shorten the time of hydrate exploitation. The existence of chemical potential difference accelerated the hydrate decomposition. [ABSTRACT FROM AUTHOR]

Highlights • The dissolution of brine injection into a CO 2 -filled packed bed was investigated. • An image analysis technique was developed to determine the interfacial area. • The effects of Re, gravity and heterogeneity on the interface were analysis. Abstract Explicit knowledge on the two-phase interface evolution during CO 2 dissolving in brine provides accurate predictions on the subsurface behavior of long-term CO 2 storage. In this research, the interfacial areas of CO 2 -unsaturated brine were dynamically measured during multiphase flow using 3D quantitative analyses. The two-phase interfaces during brine imbibition were divided into three terms based on their attributes, i.e., ganglia, cluster and singlet. The evolution terms of the interfaces were interesting, as their fates showed wide evolution patterns due to the diverging effects of the Reynolds number (fluid velocity × length scale/fluid viscosity) and gravity. The brine bypassed the CO 2 , and the interface evolved with the development of a priority path under a heterogeneity impact. Relying on the approach of the slice-averaged and volumetric measurement, the effects of forces and heterogeneity on the CO 2 -unsaturated brine interface were evaluated on different directions. Linear regression of the clouded data points exploited the validity of the power-law distribution from number of trapped cluster to frequency of interfacial area, and the max interfacial areas and variance decreased, while the mean interfacial area increased with brine saturation. Slice-averaged CO 2 -brine interfacial areas normalized by volume or geometric surface area decreased linearly with the brine saturation at different Reynolds numbers. [ABSTRACT FROM AUTHOR]

Highlights • Dynamic CO 2 injection with different flow rates was visually investigated into three stages. • The saturation gradient existed along the porous media and gradually vanished for low flow rates. • The apparent saturation at breakthrough and steady state were linearly related to the maximum saturation change rate. • Too low or high flow rate resulted in unstable front, relatively low saturation, against the utilization of pore space. • The effect of flow rate on storage and utilization of pore space can be applied to Sleipner CO 2 Storage Project. Abstract This study aimed to investigate dynamic CO 2 drainage using high-resolution magnetic resonance imaging (MRI) technology. Gaseous and supercritical CO 2 were injected downward in brine-saturated porous media at different flow rates at 40 °C/6 MPa and 40 °C/8 MPa. These flow rates (0.015, 0.03 and 0.1 mL/min, under 10 Mt/year), as reflected in, were chosen according to the distance (1 km–100 m) from the injection well. Three stages were found from the change of signal intensity during CO 2 drainage: before the CO 2 front reached the field of view (FOV), breakthrough, and steady state. Channelling or drainage fronts immediately established through the large pores, and CO 2 travelled vertically through these channels until breakthrough. The breakthrough time decreased with increasing flow rates and was longer for ScCO 2 than gCO 2 at the same flow rate, resulting in a longer residence time for ScCO 2 in the sample. At low flow rates, the fingers first established along the larger pore spaces (especially at 0.015 mL/min) and then gradually extended into adjacent regions, resulting in a relatively flat interface. However, at high flow rates, the front moved along the larger pore spaces until breakthrough. The flow patterns for ScCO 2 drainage were more uniform than those for gCO 2 drainage. The pore volume fraction occupied by CO 2 , as a quantitative parameter of the flow pattern, reflected that the sweep efficiency and pore space utilization were optimized at 0.03 mL/min (Ca = 4.35 × 10−9 for gCO 2 and Ca = 1.06 × 10-8 for ScCO 2). The effect of the flow rate on the CO 2 saturation and distribution was analysed. At low flow rates, the saturation gradient along the porous media gradually reduced, but trend to be stable at high flow rates. Additionally, the saturation at breakthrough and steady state were observed to be linearly related to the maximum rate of change in saturation during CO 2 injection. Overly fast drainage results in relatively low saturation and an inhomogeneous distribution. The results can be applied to provide information for enhancing pore space utilization and improving sweep efficiencies during field storage. [ABSTRACT FROM AUTHOR]

A clear understanding of mass transfer properties during fluid injection in porous media is important for safe CO 2 storage. In this study, dynamic experiments were conducted to elucidate transport during brine injection into a gaseous CO 2 -filled packed bed using X-ray CT technology. Homogenous glass beads were packed into the bed. Brine was injected downward at 0.005 and 0.03 mL/min. The CO 2 distribution during brine injection was visualized along the flow direction, which reflected the mechanism transform between displacement and dissolution. The results showed that the distribution was related to the pore structure of the packed bed and flow rates. In addition, CO 2 saturation and concentration profiles were obtained at various time points. CO 2 concentrations predicted from saturation were orders of magnitude lower than equilibrium solubility. An image analysis technique was employed to determine the interfacial area, which was a function of saturation. Local and overall mass transfer coefficients which were correlated with local concentration and specific interfacial areas were calculated. This study provided a quantitative investigation of gas–liquid mass transfer in a packed bed, which contributed a calculated mass transfer rate during CO 2 storage. [ABSTRACT FROM AUTHOR]

As one of the most viable technique, geological sequestration of CO 2 has great potential for storing large amount of the injected CO 2 into brine by dissolution. Understanding the mass transfer of CO 2 into a brine sample is of great importance of CO 2 sequestration. Swelling effect revealing the properties of dissolution play an important role. Other than oil swelling, it is difficult to observe directly using traditional methods due to the imperceptible extent of phase expansion in CO 2 -brine mixture. The combination of X-ray computed tomography and image processing techniques has made it possible to measure multiphase boundaries as well as swelling factors of CO 2 -brine systems at high pressures and elevated temperatures. In this work, a generalized methodology has been proposed and successfully applied. The experimental results show that both the mass transfer and the swelling factor increase with pressure. It is also found that the local contact angel significantly increases when gaseous CO 2 turns into supercritical CO 2 . [ABSTRACT FROM AUTHOR]

The convective mixing process is important for the long-term storage of CO 2 because the chemical mineralization of porous rocks due to CO 2 dissolution will eventually take place. In this paper, density-driven-convection mechanism is investigated in an updated Hele-Shaw cell which adds a sealing device in the middle of the cell with dyed sodium chloride solution and pure water instead of CO 2 -diffusive layer and brine. In the early stages, a crinkling pattern gradually appears on the interface. As time goes on, descending fingers form at the interface and extend straight downward. During the process of convection mixing, the fingers extend downward and coalesce with adjacent fingers before arriving at the bottom of the Hele-Shaw cell. The coalescence of finger leads to a decrease in finger number and an increase in finger diameter, but the shape of the finger remain the same. At the position 4mm below the initial interface, the finger number density increases firstly and then decreases with the time. With the increase of Rayleigh number, the onset time decreases and the finger extends more quickly. The finger extension velocity is proportional to the Ra, t ^(-1/2) and Ra is a linear relationship. [ABSTRACT FROM AUTHOR]

Understanding the residual trapping mechanisms is important to design successful CO 2 storage projects. CO 2 injected in field sequestration site are usually combined with various kinds of impurities. N 2 is the most common component, occupying the highest proportion and relatively large cost for gas separating and purification system. The objective of this study was to concentrate the impact of N 2 content ratio and flow rate on the saturation of CO 2 &N 2 gas mixture for a further economical CO 2 separation and sequestration. The gas mixture is almost homogeneous while the total saturations are higher at two conditions: higher CO 2 proportion with lower flow rate, and lower CO 2 proportion with higher flow rate. Meanwhile, saturation maps at different temperature and pressure have certain differences though some of the fluid properties are almost same. Thus experiments between such conditions are not replaceable as the properties of gases will induce the hydrological and hydraulic variation of flow path. [ABSTRACT FROM AUTHOR]

The density driven convection phenomenon is expected to have a significant and positive role in CO 2 geological storage capacity and safety. The onset and development of density-driven convective on the core scale is critical to understand the mass transfer mechanism. In this paper, laboratory experiments were conducted to investigate the density-driven convective in a vertical tube. The deuterium oxide (D 2 O)/manganese chloride (MnCl 2 ) water solution in water or brine were as an analog for CO 2 -rich brine in original brine. Experiments are repeated with variations in permeability to vary the characteristic Rayleigh number. Based on the MRI technology, the intensity images showed the interface clearly, reflecting the transition from diffusion to convective. With the echo-multi-slice pulse sequence method, the intensity images can be obtained as 2 min 8 s. For the denser fluid pairs, fingers appeared, propagated, coalesced and multi-fingers formed. The finger growth rate of the convective was visualized as three distinct periods: rising, stable and declining. Detailed information regarding the wave number, wave length, onset time and mixing time as functions of Rayleigh number are developed. [ABSTRACT FROM AUTHOR]

The CO 2 stream to be transported and sealed in CCS project usually contains various impurities, and purifying the CO 2 stream costs utmost in the CO 2 capture and storage process. Co-sequestration of impurities with supercritical CO 2 will decline the capture requirement. Few studies have discovered the impact on CO 2 storage capacity at porous scale when remaining non-condensable gas in the CO 2 stream such as N 2 which occupied a large proportion in flue gas stream. We performed comparison experiments between different N 2 proportion, capillary number, temperatures and pressures to discover preliminary research on the performance of CO 2 containing N 2 by X-ray CT scanning. The 3-D saturation distributions implies the higher temperatures and pressures slightly increase the saturation and such gas flow will show priority at small scale heterogeneity for the same capillary number. Meanwhile when the N 2 proportion increase, the saturation will slightly promoted at high porosity region, and vice versa. However at the logCa=-7.5, the high N 2 percentage in CO 2 stream at high temperature and pressure reveal strong assets among the whole porosity region. Under such conditions the saturation of gas mixture achieves relative high values and enhances the CO 2 storage capacity. [ABSTRACT FROM AUTHOR]

Faster dissolution of CO 2 within aquifers plays a crucial role in the optimal storage of carbon dioxide injected into reservoirs. The mixture of CO 2 and brine triggers convection currents in the aquifer and creates a remarkable increase of the dissolution rate of carbon dioxide. It is very vital for the risk assessment of leakage to obtain accurate description of the CO 2 dissolution rate in the aquifers. In our experiments a series of CO 2 solute-driven convection laboratory tests were performed in transparent vertical Hele-Shaw cells with a 1.2 mm gap that contained brine water overlain by gas phase and visualization of convective phenomena was achieved with the help of bromocresol purple completely solved into the brine at first. After CO 2 -brine film come to existence, small phase fingers caused by density contrast would form and they merge, widen, and penetrate deep into the cell. Much series of images recording the dynamic convection were analyzed. Binarization process can help calculate timescale changes of average/all rich- CO 2 -area which present mass transfer rate of CO 2 into the brine. Effects of such different formation parameters as brine concentration, temperature, high pressure and heterogeneity on the onset and development of convection are investigated in our study. Two time intervals, including onset time and developing time took our most attention. Increasing system Rayleigh number, the formation parameters can greatly strengthen the convective mixing and accelerate the growth of CO 2 solution into the test cell. The sodium chloride solution concentration gradient has an obvious influence on the form and development of convection phenomenon in our experiments. Here, only part results are exhibited in this paper and much further work are under way. [ABSTRACT FROM AUTHOR]

To study CO 2 flow characteristics in heterogeneous rock, we designed a laboratory experimental system that visualizes the CO 2 movements in rock specimens by using X-ray computed tomography (CT). We carried out laboratory experiments of CO 2 flooding in porous sandstones, together with porosity calculation, fluid saturation monitoring based on the CT images and mass flow measurements for ejected fluids. We used Berea sandstone and Sarukawa sandstone as homogeneous and heterogeneous rock in this study. The CO 2 flooding tests were carried out until the CO 2 injection reaches about 2 PV (pore volume) for the Berea sandstone and about 3 PV for the Sarukawa sandstone. When injected CO 2 reached 1.0 PV in both specimens, The CO 2 saturations were 34.15% and 15.21% in Berea sandstone and Sarukawa sandstone, respectively. We increased the differential pressure only for the Sarukawa sandstone to confirm the influence of differential pressure on CO 2 saturation and oil recovery in heterogeneous media. The oil recoveries were 74.80% and 71.93% for Berea sandstone and Sarukawa sandstone, respectively when injected CO 2 reached about 2.0 PV. CO 2 was spreading evenly from the injection part through the Berea sandstone. In the case of Sarukawa sandstone, almost all of the CO 2 preferentially moved through the upper part of specimen. This represents that the sedimentation heterogeneity is one of the main factors that affects the CO 2 flooding pattern. [ABSTRACT FROM AUTHOR]

Deep Saline aquifers are promising long-term storage sites for CO 2 emissions. The injection pressure is one of major factor that determines CO 2 migration phase equilibrium, and the flow rate influences the injectivity behavior and plume migration. However, data and knowledge of the injection pressure and the variation of velocity in displacement process are scarce. In this paper, we describe a set of laboratory tests on two–phase flow drainage of CO 2 and brine. Fundamental characteristics such as the CO 2 front, the breakthrough time and sweep efficiency, residual water saturation, due to the injection pressure and rate of displacement fluid was explored. The measurement is conducted at 40 °C under two different pressure conditions and four CO 2 injection rate, representative of a CO 2 storage operation. Magnetic resonance imaging (MRI) technique was used to observe pore-scale events in drainage process. After the injection of 3-5PV CO 2 , saturation of CO 2 keeps constant indicating that the rest part remains inaccessible. The CO 2 saturation at the last time for 8 MPa is higher than 6 MPa. Residual saturation and breakthrough time of different injection rate displacement procedures are different. The packed porous media is not perfectly homogeneous, so the CO 2 run through the high permeability regions vertically in a short period. With CO 2 injection, the brine saturation decreased gradually from the inlet of the bead-pack core, and the MRI image turned into dark gradually. The CO 2 front proceeding in the porous media could be measured clearly, we can find CO 2 “channeling” phenomena obviously in the case of gaseous CO2 displacement due to the difference of fluid viscosities and densities, and it can be seen from the profiles of 76 and 80 min. This phenomenon causes premature breakthrough of the CO 2 to occur, thereby reducing the displacement efficiency of the water. And yet, the piston-like displacement occurred in the supercritical CO 2 drainage experiment, due to the viscosity of supercritical CO 2 is higher than gaseous CO 2 . According to capillary number definition, the Darcy velocity U keep invariable with constant CO 2 flow rate, and the non-wetting phase (CO 2 ) viscosity increase with the injection pressure increase. In other words, the displacement process capillary number of 8 MPa is higher than 6 MPa. The sweep efficiency in 8 MPa is slightly higher compared to the CO 2 injection in 6 MPa. Therefore, supercritical CO 2 displacement process is more practical than gaseous CO 2 displacement process. The sweep efficiency will decrease for higher capillary number. At a small CO 2 injection rate, the breakthrough time is long. A longer break through time resulted higher sweep efficiency. The CO 2 flooding increases the displacement efficiency by raising the capillary number due to the relatively low interfacial tension values between the brine and the injected CO 2 . At high injection rate, especially 0.8 ml/min, the MRI image near the outlet region remain at high signal intensity in a relatively long time, indicating that the CO 2 -brine distribution does not change, since the displacement is steady. The sweep efficiency decreases as the injection flow rate increase, but the decrease extent reduces gradually. This means there is a critical capillary number for CO 2 sequestration, which results in minimum sweep efficiency. In future experimental work, we will go into more detail about the critical capillary number. Within the capillary number scope of 10 -9 to10 -10 , higher capillary number will decrease the CO 2 sweep efficiency. [ABSTRACT FROM AUTHOR]

A clear understanding of dynamic water flushing on laboratory scale is useful for the effectiveness and safety of CO 2 geological storage. The objective of this study was to investigate the effect of water flushing on CO 2 concentration including displacement and the dissolution. The high-resolution Magnetic Resonance Imaging (MRI) technique was used to visualize the process. The core sample was packed with glass beads under the temperature and pressure of 40 and 8 MPa, corroding to the depth of 800 m. The CO 2 unsaturated brine was injected upward into the supercritical CO 2 saturated sample with flow rate of 0.03 mL /min, to imitate the water flushing. The transient intensity in MRI image during the water flushing was observed, reflecting the transition from displacement to dissolution in the porous media. The concentration distribution along the porous media was inhomogeneous. The CO 2 concentration declined along the porous media with injected pore volume. [ABSTRACT FROM AUTHOR]

Owing to the complexity of geological formation, a detailed understanding of all transportation phenomenon of CO 2 /water in porous media occurring in CGS is not yet gained. Heterogeneity in wettability and pore structure exists in mostly natural geological formation which has been proof that gives strong effects on porous media flow. Since macroscopic transportation phenomenon in porous media are always determined by pore-scale properties, investigation on heterogeneity at pore-scale gives the most fundamental influence mechanisms of heterogeneity in wettability and pore structure. In this study, we reported a pore-scale study on the influence of heterogeneity in wettability and pore structure in vertical CO 2 /water displacement experiments using a micro-CT machine. Two stratified sand packs, BZ06+BZ02, quarz+dolomite, were employed in displacement experiments. The experiment results indicate that, CO 2 saturation pattern shows a big difference between dolomite layer and quartz layer, CO 2 enters more pore spaces and owns higher CO 2 saturation in dolomite layer than quartz layer in drainage. While in glass beads pack, it is noticeable that the capillary barrier of BZ02 layer significantly affects CO 2 percolation process. CO 2 occupied little void volume of BZ02 porous matrix. In imbibition, residual CO 2 was mainly trapped in more wetting quartz layer in quartz+dolomite pack, and more compact layer in BZ06+BZ02 pack. [ABSTRACT FROM AUTHOR]

A clear understanding of two-phase fluid flow properties in porous media is of importance to CO 2 geological storage. The study visually measured the immiscible and miscible displacement of water by CO 2 using MRI (magnetic resonance imaging), and investigated the factor influencing the displacement process in porous media which were filled with quartz glass beads. For immiscible displacement at slow flow rates, the MR signal intensity of images increased because of CO 2 dissolution; before the dissolution phenomenon became inconspicuous at flow rate of 0.8 mL min − 1 . For miscible displacement, the MR signal intensity decreased gradually independent of flow rates, because supercritical CO 2 and water became miscible in the beginning of CO 2 injection. CO 2 channeling or fingering phenomena were more obviously observed with lower permeable porous media. Capillary force decreases with increasing particle size, which would increase permeability and allow CO 2 and water to invade into small pore spaces more easily. The study also showed CO 2 flow patterns were dominated by dimensionless capillary number, changing from capillary finger to stable flow. The relative permeability curve was calculated using Brooks-Corey model, while the results showed the relative permeability of CO 2 slightly decreases with the increase of capillary number. [ABSTRACT FROM AUTHOR]

Understanding the physical trapping mechanisms is important to design successful CO2 storage projects. Among major trapping mechanism, the dissolution trapping is mainly influenced by the mass transfer between CO2 and brine interface. A typical dimensionless number, the Sherwood number, is predicted as empirical formulas with the CO2 volume fraction and the Reynolds number. Experiments of brine imbibition into pores which are occupied by CO2 are performed with different Re and injection direction. The most active mass transfer region are consist of relative high Re and high CO2 volume fraction according to the fitting results, and the Sh decrease intensely when Re decrease, especially when Re is below 0.1. Also the descending CO2 volume fraction have relative slight impact on Sh , inducing a probably decline of values. Thus for brine in aquifers a higher migration velocity when imbibition process will accelerate the dissolution process and be benefit to the safety of reservoir. [ABSTRACT FROM AUTHOR]