Modeling of CO2 storage as hydrate in vacated natural gas hydrate formation

Holding CO₂ at massive scale in enclathrated solid matter called hydrate can be perceived as one of the most reliable method for CO₂ storage in subsurface geological environment. In this study, a dynamically coupled mass, momentum, and heat transfer mathematical model is developed, which elaborates uneven behavior of CO₂ flowing into porous medium in space and time domain and converting itself into hydrates. The combined numerical model solution methodology by explicit finite difference iteration method is provided and through coupling the mass, momentum, and heat conservation relations, an integrated model can be presented to investigate the CO₂ hydrate growth within P-T equilibrium conditions. The article results illustrate that pressure distribution in hydrate formation becomes stable at initial phase of hydrate nucleation process, but formation temperature is unable to maintain its stability and varies during CO₂ injection and hydrate nucleation process. The hydrate growth rate increases by increasing injection pressure from 15 MPa to 16 and 17 MPa in 500-m-long formation, and it also expands overall hydrate-covered length from 200 m to 280 m and 320 m, respectively, in 1 month of hydrate growth period. Injection pressure conditions and hydrate growth rate affect other parameters like CO₂ velocity, CO₂ permeability, CO₂ density, and CO₂ and H₂O saturation. In order to enhance hydrate growth rate and expand hydrate-covered length, injection temperature is reduced from 282 K to 280 K, but it did not give satisfactory outcomes. In addition, hydrate growth termination and restoration effect is also witnessed due to temperature variations.     

Energy consumption estimation for greenhouse gas separation processes by clathrate hydrate formation

The process energy consumption was estimated for gas separation processes by the formation of clathrate hydrates. The separation process is based on the equilibrium partition of the components between the gaseous phase and the hydrate phase. The separation and capturing processes of greenhouse gases were examined in this study. The target components were hydrofluorocarbon (HFC-134a) from air, sulfur hexafluoride (SF₆) from nitrogen, and CO₂ from flue gas. Since these greenhouse gases would form hydrates under much lower pressure and higher temperature conditions than the accompanying components, the effective capturing of the greenhouse gases could be achieved by using hydrate formation. A model separation process for each gaseous mixture was designed from the basis of thermodynamics, and the process energy consumption was estimated. The obtained results were then compared with those for conventional separation processes such as liquefaction separation processes. For the recovery of SF₆, the hydrate process is preferable to liquefaction process in terms of energy consumption. On the other hand, the liquefaction process consumes less energy than the hydrate process for the recovery of HFC-134a. The capturing of CO₂ by the hydrate process from a flue gas will consume a considerable amount of energy; mainly due to the extremely high pressure conditions required for hydrate formation. The influences of the operation conditions on the heat of hydrate formation were elucidated by sensitivity analysis. The hydrate processes for separating these greenhouse gases were evaluated in terms of reduction of global warming potential (GWP).     

Effect of contaminants from flue gas on CO2 sequestration in saline formation

Deep saline aquifers are reported to have the largest estimated capacity for CO₂ sequestration. Most geochemical studies on CO₂ storage in saline formations are focused on the interactions of pure CO₂ and do not consider the potential impacts of contaminants such as SO₂ found in typical post‐composition flue gas streams. This paper reports on results of a combined CO₂–co‐contaminant–brine–rock experimental and a simple modeling study of the potential impact of flue gas contaminants on saline formations. Chemical reactions of the sandstone from Mount Simon formation exposed to CO₂ mixed with other gas species under sequestration conditions were studied (i.e. solid material — representative Mount Simon sandstone; liquid — synthetic Illinois Basin brine; T and P — 50 °C, 110 bar; gas composition — 1% SO₂, 4% O₂, 95% CO₂). The experimental study indicates that the co‐injection of 1% SO₂ would lead to substantially reduced brine pH due to the formation of sulfuric acid and the formation of bassanite (major) and anhydrites. Preliminary equilibrium computational modeling yielded similar results. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetic measurements and in situ Raman spectroscopy study of the formation of TBAF semi-hydrates with hydrogen and carbon dioxide

The kinetics of formation of semi-clathrate hydrates of tetra n-butyl ammonium fluoride (TBAF) with hydrogen (H₂) and carbon dioxide (CO₂) were studied in order to elucidate their potential for H₂ storage as well as for CO₂ sequestration. The influence of pressure, TBAF concentration (1.8 mol% and 3.4 mol%) and formation method (T-cycle method and T-constant method) on the hydrate nucleation, hydrate growth and the amount of gas uptake were determined. The results showed that the kinetics of formation of H₂–TBAF semi-hydrates is favored at high pressures and TBAF concentrations. The TBAF concentration did not display a large influence on the kinetics of formation of CO₂–TBAF semi-hydrates and pressure only showed a major influence on the formation rate. Instead, the induction time and the amount of CO₂ consumed were favored at low temperatures. Additionally, in situ Raman spectroscopy was used to confirm the gas uptake in the hydrate structure and to observe structural changes.     

Hydrate-based removal of carbon dioxide and hydrogen sulphide from biogas mixtures: Experimental investigation and energy evaluations

This paper presents an experimental study on the application of gas hydrate technology to biogas upgrading. Since CH₄, CO₂ and H₂S form hydrates at quite different thermodynamic conditions, the capture of CO₂ and H₂S by means of gas hydrate crystallization appears to be a viable technological alternative for their removal from biogas streams. Nevertheless, hydrate-based biogas upgrading has been poorly investigated. Works found in literature are mainly at a laboratory scale and concern with thermodynamic and kinetic fundamental studies. The experimental campaign was carried out with an up-scaled apparatus, in which hydrates are produced in a rapid manner, with hydrate formation times of few minutes. Two types of mixtures were used: a CH₄/CO₂ mixture and a CH₄/CO₂/H₂S mixture. The objective of the investigation is to evaluate the selectivity and the separation efficiency of the process and the role of hydrogen sulphide in the hydrate equilibrium. Results show that H₂S can be captured along with CO₂ in the same process. The maximum value of the separation factor, defined as the ratio between the number of moles of CO₂ and the number of moles of CH₄ removed from the gas phase, is 11. In the gas phase, a reduction of CO₂ of 24.5% in volume is achievable in 30 min.Energy costs of a real 30-min separation process, carried out in the experimental campaign, are evaluated and compared with those obtained from theoretical calculations. Some aspects for technology improvement are discussed.     

Hydrate-based separation of the CO2 + H2 mixtures. Phase equilibria with isopropanol aqueous solutions and hydrogen solubility in CO2 hydrate

The gas hydrates' ability to preferentially bind one of the components of a gas mixture into a hydrate state makes it possible to consider hydrate-based technology as promising for the separation of gas mixtures. When a hydrate is obtained from a gas mixture, mixed hydrates with a complex composition inevitably occur. Issue of their composition determination stays apart. This a rather difficult task, which is complicated by the dissolution of small molecules such as hydrogen in the hydrate phase. This, in turn, impedes the analysis of the data obtained. In this work, the solubility of hydrogen in carbon dioxide hydrate in the range of 269.7–275.7 K and at partial H₂ pressure up to 4.5 MPa was experimentally determined. Hydrate composition was found to be CO₂·(0.01X)H₂·6.5H₂O at H₂ pressure of X MPa. The equilibrium conditions of hydrates formation in the systems of H₂O – CO₂ – H₂ and H₂O – 2-propanol – CO₂ – H₂ were also determined in a wide range of hydrogen concentrations. Hydrogen seems to be an indifferent diluent gas regarding CO₂ hydrate equilibrium pressure. The compositions of the equilibrium phases have been determined as well. It was shown that isopropanol does not form a double hydrate with СО₂, only sI СО₂ hydrate occurred in the studied systems. The obtained dependencies will be useful in analyzing the process of СО₂ + Н₂ gas mixtures separation by the hydrate-based method.     

热激励的CO_2置换CH_4水合物的实验研究

CO_2置换CH_4水合物具有在开采天然气水合物的同时储藏CO_2的功能.天然气水合物因其可燃烧、燃烧后污染小、储量巨大等特点被认为是未来最有可能的能源替代品,但CO_2置换天然气水合物存在反应周期长、置换速率低的缺点.提出了一种借助CO_2水合物生成热量激励CH_4水合物分解的方法,在低温、高压的纯水体系中,研究了温度为275.15 K,置换压力分别为2.3、2.5、2.8、3.0 MPa时有热激励和无热激励两种置换反应的区别.研究结果表明,有热激励的置换反应,由于提供了额外的热量,使CH_4水合物更易分解,从而加速了置换反应的发生,提高了置换速率.     

Latest progress in numerical simulations on multiphase flow and thermodynamics in production of natural gas from gas hydrate reservoir

Natural gas hydrates are promising potential alternative energy resources. Some studies on the multiphase flow and thermodynamics have been conducted to investigate the feasibility of gas production from hydrate dissociation. The methods for natural gas production are analyzed and several models describing the dissociation process are listed and compared. Two prevailing models, one for depressurization and the other for thermal stimulation, are discussed in detail. A comprehensive numerical method considering the multiphase flow and thermodynamics of gas production from various hydratebearing reservoirs is required to better understand the dissociation process of natural gas hydrate, which would be of great benefit to its future exploration and exploitation.     

Effect of Nanobubble Evolution on Hydrate Process: A Review

As a huge reserve for potential energy, natural gas hydrates(NGHs) are attracting increasingly extra attentions, and a series of researches on gas recovery from NGHs sediments have been carried out. But the slow formation and dissociation kinetics of NGHs is a major bottleneck in the applications of NGHs technology. Previous studies have shown that nanobubbles, which formed from melt hydrates, have significant promotion effects on dissociation and reformation dynamics of gas hydrates. Nanobubbles can persist for a long time in liquids, disaccording with the standpoint of classical thermodynamic theories, thus they can participate in the hydrate process. Based on different types of hydrate systems(gas + water, gas +water +inhibitors/promoters, gas + water + hydrophilic/hydrophobic surface), the effects of nanobubble evolution on nucleation, dissociation, reformation process and "memory effect" of gas hydrates are discussed in this paper. Researches on the nanobubbles in hydrate process are also summarized and prospected in this study.     

The fate of CO2 hydrate released in the ocean

Disposal of anthropogenic CO₂ in the ocean has been considered as a method to counteract global warming. A desirable method of the ocean disposal is to convert the less dense liquefied CO₂ into denser CO₂ hydrate via a submerged hydrate crystallizer at a depth <500 m. The fate of CO₂ hydrate in the ocean has been investigated. It is shown in this study that hydrate particles released in the ocean are physicochemically unstable; however, hydrate decomposition occurs only as a surface phenomenon. Because CO₂ hydrate is denser than seawater, hydrate particles will sink in the ocean. During the descending process, the hydrate particles dissolve gradually in seawater owing to decomposition occurring continuously at surfaces of hydrate particles. This dissolution fate of CO₂ hydrate in the ocean is significantly different from the previous prediction that the disposed CO₂ hydrate would exist as a long‐lasting entity in the ocean. Copyright © 1999 John Wiley & Sons, Ltd.     

Hybrid hydrate processes for CO2/H2 mixture purification: A techno-economic analysis

In this work, hydrate based separation technique was combined with membrane separation and amine-absorption separation technologies to design hybrid processes for separation of CO₂/H₂ mixture. Hybrid processes are designed in the presence of different types of hydrate promoters. The conceptual processes have been developed using Aspen HYSYS. Proposed processes were simulated at different flow rates for the feed stream. A comprehensive cost model was developed for economic analysis of novel processes proposed in this study. Based on the results from process simulation and equipment sizing, the amount of total energy consumption, fixed cost, variable cost, and total cost were calculated per unit weight of captured CO₂ for various flow rates of feed stream and in the presence of different hydrate promoters. Results showed that combination of hydrate formation separation technique with membrane separation technology results in a CO₂ capture process with lowest energy consumption and total cost per unit weight of captured CO₂. As split fraction and heat of hydrate formation increases, the share of hydrate formation section in total energy consumption increases. When TBAB is applied as hydrate promoter, due to its higher hydrate separation efficiency, more amount of CO₂ is captured in hydrate formation section and consequently the total cost for process decreases considerably. Hybrid hydrate-membrane process in the presence of TBAB as hydrate promoter with 29.47 US$/ton CO₂ total cost is the best scheme for hybrid hydrate CO₂ capture process. Total cost for this process is lower than total cost for single MDEA-based absorption process as the mature technology for CO₂ capture.     

Gas hydrate formation process for pre-combustion capture of carbon dioxide

In this study, gas hydrate from CO₂/H₂ gas mixtures with the addition of tetrahydrofuran (THF) was formed in a semi-batch stirred vessel at various pressures and temperatures to investigate the CO₂ separation/recovery properties. This mixture is of interest to CO₂ separation and recovery from Integrated Gasification Combine Cycle (IGCC) power plants. During hydrate formation the gas uptake was determined and composition changes in the gas phase were obtained by gas chromatography. The impact of THF on hydrate formation from the CO₂/H₂ was observed. The addition of THF significantly reduced the equilibrium formation conditions. 1.0 mol% THF was found to be the optimum concentration for CO₂ capture based on kinetic experiments. The present study illustrates the concept and provides thermodynamic and kinetic data for the separation/recovery of CO₂ (pre-combustion capture) from a fuel gas (CO₂/H₂) mixture.     

“CH4-CO2”置换法开采天然气水合物

天然气水合物作为一种储量巨大的清洁能源,其开采价值已引起越来越多的关注。当前天然气水合物开采技术仍不足以商业化应用,还需进一步的实验研究进行理论支撑。二氧化碳置换开采天然气水合物被认为是能同时实现天然气水合物开采与二氧化碳减排、封存的双赢技术,近年来得到了较广泛的研究。置换过程中,混合天然气水合物的热力学和结构性质是预测含水合物沉积物中的热流和水合物解离所需的热量以及评估水合物储层的CO₂储存能力的关键因素。本综述在调研国内外天然气水合物开采技术研究现状的基础上,围绕CO₂置换开采天然气水合物的热力学特性、微观机理与置换效率等,总结了各研究取得的成果,针对置换研究中存在的问题进行了分析,认为当前置换法开采天然气水合物最关键难点在于提高置换效率,而解决该问题的根本在于从热力学和动力学角度弄清楚置换反应的微观机理及控制性因素,明确置换机理,从而在未来的研究有的放矢。     

Kinetics measurements and in situ Raman spectroscopy of formation of hydrogen–tetrabutylammonium bromide semi-hydrates

The kinetics of formation of H₂–TBAB semi-clathrate hydrates was studied in this work in order to elucidate their potential for H₂ storage. The influence of pressure (5–16 MPa), TBAB concentration (2.6 mol% and 3.7 mol%) and formation method (T-cycle method and T-constant method) on the hydrate nucleation, hydrate growth and H₂ storage capacity was determined. The results showed that kinetics is favored at higher pressures and solute concentrations. Additionally, the hydrate phase formation and dissociation was study for a solution of 2.6 mol% of TBAB in situ by using the Raman spectroscopy technique. The inclusion of H₂ in the semi-hydrate phase was confirmed. The results showed the importance of H₂ mass transfer on the storage capacity of the H₂–TBAB semi-hydrates.     

The CO2 storage capacity evaluation: Methodology and determination of key factors

It is a win–win technology to inject CO₂ into the oil or gas reservoirs. Because it can reduce the greenhouse gas emission and enhance oil recovery. In some oil or gas reservoirs, the reservoir water and the strong heterogeneity make the CO₂ storage capacity difficult to be determined. In this research, the CO₂ storage evaluation method is introduced. This method considers the CO₂ displacement efficiency, the CO₂ sweep efficiency, the CO₂ dissolution in oil and gas and the CO₂ displacement mechanism. The key factors in this evaluation method are determined by the reservoir simulation method, the thermodynamic theories and the statistical analysis methods separately. At last, the CO₂ storage capacity evaluation system is built. This system can be used to evaluate the CO₂ storage capacity fast and reliably and it worth to be promoted in the area of CO₂ storage.     

An experimental investigation into the effects of zeolites on the formation of methane hydrates

Methane hydrate is an ice‐like nonstoichiometric compound that forms when methane reacts with water at high pressures and low temperatures. It has a lot of practical applications such as separation processes, natural gas storage transportation, and carbon dioxide sequestration. Especially, the industrial use of hydrates requires large amounts of gas to be formed quickly into hydrates. Porous media significantly influence the rate of hydrate formation by reducing the chemical barrier, where zeolites are microporous minerals. This paper deals with natural and synthetic (5A and 13A) zeolites for hydrate formation and gas storage capacity. The results show that methane hydrates are formed much faster in the three zeolite solutions tested compared with their formation in distilled water at low subcooling temperatures (<7 K). It was also observed that the gas consumption was the greatest in the 0.01 wt.% zeolite 13X solution of distilled water. Its gas consumption was 5.1 times that of distilled water at 0.5 K subcooling. Zeolite 13X demonstrated its effectiveness in enhancing and expediting methane hydrate formation. Copyright © 2014 John Wiley & Sons, Ltd.     

Preliminary report on the commercial viability of gas production from natural gas hydrates

Economic studies on simulated gas hydrate reservoirs have been compiled to estimate the price of natural gas that may lead to economically viable production from the most promising gas hydrate accumulations. As a first estimate, $CDN₂₀₀₅ 12/Mscf is the lowest gas price that would allow economically viable production from gas hydrates in the absence of associated free gas, while an underlying gas deposit will reduce the viability price estimate to $CDN₂₀₀₅ 7.50/Mscf. Results from a recent analysis of the simulated production of natural gas from marine hydrate deposits are also considered in this report; on an IROR basis, it is $US₂₀₀₈ 3.50–4.00/Mscf more expensive to produce marine hydrates than conventional marine gas assuming the existence of sufficiently large marine hydrate accumulations. While these prices represent the best available estimates, the economic evaluation of a specific project is highly dependent on the producibility of the target zone, the amount of gas in place, the associated geologic and depositional environment, existing pipeline infrastructure, and local tariffs and taxes.     

Characteristics and factors of gas-water relative permeability in volcanic gas reservoir

Volcanic gas reservoirs have features of strong heterogeneity and difficult development. The laboratory experiment results show that the shapes of gas-water relative permeability curves and the values of feature points are related to the experimental conditions. In the same core, the higher the temperature, the pressure, or the content of CO₂ is, the lower the irreducible water saturation is, and the faster the gas relative permeability rises, the better the seepage of gas-water is. During the process of gas driving water, the fractures have significant influences on the bound water saturation and the percolation characteristics of gas-water.     

水合物藏定质量流量转定井底流压开采规律研究

天然气水合物资源潜力巨大，降压法是水合物资源开采最有前景的方法。本文提出了定质量流量转定井底流压生产的降压开采模式，使用数值模拟方法研究了此模式下水合物藏的气水生产动态和物理场的变化规律。结果表明：（1）定质量流量生产阶段的产气速率约为定井底流压生产阶段的3倍；对于分解气速率，定质量流量生产阶段与定井底流压生产阶段相当，但在定井底流压生产阶段后期分解气速率上升幅度近200%；产水速率在定质量流量生产阶段和定井底流压生产阶段整体较为稳定。（2）储层的压力场、温度场和水合物饱和度场的变化有相似的规律，随时间增加，低压、低温和低水合物饱和度范围均以井筒为中心不断扩大。（3）本文降压生产模式的总体开发效果介于单一的定质量流量生产和定井底流压生产之间，具有较高的产量，且能够较好地保持地层能量。     

Ab initio mechanistic insights into the stability,diffusion and storage capacity of sI clathrate hydrate containing hydrogen

Gas hydrates are non-conventional materials offering great potential in capturing, storage, and sequestration of different gases. The weak van der Waals interactions between a gas molecule and the pore walls stabilize these non-stoichiometric structures. The present article reports an ab initio improved van der Waals density functional (vdW-DF2) study devoted to the interactions associated with H₂, CH₄, and CO₂ adsorption in sI clathrate hydrate. The study provides the clathrate stability, diffusion, and energy storage of possible mixed gas occupancy in sI cages in the presence of H₂. The results also provided the hydrogen energy landscapes and the estimated diffusion activation energy barriers to the large and small cage to be 0.181 and 0.685 eV, respectively. In addition, the results showed that the presence of CH₄ or CO₂ could enhance the storage capacity, thermodynamic stability, and hydrogen diffusion in sI clathrates. The volumetric storage, gravimetric storage, and molecular hydrogen content in H₂–CH₄ binary sI clathrate are calculated to be 2.0 kW h/kg, and 1.8 kW h/L, and 5.0 wt%, respectively. These results are comparable to DOE targets of hydrogen storage.