Injection of liquid carbon dioxide into a reservoir partially saturated with methane hydrate

A mathematical model is proposed to describe methane–carbon dioxide replacement in gas hydrate by injecting liquid carbon dioxide into a porous medium initially saturated with methane and its hydrate. Self-similar solutions of the axisymmetric problems are constructed that describe the distribution of the main parameters of the reservoir. It is shown that there exist solutions according to which the process can occur both with and without boiling of carbon dioxide. Diagrams of the existence of each type of solution are constructed.     

Injection of carbon dioxide into a reservoir saturated with methane and water

This paper presents a mathematical model for the injection of carbon dioxide into a natural gas reservoir saturated with methane and water accompanied by the formation of carbon dioxide hydrate in an extended region. The dependence of the coordinates of the boundaries of the region of phase transitions on the pressure of the injected gas and the initial parameters of the reservoir are investigated. It is established that the velocity of the near boundary of the region of hydrate formation decreases with increasing water saturation and initial temperature of the reservoir and the velocity of the far boundary of the region of phase transitions increases with increasing pressure of the injected gas and reservoir permeability. It is shown that at high initial temperatures of the reservoir, a regime is possible in which replacement of methane by carbon dioxide without hydrate formation occurs at the far interface, and at the near interface, water is completely incorporated into gas hydrate.     

Thermodynamic Conditions of Formation of CO<Subscript>2</Subscript> Hydrate in Carbon Dioxide Injection into a Methane Hydrate Reservoir

The mechanism of replacement of methane by carbon dioxide in the hydrate in the process of CO₂ injection into a reservoir with formation of fronts of methane hydrate dissociation and carbon dioxide hydrate generation is investigated. It is found that such a replacement regime can be implemented in both low- and high-permeability reservoirs. It is shown that in the highintensity injection regime the heat flux from the well does not affect propagation of the fronts of methane hydrate dissociation and carbon dioxide hydrate generation. In this case the replacement regime is maintained by only the heat released at formation of carbon dioxide hydrate. An increase in the injection pressure may lead to suppression of methane hydrate dissociation and termination of the replacement reaction. The critical diagrams of existence of the regime of conversion of methane hydrate to carbon dioxide hydrate are constructed.     

Modeling of Gas Hydrate Formation Upon Injection of Carbon Dioxide Gas into A Natural Reservoir

This paper presents the results of numerical modeling of gas hydrate formation upon injection of carbon dioxide into a finite-length reservoir saturated with methane and water. It is shown that at different stages, hydrate formation can occur on both the frontal surface and in a reservoir region of finite length. The effects of pressure at the reservoir boundaries and the effects of the permeability and initial water saturation of the reservoir on the hydrate formation process were studied. The dependences of the time of the complete conversion of water into gas hydrate in the entire reservoir on the injection pressure and reservoir permeability were obtained.     

水合物沉积物力学性质的研究现状

天然气水合物(简称水合物)是一些具有相对较低分子质量的气体如甲烷,二氧化碳、氮气等在一定温度和压力条件下与水形成的内含笼形孔隙的冰状晶体.天然气水合物沉积物(简称水合物沉积物)是指蕴含水合物的砂、黏土以及混和土等土质的沉积物质.主要从现场调查、室内试验和理论模型分析3个方面对甲烷水合物沉积物力学性质的研究现状做了介绍.在现场调查方面着重介绍水合物沉积物原位和调查船上的物性试验,并对原位带孔压测量的圆锥静力触探试验在水合物沉积物力学性质现场调查中的应用前景进行了阐述;在室内试验方面主要介绍了原状和人工合成的水合物沉积物的三轴试验结果,测定弹性参数的声波测试试验结果,天然气和水的含量及沉积物特性对水合物沉积物强度影响的试验结果,以及与水合物开采有关的水合物分解对水合物沉积物强度影响的室内试验和结果;在理论模型方面着重介绍了目前经常采用的几个模型的特点及应用范围.最后提出了今后在水合物沉积物力学性质研究方面应开展的工作重点及发展方向.      

The Experimental and Numerical Studies on Gas Production from Hydrate Reservoir by Depressurization

A set of experimental system to study hydrate dissociation in porous media is built and some experiments on hydrate dissociation by depressurization are carried out. A mathematical model is developed to simulate the hydrate dissociation by depressurization in hydrate-bearing porous media. The model can be used to analyze the effects of the flow of multiphase fluids, the kinetic process and endothermic process of hydrate dissociation, ice-water phase equilibrium, the variation of permeability, convection and conduction on the hydrate dissociation, and gas and water productions. The numerical results agree well with the experimental results, which validate our mathematical model. For a 3-D hydrate reservoir of Class 3, the evolutions of pressure, temperature, and saturations are elucidated and the effects of some main parameters on gas and water rates are analyzed. Numerical results show that gas can be produced effectively from hydrate reservoir in the first stage of depressurization. Then, methods such as thermal stimulation or inhibitor injection should be considered due to the energy deficiency of formation energy. The numerical results for 3-D hydrate reservoir of Class 1 show that the overlying gas hydrate zone can apparently enhance gas rate and prolong life span of gas reservoir.     

CH4/CO2 混合气体爆燃特性研究进展

掌握甲烷与二氧化碳混合气体的爆燃特性对高含二氧化碳天然气的勘探、开发和利用具有安全保障作用,对涉及甲烷和二氧化碳的其他工业过程如煤炭气化、惰化、抑爆、泄爆等应急处置和安防设计具有指导价值。为推动相关学科的进步,分类回顾了甲烷与二氧化碳混合气体爆燃特性的实验和理论研究进展,涉及爆燃范围、爆燃压强、惰化等爆燃特性的实验研究以及爆燃范围领域的理论研究,系统分析和评价了各个研究领域取得的成果、存在的问题,并从提高实验数据的完整性、可比性和适用面,理论预测方法可靠性的评价方法与指标,理论预测方法的适用面从常温常压条件向更复杂的情形扩展3个方面展望了未来的研究重点。     

Processes of hydrate formation and dissolution behind a shock wave in a liquid containing gas bubbles (mixture of nitrogen and carbon dioxide)

The processes of dissolution and hydrate formation behind a moderate-amplitude shock wave in water containing gas bubbles (mixture of nitrogen and carbon dioxide) are studied in experiments with different initial static pressures in the medium and concentrations of carbon dioxide in bubbles. An increase in static pressure in the gas-liquid medium is demonstrated to enhance the influence of the non-reacting gas (nitrogen) on the processes of dissolution and hydrate formation. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 178–187, March–April, 2009.     

Adsorption and strain: The CO2-induced swelling of coal

Enhanced coal bed methane recovery (ECBM) consists in injecting carbon dioxide in coal bed methane reservoirs in order to facilitate the recovery of the methane. The injected carbon dioxide gets adsorbed at the surface of the coal pores, which causes the coal to swell. This swelling in confined conditions leads to a closure of the coal reservoir cleat system, which hinders further injection. In this work we provide a comprehensive framework to calculate the macroscopic strains induced by adsorption in a porous medium from the molecular level. Using a thermodynamic approach we extend the realm of poromechanics to surface energy and surface stress. We then focus on how the surface stress is modified by adsorption and on how to estimate adsorption behavior with molecular simulations. The developed framework is here applied to the specific case of the swelling of CO₂-injected coal, although it is relevant to any problem in which adsorption in a porous medium causes strains.     

Formation of hydrate in injection of liquid carbon dioxide into a reservoir saturated with methane andwater

Injection of liquid carbon dioxide into a depleted natural gas field is investigated. A mathematical model of the process which takes into account forming CO₂ hydrate and methane displacement is suggested. An asymptotic solution of the problem is found in the one-dimensional approximation. It is shown that three injection regimes can exist depending on the parameters. In the case of weak injection, liquid carbon dioxide boils up with formation of carbon-dioxide gas. The intense regime is characterized by formation of CO₂ hydrate or a mixture of CO₂ and CH₄ hydrates. Critical diagrams of the process which determine the parameter ranges of the corresponding regimes are plotted.     

Injection of A Hydrate-Forming Gas into A Snow Layer Saturated with the Same Gas

The problem of injection of a hydrate-forming gas (methane) into a snow layer whose pores are initially saturated with the same gas is solved. Self-similar solutions describing the temperature and pressure fields and the snow, hydrate, and gas distributions in the layer are constructed. It is shown that, depending on the initial thermobaric state of the snow–methane system and the rate of gas injection, three characteristic zones can be distinguished in the filtration region: a near zone, in which snow is completely converted into hydrate and, consequently, the hydrate layer is saturated with gas; an intermediate zone, in which gas, snow, and hydrate are in phase equilibrium; far zone filled with gas and snow. It is shown that the length of the heated zone decreases with increasing initial snow content in the layer and with decreasing injected gas pressure. It is also shown that the length of the region of hydrate formation increases with increasing permeability. It is noted that the heating of the intermediate zone occurs more rapidly.     

Numerical modeling of formation of a gas hydrate in a finite-length porous bed purged by a gas

The process of formation of a gas hydrate in a finite-length porous medium partially saturated with water, which is purged by a cold gas, is studied. The influence of the initial parameters of the porous medium and purging conditions on the evolution of hydrate saturation and temperature is examined.     

Effect of decomposition of a gas hydrate on the gas recovery from a reservoir containing hydrate and gas in the free state

The problem of gas recovery in the process of methane hydrate dissociation in a reservoir saturated with gas-hydrate mixture is considered. The mathematical model of hydrate decomposition into gas and water is generalized to include the negative temperature interval and takes ice formation into account. The solution of the problem is represented in the self-similar approximation. It is shown that there exists a transition hydrate decomposition regime in which water and ice are formed simultaneously. A comparative analysis of the recovery is carried out on the basis of relations derived for the masses of recovered gas in different hydrate dissociation regimes. It is shown that an anomalous increase in the recovered gas volumes is observed in the transition hydrate dissociation regime.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, 2005, pp. 132–142. Original Russian Text Copyright © 2005 by Tsypkin.     

Numerical investigation of the decomposition of gas hydrates coexisting with gas in natural reservoirs

The problem of methane hydrate decomposition in a reservoir saturated with a gas and hydrate mixture is investigated numerically. The results of the numerical simulation and an analytic solution obtained in the linear approximation are compared. It is shown that for high-permeability rocks the convective heat transfer in the near-well space of the reservoir predominates over the conductive transfer. This makes the use of intra-well heaters ineffective. It is found that an increase in the reservoir and well pressures and a decrease in the permeability suppress the formation of an extended hydrate dissociation region. Critical diagrams of existence of the frontal decomposition regime are constructed.     

Numerical simulation of transpiration cooling through porous material

Transpiration cooling using ceramic matrix composite materials is an innovative concept for cooling rocket thrust chambers. The coolant (air) is driven through the porous material by a pressure difference between the coolant reservoir and the turbulent hot gas flow. The effectiveness of such cooling strategies relies on a proper choice of the involved process parameters such as injection pressure, blowing ratios, and material structure parameters, to name only a few. In view of the limited experimental access to the subtle processes occurring at the interface between hot gas flow and porous medium, reliable and accurate simulations become an increasingly important design tool. In order to facilitate such numerical simulations for a carbon/carbon material mounted in the side wall of a hot gas channel that are able to capture a spatially varying interplay between the hot gas flow and the coolant at the interface, we formulate a model for the porous medium flow of Darcy–Forchheimer type. A finite‐element solver for the corresponding porous medium flow is presented and coupled with a finite‐volume solver for the compressible Reynolds‐averaged Navier–Stokes equations. The two‐dimensional and three‐dimensional results at Mach number Ma = 0.5 and hot gas temperature T_HG=540 K for different blowing ratios are compared with experimental data. Copyright © 2014 John Wiley & Sons, Ltd.     

Front Regime of Heat and Mass Transfer in a Gas Hydrate Reservoir under the Negative Temperature Conditions

The analytical self-similar solution to the nonlinear problem of the front regime of heatand- mass transfer in a gas hydrate reservoir under the negative temperature conditions is obtained. In the initial state the reservoir is assumed to be saturated with a heterogeneous gas hydrate–ice–gas mixture. In particular cases there may be no ice or/and gas. The ice and gas are formed behind the gas hydrate dissociation front. The calculations are presented for a stable hydrate–gas system. The critical curves are constructed in the well-pressure–reservoir-permeability plane. These curves separate the domains of the front regime and the regime of volume gas hydrate dissociation ahead of the front. The velocity of the gas hydrate dissociation front is investigated as a function of various problem parameters. The characteristic temperature and pressure distributions corresponding to various regimes on the diagram are investigated.     

CF3I和CO2抑制甲烷-空气爆炸实验研究

为了探究三氟碘甲烷CF₃I和二氧化碳CO₂复合使用对甲烷爆炸的抑制效果,采用容积为20 L的球形爆炸实验装置,研究了单独和复合使用三氟碘甲烷和二氧化碳对甲烷爆炸压力特性的影响。研究结果表明:添加三氟碘甲烷和二氧化碳后,甲烷爆炸极限范围逐渐缩小,且三氟碘甲烷对甲烷爆炸极限的影响更显著,当三氟碘甲烷和二氧化碳的体积分数分别达到5.5%和32.0%时,甲烷爆炸上下限重合,临界氧的体积分数分别为17.85%和12.50%。可见三氟碘甲烷对甲烷爆炸极限的影响机制与二氧化碳不同,并不是通过降氧为主而发挥抑制作用的。三氟碘甲烷对甲烷爆炸的抑制效果明显优于二氧化碳,对比体积分数为9.5%的甲烷爆炸最大爆炸压力和最大爆炸压力上升速率下降的比率,5.0%三氟碘甲烷的抑爆效果约是等量二氧化碳的6倍和5倍。二氧化碳掺混少量三氟碘甲烷后,抑爆效果大幅提升,掺混比例越,高效果越明显,且对抑制甲烷爆炸压力作用的提升更显著。三氟碘甲烷掺混体积分数大于等于1.0%时,二氧化碳单位增量导致甲烷最大爆炸压力下降的幅度有所增加。这说明三氟碘甲烷的加入具有改善抑爆效果和增强抑爆效率的双重作用。     

Formation of a gas hydrate due to injection of a cold gas into a porous reservoir partly saturated by water

Specific features of formation of gas hydrates due to injection of a gas into a porous medium initially filled by a gas and water are considered. Self-similar solutions of an axisymmetric problem, which describe the distributions of the basic parameters in the reservoir, are constructed. The existence of solutions is demonstrated, which predict gas hydrate formation both on the frontal surface and in the volume zone. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 137–150, May–June, 2008.     

初始压力对多孔介质中气体水合物生成的影响

利用自制的一维天然气水合物生成与开采模拟实验系统,实验研究多孔介质中天然气水合物生成时不同初始压力对生成量、生成时间的影响.分别用相同气水比注入、相同注气量不同注水量、相同注水量不同注气量三种方式来控制初始压力.结果表明:在砂粒粒径300μm～500μm,盐水质量浓度2%,系统温度为2℃、初始压力为5MPa～9MPa的条件下进行水合物的等容生成实验时,初始压力越大,生成的水合物量越多,水合物开始生成的时间越早;但初始压力越大,实验系统中水合物生成最终稳定所需的时间越长.本实验系统采用的三种不同的控制初始压力的方式都可以得到上述结果.由此,可以为今后室内进行天然气水合物的生成实验提供科学指导.     

The simulation of gas production from oceanic gas hydrate reservoir by the combination of ocean surface warm water flooding with depressurization

A new method is proposed to produce gas from oceanic gas hydrate reservoir by combining the ocean surface warm water flooding with depressurization which can efficiently utilize the synthetic effects of thermal, salt and depressurization on gas hydrate dissociation. The method has the advantage of high efficiency, low cost and enhanced safety. Based on the proposed conceptual method, the physical and mathematical models are established, in which the effects of the flow of multiphase fluid, the kinetic process of hydrate dissociation, the endothermic process of hydrate dissociation, ice-water phase equilibrium, salt inhibition, dispersion, convection and conduction on the hydrate dissociation and gas and water production are considered. The gas and water rates, formation pressure for the combination method are compared with that of the single depressurization, which is referred to the method in which only depressurization is used. The results show that the combination method can remedy the deficiency of individual producing methods. It has the advantage of longer stable period of high gas rate than the single depressurization. It can also reduce the geologic hazard caused by the formation deformation due to the maintaining of the formation pressure by injected ocean warm water.