【作者】 张新军；

【导师】 陈月明；

【作者基本信息】 中国石油大学 ， 油气田开发工程， 2008， 博士

【摘要】 天然气水合物以其巨大的资源量成为能源开发的热点。在油气资源日趋紧张的形势下,合理开发天然气水合物藏,可以缓解目前社会所面临的能源危机。世界各国政府都高度重视对天然气水合物开采的基础研究,降压法是开发天然气水合物藏的一种重要的方法。在天然气水合物的降压开采过程中,天然气水合物在多孔介质中的形成与分解对储层参数(如饱和度、渗透率、孔隙度、声波波速、岩电阻率)的影响,一些重要的开发参数(如水合物饱和度)的测试和定量解释,地层水中的盐浓度、水合物饱和度的分布对水合物藏的开发动态的影响,相应的数学模型和数值模拟研究等问题是天然气水合物开发领域的前沿课题。目前,国内外对这方面的研究尚十分欠缺。本研究从室内实验、理论研究和数值模拟三个方面出发,对以上问题进行了研究。研究分两条主线:一是实验研究,主要进行天然气水合物实验设备的研制、储层物性测量和开采实验;二是数值模拟研究,包括天然气水合物开采数学和数值模型的建立、相应计算程序的编制和数值模拟。在充分调研的基础上,设计了天然气水合物储层物性测量及开采实验系统和一维天然气水合物电阻率测量实验装置,专门用于水合物储层参数变化规律实验研究和水合物储层电阻率测量;建立了含盐富水相天然气水合物储层开采数学模型,该模型可以描述三相(气、液、水合物)八组分水合物储层开采的多相非等温渗流。研究得出了如下结论:(1)实验验证了储层渗透率和孔隙度随水合物饱和度的变化规律,提出了新的描述储层渗透率和水合物饱和度之间关系的指数型关系式;验证了水溶液中盐组分的存在可引起甲烷水合物相平衡曲线向左移动,回归了新的盐浓度与过冷度关系的经验公式。(2)提出描述储层声波波速与水合物饱和度的修正的威利方程,可以解释储层的水合物饱和度。(3)提出了适用于含盐富水相的天然气水合物体系的饱和度电阻率解释模型,并进行了一维天然气水合物电阻率测量实验,利用水合物饱和度电阻率解释模型可以确定水合物饱和度分布。(4)提出天然气水合物加热分解的动力学理论假设,并分析了天然气水合物降压与加热分解的综合过程,使建立的天然气水合物开采数学模型可以描述降压和加热开采过程。在所建立的含盐富水相天然气水合物储层开采数学模型中,包括组分质量守恒方程、能量守恒方程以及气组分、盐和抑制剂的输运方程、天然气水合物的分解动力学方程。该模型较全面地反映了含盐富水相天然气水合物储层开采的作用机理。(5)应用有限差分法对含盐富水相天然气水合物储层开采数学模型进行了离散。数学模型的求解方法采用变量逐次求解的方法,即在一个时间步长之内依次求解压力、饱和度、温度、气相组分分数、盐或抑制剂的浓度分布。实践表明,该计算方法既满足了数值计算的需求,又使得处理过程变得相对简单。(6)利用所编制的含盐富水相天然气水合物藏储层开采数值模拟程序,对一维甲烷水合物降压开采实验进行了数值模拟。讨论了水合物降压开采的影响因素。结果表明,水合物饱和度分布、储层水溶液的盐浓度等因素对水合物降压开发动态具有明显的影响。更多还原

【Abstract】 Natural gas hydrate (NGH) is regarded as the development focus of energy for its large reserve. With the severe situation of oil and gas resources being less and less, the energy crisis in current society can be alleviated by the rational development of NGH reservoir. The governments all around the world pay high attention to the fundamental research of NGH exploitation. Depressurization is an important method of developing NGH reservoir. The forward topics on the NGH development include: the impact of the formation and decomposition of NGH in porous media during depressurizing development on the reservoir parameters (such as saturation, permeability, porosity, acoustic velocity, rock resistivity); the measurement and quantitative interpretation of some important development parameters (such as the NGH saturation); the impact of the distribution of salt concentration of reservoir water and the NGH saturation on the development performance, and the study on mathematical model and numerical simulation. So far, there is little research on the subject at home and abroad.These problems are studied through laboratory experiment, theoretical research and numerical simulation in this paper. There are two main line: one is experimental research, including the development of NGH experimental equipment, the measurement of NGH reservoir physical properties and the experiment of NGH development, the other is numerical simulation study, including the construction of mathematical and numerical model, the programming of corresponding software and the numerical simulation. On the basic of full investigation two sets of devices for hydrate experiment are designed: one for measuring the physical properties and developing the NGH reservoir, the other for measuring the one-dimension resistivity of NGH. These devices are specially used to study the variations of reservoir parameters and measure the resistivity of hydrate reservoir. A three-phase (gas, water and hydrate), eight-component mathematical model for NGH reservoir of the salt-containing, water-rich phase is presented, which can describe multiphase, non-isothermal seepage.The conclusions are as follows:(1) The law of reservoir permeability and porosity with hydrate saturation is testified. Exponential-type formula, a new formula for describing the relationship between the permeability and saturation is presented. The left shift of methane hydrate phase-equilibrium curve caused by salt component in the solution is testified, a new empirical formula between salt concentration and super-cooling degree is regressed.(2) The modified formula of Wyllie equation, which describes the relationship between acoustic velocity and hydrate saturation in the reservoir, can interpret the hydrate saturation.(3) Saturation resistivity interpretation model suitable for NGH system of salt-containing, water-rich phase is proposed, which is suitable for resistivity log interpretation of saturation in the hydrate reservoir. One-dimensional measurement experiment of resistivity is carried out, and resistivity explanation model is used to obtain the distribution of hydrate saturation.(4) The kinetic hypothesis of NGH’s thermal decomposition is presented, and the integrated process of the depressurization and thermal decomposition is analyzed. Therefore, the mathematical model can be applied for the depressurizing and heating process. The mathematical model mentioned above includes mass conservation equation of the components, energy conservation equation, transport equation of gas components, salt and inhibitor, and decomposition kinetic equation of NGH. The factors, such as temperature, components, phase equilibrium, are fully considered in the multiphase seepage model, so as to well describe the development mechanism of salt-containing, water rich phase NGH reservoir.(5) The mathematical model is discretized by finite difference method and solved by sequential solution method, which is to successively solve the pressure, saturation, temperature, mass fraction of gas phase, the distribution of salt or inhibitor in a time step. It is proved that this method not only meets the demand of numerical calculation, but also simplifies the processing procedure.(6) The self-made program is used in the one-dimensional depressurization numerical simulation of methane hydrate and the influencing factors of depressurization are analyzed. The results suggest that the factors, such as distribution of hydrate saturation and salt concentration of reservoir solution, have a great effect on depressurized development performance of the hydrate.更多还原