【作者】 刘力；

【导师】 蒋国盛； 宁伏龙；

【作者基本信息】 中国地质大学 ， 地质工程， 2013， 博士

【摘要】 天然气水合物(Natural Gas Hydrate,简称Gas Hydrate)是由水分子和天然气气体分子组成的具有笼状结构的似冰雪状结晶化合物,属气体水合物范畴。因其外观像冰且遇火即可燃烧,所以又被称作“可燃冰”、“固体瓦斯”或“气冰”。其中,天然气气体的成分包括烃类(CH4、C2H6、C3H8、C4H10等同系物)和非烃类气体(CO2、N2、H2S等),这些气体赋存于水分子笼形格架内。由于形成天然气水合物的主要气体成分是甲烷,故通常将甲烷分子含量超过99%的天然气水合物称为甲烷水合物(Methane Hydrate)。天然气水合物是一种亚稳态物质,只能在低温、高压条件下稳定存在,自然界中主要存在于海底陆架沉积物和极地永冻层下,并且广泛分布于大陆、岛屿的斜坡地带、活动和被动大陆边缘的隆起处、极地大陆架以及海洋和一些内陆湖的深水环境,甚至外太空也可发现其踪迹。自从上世纪60年代和80年代分别在永久冻土带和海洋区域发现天然气水合物以来,其在资源、环境和全球变化中的重要意义引起了各国政府、各大油气公司和各类学术研究机构的极大关注,成为当前能源和地球科学研究的一大热点。其研究涉及的领域已从最初的天然气管道的流动保障扩展到资源潜力、钻井安全、地质灾害、碳循环与气候变化等。天然气水合物研究水平已在某种程度上反应了一个国家的综合科技实力和可持续发展潜力。研究表明,未来针对水合物研究的关键任务是将其由基础研究和发展规划向全面的水合物开采等应用性研究转变。由于已成功实施了若干水合物研究项目,并具有近海岸和阿拉斯加永久冻土带富存水合物的先天优势,美国成为水合物研究领域的引领者之一,其制定出2015年前对阿拉斯加北坡冻土区水合物开采、2025年前实现对海洋地区水合物开采的计划。此外,日本、加拿大、德国、英国、俄罗斯、挪威、韩国、印度、中国等国家都开展了大量的水合物研究工作,其中日本也制定了2018年实现水合物商业开采的计划,西班牙、尼日利亚、智利、哥伦比亚、新西兰和秘鲁等也都对水合物研究表现出了浓厚的兴趣。初步勘探和研究表明,我国水合物储量较为丰富,开展水合物相关研究对满足我国能源需求具有重要战略意义,我国已把水合物开发列入“国家中长期(2006-2020年)科技发展规划”中。与宏观政策相适应,我国有关水合物调查研究、技术体系、实验模拟及其与环境、气候有关的科研活动也有较大幅度增加。勘探工作是进行水合物储层物性、地质成藏等基础研究,资源评价、开采技术等应用研究的主要资料来源和强有力支撑。应用于水合物地层的勘探方法主要包括地质、地球物理、地球化学和钻探取心等四类。其中钻探取心是最为直接的勘探手段,可以直接获取原位水合物地层的样品进行分析；地球物理测井在取心困难的情况下就成为最为接近水合物地层原位状态的勘探方法。这两种方法在水合物勘探中占有重要地位,而这两种勘探方式都离不开钻井。通常海洋水合物地层压实固结程度较差,在钻井过程中若采用欠平衡钻井方式,则不利于井壁力学平衡。而且水合物还会因减压而分解,导致地层力学强度急剧降低,更不利于井壁稳定和井内安全。因此,维持孔内压力大于地层孔隙压力、同时不高于破裂压力是水合物钻井较为可取的安全方式。在此条件下,钻井液在水力压差的作用下驱走井壁周围地层孔隙中的原生流体(气、水)而侵入地层。钻井实践证明,钻井液侵入会改变井壁围岩特性,比如岩石强度、孔隙压力等。与钻井液侵入常规油气地层所不同的是,受钻具摩擦生热以及钻井液温度影响,钻井液侵入含水合物地层过程中还可能伴随有水合物的分解,从而加速井壁失稳。此外,在众多的地球物理测井属性中,电阻率和声波速度受水合物的影响最突出。由于海洋区域水合物赋存在固结不好的沉积物中,而声波受压实系数的影响较重,因而电阻率测井又比声波测井和其他测井方法更稳定和可靠。但是,钻井过程中钻井液循环和侵入却对电阻率测井有着显著的影响。比如为抑制水合物在井内形成和保护海洋环境,深水油气和水合物钻井通常采用高盐聚合物水基钻井液体系,当高矿化度钻井液滤液侵入时会严重影响储层特征和电阻率测井准确性。而且盐是热力学抑制剂,其随钻井液侵入会使水合物相平衡曲线向左迁移,导致地层中水合物分解,进一步影响测井识别评价、井周地层稳定和井内安全。因此,研究耦合有水合物分解的水基钻井液侵入含水合物地层的动态特性及其对地层的影响规律对钻井安全预防、测井准确识别和评价、水合物储层保护、水合物资源和环境评估等都具有重要意义和应用价值。针对上述分析,了解钻井液侵入含水合物地层的特性,并采用实验模拟和数值模拟等手段展开研究具有重要意义,据此,论文的主要研究内容和路线包括以下几个方面：(1)分析海洋及冻土区典型水合物储层特征,进行人工岩样的制备研究水合物散布于砂(岩)层孔隙空间是海洋和冻土区最为典型的水合物储层类型之一,同时也最具开采潜力。论文首先对实际的水合物地层岩石物理性质做详细归纳和总结,在此基础上,分析了分散型水合物砂岩储层的主要矿物组成、岩石颗粒尺寸、孔隙分布及连通性、渗流特性等岩石物理特征；使用自主研发的人工岩心制备装置进行人造岩样的制备,并用其模拟真实水合物储层骨架；使用压汞实验仪和渗透率测量仪对所制人工岩样进行孔隙结构分析和渗透性测试,分析人工岩样的物性特征,得到优选的岩心配方和制备工艺；(2)进行钻井液侵入水合物地层的实验模拟研究将制备的人造岩心用于模拟实际的水合物沉积层骨架,使用自主研发、委托厂商生产的“天然气水合物渗流开采综合模拟装置”开展钻井液侵入含水合物地层的相关实验研究,旨在了解钻井液侵入过程中地层物性的变化情况,即掌握钻井液侵入过程中水合物分解程度、地层压力、温度、电学性质的变化等基本规律,并与后续的数值模拟研究相互补充和参考；(3)进行钻井液侵入水合物地层的数值模拟研究在实验模拟受到时间和实验设备功能限制的情况下,通过数值模拟对钻井液侵入水合物地层的相关特性进行了更深入的研究。论文以中国南海神狐海域水合物地层为背景,利用劳伦斯伯克利国家实验室开发的水合物开采数值模拟软件TOUGH+HYDRATE分析了一定条件下钻井液侵入海洋水合物储层的动态过程及其对地层的影响规律,进行了钻井液侵入水合物地层所受的影响因素分析。本论文共六个部分,主要章节内容包括：第一章：本章为论文的绪论部分,首先对天然气水合物做了简单介绍,总结了国内外对天然气水合物的研究历程和现状；对其在全球的分布及储量评估等能源意义,以及自然界中的天然气水合物和人为勘探、开发可能带来的环境问题进行了介绍；并对水合物主要勘探计划和进展情况进行了归纳；介绍了水合物勘探的主要方法,集中分析了水合物地层钻井面临的困难和挑战；引出钻井液侵入水合物地层可能带来的一系列问题,指出了论文研究的目的和意义,并介绍了论文研究的主要内容和技术路线。第二章：本章主要对实际的水合物地层物性进行总结和分析,目的是弄清楚研究对象的基本特征。从微观、中观和宏观三个尺度对原位储层中水合物的分布模式进行了总结和分类；对水合物地层的电学、声学、热学等基本物性,以及孔隙度、水合物饱和度、渗透性、力学性质等储层特性进行了分析和总结,并对通常获取水合物地层物性的实验模拟、实际岩心分析和测井解释三种途径进行了介绍。第三章：目前实验室内模拟水合物沉积物样品时都未全面考虑样品骨架的物性是否贴近实际自然界中的水合物沉积物骨架,从而导致实验结果很难反映或准确代表自然界中的实际情况。为此,本章在第二章对含水合物地层物性进行总结和分析的基础上,对用于模拟实际水合物地层人造岩心的制备技术进行了研究。从目前常规的人造岩心种类中选取适合研究目标的人造岩心技术,确定所模拟地层的基本物性参数后设计正交实验。通过对所制得岩心进行渗透率和孔隙度测量,对比实际水合物地层资料,对实验结果和岩心配方、工艺进行评价和分析,得到了一套较为合理的模拟水合物地层人造岩心制作的配方和工艺,可配制不同孔隙度和渗透率的人造岩心用于相关实验研究。这一工作弥补了水合物地层天然岩心紧缺的不足,对本研究的实验部分顺利进行,及今后水合物室内实验研究提供了便利,具有重要意义。第四章：本章主要是通过实验模拟的手段研究钻井液侵入水合物地层的基本规律和特性。首先对钻井液侵入含水合物地层的过程及原理作了定性分析；然后,介绍了本研究开展过程中自主研制的“水合物地层渗流与开采综合模拟装置”,该装置主要设计初衷就是为研究钻井液侵入含水合物地层特性及其对测井的影响机理,同时也包括了其它功能,比如开采方法研究,综合性较强；利用该设备和第三章优选出的人造岩心进行了水合物形成和分解实验,为钻井液侵入实验的开展奠定了基础；使用盐水模拟实际的海洋钻井液,进行了钻井液侵入水合物地层实验,测试了侵入过程中压力、温度及电阻率变化情况,进一步阐述了钻井液侵入会对原位水合物地层产生扰动。第五章：在实验模拟的基础上,本章通过数值模拟的方法对钻井液侵入水合物地层特性展开了进一步研究。首先介绍了所使用的水合物开采数值模拟软件TOUGH+HYDRATE的基本情况,对理论模型的建立进行了分析；然后,以南海北部神狐海域天然气水合物钻探工程(GMGS-1)为背景,研究了一定条件下钻井液侵入海洋水合物储层的动态过程及其对地层的影响规律,分析了钻井液密度、温度、盐度以及地层绝对渗透率和地层水合物饱和度对钻井液侵入的影响规律。第六章：阐述了本文所得出的主要结论和认识,论文的主要创新点,提出了存在的不足和建议。更多还原

【Abstract】 Natural gas hydrate is a kind of gas hydrate, ice alike crystalline compound composed of water and natural gas molecules with cage structure. Because of its appearance and could ignite with fire, so it is also called "flammable ice","solid gas" or "gas ice". The molecules of natural gas including hydrocarbon (CH4、C2H6、C3H8、C4H10and homologous series) and non-hydrocarbon gases (CO2、N2、H2S etc.), occupied the cavities in water cages. Since methane is the main component of natural gas, the natural gas hydrate with more than99%of methane molecules is commonly referred to as methane hydrate. Gas hydrate is a kind of metastable material, can only be stable under the condition of high pressure and low temperature, mainly exist in bottom sea continental shelf sediments, arctic permafrost, and widely distributed in the slope zone of mainland and islands, uplift of active and passive continental margin, arctic continental shelf and some deep water environment of ocean and inland lake, and even be found in outer space.Since the natural gas hydrates were found in permafrost and seafloor in1960s and1980s respectively, its significance in resource, environment and global warming has evoked the attention of governments, petroleum giants and academic institutions. The study on gas hydrates including flow assurance, drilling operation safety, geological hazard, carbon cycle and climate change, etc., has become a hotspot in earth science and energy research. The level of natural gas research is a reflection of the comprehensive science and technology and potential of sustainable development of a nation to some extent.Studies indicated that the future research of gas hydrate have transformed from the basic research and development plan to applied research such as comprehensive gas hydrate exploitation. The United States has successfully implemented hydrate research program, and owns offshore and Alaska permafrost that have abundant hydrate distribution, is one of the leading countries in gas hydrate research, and have planned to exploit gas hydrate in north slope of Alaska permafrost before2015, and in marine sediments before2025. In addition, Japan, Canada, Germany, Britain, Russia, Norway, South Korea, India, China and other countries have also carried out a large amount of hydrate research. Japan has also planned to commercially exploit gas hydrate before2018. Nigeria, Spain, Chile, Colombia, Peru and New Zealand also showed a strong interest in hydrate research.Preliminary explorations show that the hydrate resource is abundant in China, and the hydrate research has important strategic significance in meeting the energy demand of the country. The gas hydrate research program has been listed in the major project of large scale oil-gas filed and coal bed in the "national medium and long-term (2006-2020) science and technology development plan" in China. In accordance with the macroeconomic policy, the gas hydrate research related scientific activities including investigation, technical system, experimental simulation and environmental and climate issues have increased significantly. Natural gas hydrate has become an important research focus of energy science, and deeply involved in the climate, environment, high technology and global sustainable development.Gas hydrate exploration is the main source of data and support for basic research, such as physical property of hydrate reservoir, geological accumulation and application research including resource evaluation and production technique of gas hydrate. The prospecting methods applied to the hydrate formation are categorized to geologic, geophysical, geochemical and coring drilling. Among them, the coring drilling is the most direct means of exploration, the samples of in-situ hydrates can be directly obtained from hydrate bearing formation for analysis, whereas the geophysical well logging is the method that most close to the in-situ state of hydrate formation when coring is difficult. Therefore, these two methods play an important role in gas hydrates exploration, and neither could be done without drilling.Usually marine hydrate formation is in poor degree of consolidation, if it is drilled by underbalanced drilling methods, is not conducive to borehole stability. Hydrate decomposes under reduced pressure, which also significant reducing the strength of formation, leads to severe borehole wall instability. Therefore, it is preferable to maintain borehole pressure greater than the formation pore pressure while less than fracture pressure during the process of hydrate drilling operation. Under the condition of overbalance, the drilling fluid (i.e. the water based drilling fluid) displaces the original pore fluid (gas and water) around the borehole wall and invades the formation by the pressure differential. The practice of drilling operation indicates that the invasion of drilling fluid would alter the rock properties at the borehole wall, including rock strength, pore pressure etc. Different to invasion of common oil and gas reservoir, the invasion of drilling fluid in gas hydrate formation accompanied by hydrate decomposition caused by drilling tools friction and the temperature of drilling fluid. As a result, the instable of borehole wall accelerated. The resistivity and wave speed are mostly influenced by gas hydrate dissociation amongst all the geophysical logging parameters. The marine hydrate bearing sediments are poorly consolidated, so the acoustic speed is highly affected by compact coefficient, therefore the result of resistivity is more stable and reliable. However, the circulation and invasion of drilling fluid have great influence on resistivity logging. For instance, the high concentration salt and polymer water based drilling fluid systems were applied in order to inhibit the reformation in the borehole and protect the marine environment. The invasion of highly mineralization filtrate would severely alter the characteristics of reservoir and accuracy of resistivity logging. The salt, acting as thermodynamic inhibitor, causes the curve of phase equilibrium moving towards left, results in further gas hydrate dissociation, and has greater effects on evaluation of logging, stability of formation around borehole wall and safety within the borehole. Therefore, the study on the dynamic properties and influence on the formation of invasion of gas hydrate bearing formation by water based drilling fluid coupled by gas hydrate dissociation is meaningful and valuable on safety management, accurate identification and evaluation of geophysical logging, protection of gas hydrate reservoir, assessment of gas hydrate resource and environment, and implementation of well observatory system in IODP.Based on the analysis above, it is important to understand the properties of invasion of gas hydrate formation by drilling fluid, and carry out study by experimental simulation and numerical modeling. The main contents and path of research including:(1) Analysis of the typical characteristic of marine and permafrost gas hydrate bearing formations, and preparation of artificial gas hydrate sample.The research on gas hydrate bearing formation of major ocean and permafrost shows that the gas hydrate distributed in sandstone pore is the most typical hydrate reservoir, and is the most promising energy resources. In the paper, the physical properties of actual gas hydrate bearing formation were firstly summed up. Then the main mineral component, rock particle size, pore distribution and connectivity and seepage characteristics of disseminated type of hydrate formation were analyzed. The artificial core preparation device was independently developed for the preparation of rock sample, in order to simulate the real gas hydrate reservoir.The mercury intrusion instrument and permeability measuring apparatus were applied for the analysis of pore structure and testing of permeability of artificial rock sample. After analyzing the physical property of the artificial stone sample, the optimization of formulation and manufacturing technique of artificial core sample were formed.(2) The simulation research on invasion of gas hydrate bearing formation by drilling fluid.The optimized artificial core samples were selected for simulating the skeleton of gas hydrate bearing sediments. With the application of "comprehensive natural gas hydrate seepage exploitation device" which was self-designed, the research were carried out related to the invasion of simulating gas hydrate bearing formation by drilling fluid, aimed at understanding the change of physical property of formation during the process of drilling fluid invasion. That is obtaining the basic rules of gas hydrate decompose, the evolution of pressure and temperature of formation, and the change of electrical properties during the process as a reference to the result of numerical simulation in the subsequent chapters.(3) Numerical simulation of invasion of gas hydrate bearing formation by drilling fluid.Since the simulation experiment was limited by the function of equipment and time expense, implementing the issues related to invasion of hydrate formation by drilling fluid with numerical simulation method is a good supplement for experimental research, and the efficiency of research would also enhanced. The numerical simulation took the gas hydrate bearing formation in Shenhu area, northern South China sea as background, utilizing numerical simulation exploitation software TOUGH+HYDRATE developed by Lawrence Berkeley national laboratory to analyze the dynamic process of drilling fluid invasion of marine gas hydrate and its influence on the formation at certain conditions, and evaluated the factors that involved during the process.The paper consists of six parts. The main contents are as follows:In the first chapter, firstly the natural gas hydrates were briefly introduced, and the course and state of art of gas hydrate research home and abroad were overviewed. The global distribution, assessment of reserves, as well as gas hydrates in nature, possible environmental problems brought about by human exploration and development were also introduced. The main gas hydrate exploration programs and progresses were summed up. The main methods of gas hydrate exploration were introduced, and the difficulties and problems faced with during drilling operation were analyzed. The problems related to invasion of gas hydrate bearing formations by drilling fluid were introduced and the aim and meaning of the research were also illustrated with the main content and technical route.In the second chapter, the physical properties of actual gas hydrate bearing formation were summed up and analyzed, for the purpose of understanding the basic characteristics of the object of research. The distribution patterns of in situ gas hydrate reservoir were summarized and classified from the macro, meso and micro dimension. The basic physical properties of gas hydrate bearing formations, such as electrical, acoustic, thermal, and porosity, gas hydrate saturation, permeability and mechanical properties were summarized as well. Finally, the three approaches, experimental simulation, actual core analysis and logging interpretation for obtaining the physical properties of actual gas hydrate were compared.In the third chapter, the technique of artificial core sample preparation for simulating actual gas hydrate bearing formation was studied. First chose the appropriate technique of artificial core sample from the conventional methods available. Then the basic physical parameters of the simulating formation were determined before the design of the orthogonal experiment scheme. By comparing the permeability and porosity of the core sample prepared with the actual gas hydrate bearing formation, and evaluating and analyzing the result of experiment, formulation of core and technique, a set of artificial core sample formulation and technique suitable for simulating gas hydrate were obtained. Cores with vary porosity and permeability could be prepared for related experimental tests. This work makes up for the shortage of natural hydrate core sample, therefore it’s important for the ongoing of the simulating experiment and facilitates the future work in the laboratory.In the fourth chapter, the basic rules and behaviors of invasion of gas hydrate bearing formation by drilling fluid were studied by experimental simulation. At first, the process and principle of the invasion were analyzed qualitatively. Then the comprehensive simulating device for seepage and exploitation were introduced. The device was designed for the study of the invasion of gas hydrate formation by drilling fluid, with other functions as well. By utilizing the device and optimized artificial core samples, the experiment of gas hydrate forming and dissociation were conducted, which built the basis for the simulating experiment of gas hydrate invasion. The brine was applied to simulating the marine drilling fluid and the experiment of drilling fluid invasion were carried out. The problems were studied by investigating the evolution of pressure, temperature and resistivity during the process of invasion. The results indicated that the invasion of drilling fluid would disturb the in-situ gas hydrate bearing formation,In the fifth chapter, based on the result of experimental modeling, the problems of drilling fluid were further studied by numerical simulation. Firstly, the numerical simulation exploitation software TOUGH+HYDRATE was introduced and the setup of theoretical model was analyzed. Then the gas hydrate drilling program (GMGS-1) at Shenhu area, northern South China sea were taken as a background, the dynamic process of invasion of marine gas hydrate bearing formation by drilling fluid and its influence on the formation. The factors affecting the invasion of drilling fluid including density, temperature, and salinity of the drilling fluid, absolute permeability and gas hydrate saturation were analyzed as well.In the last chapter, the main conclusions, understandings and innovations were demonstrated, and the shortcomings and suggestions were also proposed.更多还原