气体水合物沉积物力学特性研究

发布时间：2018-01-06 09:43

本文关键词：气体水合物沉积物力学特性研究　出处：《大连理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：天然气水合物因储量大、清洁无污染等优点,成为世界范围广泛关注、研究的新型能源。中国青藏高原、祁连山冻土带及大兴安岭等地区存在大量冻土区水合物。C02置换法在开采天然气同时可以封存C02,被认为是一种很有前景的开采方式,且在冻土区具有可行性。然而,天然气水合物的开采可能导致储层结构的失稳,进而引起如钻井坍塌、海底滑坡等地质灾害,及温室效应等气候灾害。因此在天然气水合物的商业开采前,必须研究水合物沉积物的强度和变形特性,及水合物开采对矿藏沉积层力学特性的影响。本文针对冻土区CO2置换开采法,开采过程中及开采后沉积物的力学特性进行研究。本研究利用大连理工大学自行研制的TAW-60型低温高压三轴仪,研究了二氧化碳水合物体积分数、围压对CH4、CO2混合水合物沉积物强度和变形特性的影响,建立了水合物沉积物破坏强度σm与二氧化碳水合物体积分数a、围压σ3的变化关系式,及粘聚力c与二氧化碳水合物体积分数α的关系式。结果表明：试样破坏过程可分为弹性变形、应变硬化、试样屈服三阶段；不同围压下,试样最大偏应力都随二氧化碳水合物体积分数的增加呈线性增大；5MPa以下,试样最大偏应力随围压的增加而增大；5MPa以上,试样最大偏应力随围压的增加而减小；试样粘聚力随二氧化碳水合物体积分数的增加近似线性增大,内摩擦角则变化不大且数值较小,粘聚力对试样抗剪强度起主导作用。此外,研究了围压对二氧化碳水合物沉积物蠕变特性的影响,建立了与温度、孔隙度、蠕变加载系数等实验参数关联的流变起始时间及流变速率计算公式。结果表明：试样的蠕变曲线呈现对数形,显示出明显的衰减蠕变特征；试样流变起始时间、流变起始应变和稳态蠕变速率随围压增大呈指数型减小；围压的增大,导致试样抵抗蠕变能力的增强,在低围压条件时尤为明显,高围压下影响趋于微弱。最后,利用岛津公司生产的inspeXio SMX-225CT型微焦点X射线CT系统,首次研究了不同三轴压缩阶段下,甲烷水合物沉积物试样细观结构演变过程。结果表明：试样5%应变以前主要为弹性变形,内部水合物形态、分布变化不大,胶结结构完整,卸荷后高度回弹；5%-15%应变过程主要为塑性变形,试样中部向外隆起,内部存在水合物的变形破碎、颗粒的迁移；15%应变时,试样内部密度小于外部,整体呈剪涨趋势,且内部孔隙发育较差,未出现明显断裂带。
[Abstract]:Because of its large reserves, clean and pollution-free, natural gas hydrate has become a new type of energy, which is widely concerned and studied in the world, and the Qinghai-Tibet Plateau of China. There are a large number of permafrost hydrate. C02 replacement method in the Qilian Mountains and Daxing'an Mountains, which can seal C02 while exploiting natural gas, which is considered to be a promising mining method. However, the exploitation of natural gas hydrate may lead to instability of reservoir structure, which may lead to geological disasters such as drilling collapse, submarine landslide and so on. Therefore, before commercial exploitation of natural gas hydrate, it is necessary to study the strength and deformation characteristics of hydrate sediments. And the effect of hydrate mining on the mechanical properties of deposit deposits. This paper aims at the CO2 displacement mining method in permafrost region. The mechanical properties of sediments during and after mining were studied. The volume fraction of carbon dioxide hydrate was studied by using TAW-60 model low temperature and high pressure triaxial instrument developed by Dalian University of Technology. The effect of confining pressure on the strength and deformation characteristics of CH4CO _ 2 mixed hydrate sediments is studied. The relationship between the destruction strength 蟽 _ m of hydrate sediments and the volume fraction a and 蟽 _ 3 of carbon dioxide hydrate is established. The results show that the failure process can be divided into three stages: elastic deformation, strain hardening and specimen yield. Under different confining pressures, the maximum deflection stress increases linearly with the increase of carbon dioxide hydrate volume fraction. Under 5 MPA, the maximum deflection stress increases with the increase of confining pressure. Above 5 MPA, the maximum deflection stress decreases with the increase of confining pressure. The cohesive force increases linearly with the increase of carbon dioxide hydrate volume fraction, but the internal friction angle changes little and the value is small. The cohesion force plays a leading role in the shear strength of the sample. The influence of confining pressure on creep characteristics of carbon dioxide hydrate sediments was studied. The formula for calculating rheological initiation time and rheological rate associated with experimental parameters such as creep loading coefficient, etc. The results show that the creep curve of the specimen shows logarithmic shape, showing obvious attenuation creep characteristics. The initial rheological strain and steady creep rate decrease exponentially with the increase of confining pressure. The increase of confining pressure leads to the enhancement of the creep resistance of the specimen, especially under low confining pressure, and the influence of high confining pressure tends to be weak. Finally. Using the inspeXio SMX-225CT microfocus X-ray CT system produced by Shimadzu Company, the different triaxial compression stages were studied for the first time. The results show that the strain of sample 5% was mainly elastic deformation, the shape of hydrate in the sample changed little, the cemented structure was intact, and the rebound was high after unloading. The strain process of 5- 15% is mainly plastic deformation, the central part of the specimen is uplifted outwards, the hydrate is deformed and broken, and the particles migrate. When the strain is 15%, the internal density of the specimen is smaller than that of the outside, and the whole specimen is shearing up, and the internal porosity is poor, and there is no obvious fault zone.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE311

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