【作者】 吴德军；

【导师】 李洋辉；

【作者基本信息】 大连理工大学 ， 动力工程（专业学位）， 2021， 硕士

【摘要】 天然气水合物因其储量丰富、环境友好等特点备受世界各国政府和研究者关注。然而,水合物开采过程会造成储层胶结结构破坏,储层承载力降低,进而可能诱发井筒失稳、海底滑坡以及甲烷气体泄漏等工程地质灾害。阐明水合物储层力学特性是评价开采过程储层稳定性的重要前提。本文主要开展了南海含水合物沉积物剪切和蠕变特性实验研究,阐明了其强度和变形规律,以期为我国南海天然气水合物资源安全开发提供基础数据和理论支撑。首先,测试分析了我国南海神狐海域海洋土基础物性,得到粒径级配、物质组成、微观结构、液塑限及含水率等多项参数,分析发现南海该海域海洋土为级配良好的粘性土,存在石英、伊利石、高岭石、斜长石及绿泥石等多种黏土矿物以及硅藻等结构;海洋土塑性指数为16.86%。其次,开展了海洋土重塑试样常规单级和多级三轴剪切实验,发现无论含水合物还是不含水合物沉积物试样,当有效围压较低时,其应力-应变曲线呈现出显著的应变软化现象,而随着有效围压的增大,逐渐呈现应变硬化趋势;试样强度、弹性模量随着有效围压以及水合物饱和度的增大而增大,而体变随有效围压的增大以及饱和度的减小而增大;多级三轴剪切实验得到的强度、体变规律与常规单级三轴剪切实验较为相似,而弹性模量相差较大,有效围压为0.5 MPa～1 MPa时,多级三轴剪切实验的弹性模量约为常规三轴剪切实验的126%～212%。最后,开展了实验室重塑水合物试样蠕变实验,分析了应力水平、有效围压以及水合物饱和度对南海水合物储层蠕变特性的影响。研究发现:无论是含水合物还是不含水合物沉积物试样,在相同蠕变时间,轴向应变与应变速率均随应力水平、有效围压的增大而增大;试样起始应变与流变起始应变随应力水平、有效围压的增大而增大,而流变起始时间与之相反;相同轴向载荷时,水合物的存在使试样的轴向应变与应变速率显著降低;在含水合物沉积物试样中,含加速蠕变阶段蠕变实验的破坏时间约在80 h,且随有效围压的增大而减小。更多还原

【Abstract】 Natural gas hydrate has attracted the attention of governments and researchers around the world due to its abundant reserves and environmental friendliness.However,the process of hydrate mining will damage the cement structure of the reservoir and reduce the bearing capacity of the reservoir,which may induce engineering geological disasters such as wellbore instability,submarine landslides,and methane gas leakage.Clarifying the mechanical properties of hydrate reservoirs is an important prerequisite for evaluating the stability of the reservoir during the mining process.This paper mainly carried out experimental research on the shear and creep characteristics of hydrate sediments in the South China Sea,clarified its strength and deformation laws,and hoped to provide basic data and theoretical support for the safe development of natural gas hydrate resources in the South China Sea.Firstly,the test analyzed the basic physical properties of the marine soil in the Shenhu area of the South China Sea,and obtained multiple parameters such as particle size gradation,material composition,microstructure,liquid-plastic limit and water content.It is found that the marine soil in this area of the South China Sea is a well-graded cohesive soil;there are a variety of clay minerals such as quartz,illite,kaolinite,plagioclase and chlorite,as well as structures such as diatoms;the plasticity index of marine soil is 16.86%.Secondly,conventional single-stage and multi-stage triaxial shear tests of laboratory reshaped specimens were carried out,and it was found that both hydrate-bearing and hydrate-free sediment specimens,when the effective confining pressure is relatively low,its stress-strain curve shows obvious strain softening,and as the effective confining pressure increases,it gradually shows a strain hardening trend;the strength and elastic modulus of the specimens increase with the increase of the effective confining pressure and hydrate saturation,while the volumetric strain increases with the increase of the effective confining pressure and the decrease of the hydrate saturation;the strength and volumetric strain obtained by the multi-stage triaxial shear test are similar to those of the conventional single-stage triaxial shear test,but the elastic modulus is quite different.When the effective confining pressure is 0.5 MPa ～ 1 MPa,the elastic modulus of the multi-stage triaxial shear experiment is about 126% ～ 212% of the conventional triaxial shear experiment.Finally,a creep test of laboratory remodeled hydrate-bearing specimens was carried out,the effects of stress level,effective confining pressure and hydrate saturation on the creep characteristics of South China Sea hydrate reservoirs are analyzed.The study found that whether it is a hydrate-bearing or hydrate-free sediment specimen,at the same creep time,the axial strain and the strain rate increase with the increase of the stress level and the effective confining pressure;the initial strain of the specimen and the initial rheological strain increase with the increase of the stress level and the effective confining pressure,while the initial rheological time is the opposite;under the same axial load,the presence of hydrate significantly reduces the axial strain and strain rate of the specimen;in the hydrate-bearing sediment specimens,the failure time of the creep experiment with accelerated creep phase is about 80 h,and it decreases with the increase of the effective confining pressure.更多还原