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1.
利用水饱和法制备含天然气水合物试样,进行等向压缩试验和不排水三轴试验.采用天然气水合物临界状态(M HCS)模型同时预测排水条件和不排水条件下的三轴试验,并进行变动参数分析.不排水条件下,密实纯砂发生应变硬化,而相近密实度的含水合物试样出现应变软化,峰值偏应力随水合物饱和度和围压增大.通过与排水和不排水三轴试验结果的对... 相似文献
2.
为探究相对密度和有效围压对饱和海砂力学特性的影响,利用GDS动态三轴试验仪,对广西北部湾地区海砂开展了一系列固结排水三轴剪切试验,分析了相对密度、有效围压对饱和海砂强度特征、体变特征、割线模量以及摩擦角的影响规律。结果表明：随着围压的减小或相对密度的增大,试样体积应变不断增大,而相对密度或有效围压的增加均会提高试样的峰值强度,有效围压与峰值强度之间呈现良好的线性增长关系。随着围压的减小或相对密度的增大,应力相对软化系数、剪胀系数均不断增大,且有效围压与应力相对软化系数、剪胀系数分别呈线性和半对数线性相关。割线模量随轴向应变的增加整体呈衰减趋势,各试验工况下轴向应变为5%时试样的割线模量相比于轴向应变0.164%衰减了80%~90%。饱和海砂的峰值摩擦角随相对密度的增加而增大,随有效围压的增大而减小,相对密度Dr为50%时有效围压σc为50 kPa对应的峰值摩擦角是σc为200 kPa的1.098倍。 相似文献
3.
利用土工静力-动力液压三轴-扭转多功能剪切仪，针对饱和黏土，在不固结不排水（uu）条件下进行了应力控制式循环扭剪和竖向-扭转耦合试验，通过对试验结果的对比分析探讨了初始预剪应力和应力反向对应力-应变关系特性的影响。并阐述了不同循环应力模式下孔隙水压力发展特性。试验结果表明初始预剪应力对循环应力-应变关系的模式有明显的影响，当初始预剪应力较大且没有应力反向发生时，变形以累积效应为主，当初始剪应力为0时，变形以循环效应为主；不固结不排水条件下的循环孔隙水压力总是在围压附近波动，孔压的波动范围似乎随循环应力的增大而增大，但不具有孔压累积升高的特点。综合考虑剪切变形和正向偏差变形的共同效应，同时为了能够反映平均残余变形和循环变形的影响，建议了一个综合应变破坏标准的算式。进而通过利用试验数据与目前常用的应变标准比较，表明这种破坏标准具有普遍适用性和较好的稳定性，适用于判定各种应力条件下黏土试样破坏及其强度。 相似文献
4.
为研究深海能源土在负压开采过程中含气储层的力学特性,基于含气土赋存理论,提出一种能够控制含气量及气泡大小的制样方法,通过GDS标准应力路径三轴试验系统,开展深海能源土含气储层的固结排水试验研究,分析深海能源土在不同黏土含量及不同含气量下的力学响应规律。研究结果表明：围压变化对深海能源土含气储层的抗剪强度峰值大小影响显著,围压越大抗剪强度峰值越高;黏土含量是决定应力应变曲线变化趋势的关键影响因素,黏土含量越高试样抗剪强度越低,试样抵抗应变软化效应的能力越强;含气土比饱和土体承载能力更低,且承载能力随含气量的增大呈衰减趋势;黏土含量和含气量是深海能源土含气储层抗剪强度指标的重要影响因素,黏土含量、含气量越高,土体自身的总抗剪强度值越低。 相似文献
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6.
为了研究天然气水合物降压开采过程的储层应力及其稳定性，运用线性多孔弹性力学和岩石力学知识，考虑水合物储层原始应力、孔隙压力、渗流附加应力及降压开采水合物过程中水合物饱和度的变化，建立了降压开采天然气水合物储层的力学模型，结合墨西哥湾某处水合物藏的基本参数，对降压开采水合物储层应力变化和开采过程的储层稳定性进行研究。结果表明：井底压力是影响水合物储层应力变化的关键因素之一；渗流附加应力在一定程度上减小了储层的应力；水合物分解储层应力发生变化，储层应力在井壁处的波动最大，井壁处是整个储层所受轴向偏应力最大的位置，因此井壁处是优先发生剪切破坏的位置；为了储层的稳定性，降压开采水合物生产压差应小于2.19 MPa。 相似文献
7.
《中国海洋大学学报(自然科学版)》2017,(10)
以中国近海某天然气水合物(水合物)区的海底粉质黏土制备水合物沉积物样品,并在土工三轴仪上进行实验,分析其应力应变曲线和破坏应力特性。结果表明:力学常数如破坏应力(应变为15%对应的偏应力)随水合物饱和度的增加而增加,在饱和度约25%时破坏应力产生跳跃,即破坏应力随水合物饱和度的变化可分为两部分,饱和度小于25%时水合物的存在对沉积物破坏应力影响较小,大于25%时影响较大。在水合物饱和度小于45%的范围内,水合物沉积物的应力应变曲线可分为弹性段、屈服段和强化段。文中给出了描述其应力应变曲线的分段函数。 相似文献
8.
低围压水平下砂的排水行为(英文) 总被引：2，自引：1，他引：2
采用干样沉降法制备样品 ,选用静三轴仪对松砂和密砂样在 10 k Pa至 10 0 k Pa的低围压下的排水行为进行了实验研究 ,并对实验结果作了橡皮膜校正 ,在围压为 10 k Pa的密砂实验中 ,轴向应力的校正值可达到 12 %。实验研究表明低围压下松砂的剪胀性非常明显 ,且存在剪应力极值 ;围压越低 ,松砂和密砂的剪应力极值越小 ,达到最大剪应力所对应的剪应变越小。同时还表明低围压范围内相对密度不同 ,砂的应力应变特性不同 ;此外 ,低围压下砂的内摩擦角高于高围压下的值 ,从而在工程上应重视低围压水平下砂土工程参数的合理选取 相似文献
9.
循环应力下饱和黏土剪切变形特性试验研究 总被引：3，自引：0，他引：3
针对饱和重塑黏土,利用土工静力-动力液压三轴-扭转多功能剪切仪,在不固结不排水(UU)条件下进行了应力控制式循环扭剪和竖向-扭转耦合试验,通过对试验结果的对比分析探讨了初始预剪应力和应力反向对应力-应变关系特性的影响,并阐述了不同加荷模式下孔隙水压力发展特性。以此为基础,综合考虑剪切变形和正向偏差变形的共同效应,同时为了能够反映平均残余变形和循环变形的影响,建议了一个综合应变破坏标准的算式。进而通过利用试验数据与目前常用的应变标准比较,表明这种破坏标准具有普遍适用性和较好的稳定性,适用于判定各种应力条件下黏土试样破坏及其强度。 相似文献
10.
水合物开采可能诱发海底滑坡或其他工程地质灾害。实现水合物商业化开采需要中长期稳定产气，长期荷载下储层的蠕变特性是地层稳定性评价的基础力学参数。利用南海水合物储层粉黏土为试验介质在压缩加载条件下的系列固结排水蠕变测量试验结果，对粉黏土的蠕变特性进行了分析。结果表明，加载过程中，含水合物沉积物经历瞬时变形、固结变形和蠕变变形3个阶段；随着加载应力和水合物饱和度的提高，蠕变应变不断增加；修正的Singh-Mitchell蠕变模型可以较好预测不同应力水平和水合物饱和度下粉黏土的蠕变特性。 相似文献
11.
Megan Elwood Madden Shannon Ulrich Phillip Szymcek Scott McCallum Tommy Phelps 《Marine and Petroleum Geology》2009
In order for methane to be economically produced from the seafloor, prediction and detection of massive hydrate deposits will be necessary. In many cases, hydrate samples recovered from seafloor sediments appear as veins or nodules, suggesting that there are strong geologic controls on where hydrate is likely to accumulate. Experiments have been conducted examining massive hydrate accumulation from methane gas bubbles within natural and synthetic sediments in a large volume pressure vessel through temperature and pressure data, as well as visual observations. Observations of hydrate growth suggest that accumulation of gas bubbles within void spaces and at sediment interfaces likely results in the formation of massive hydrate deposits. Methane hydrate was first observed as a thin film forming at the gas/water interface of methane bubbles trapped within sediment void spaces. As bubbles accumulated, massive hydrate growth occurred. These experiments suggest that in systems containing free methane gas, bubble pathways and accumulation points likely control the location and habit of massive hydrate deposits. 相似文献
12.
沉积物孔隙毛细管压力与甲烷水合物饱和度关系研究 总被引：1，自引：1，他引：0
To better understand the relationship between the pore capillary pressure and hydrate saturation in sediments, a new method was proposed. First, the phase equilibria of methane hydrate in fine-grained silica sands were measured. As to the equilibrium data, the pore capillary pressure and saturation of methane hydrate were calculated. The results showed that the phase equilibria of methane hydrates in fine-grained silica sands changed due to the depressed activity of pore water caused by the surface group and negatively charged characteristic of silica particles as well as the capillary pressure in small pores together. The capillary pressure increased with the increase of methane hydrate saturation due to the decrease of the available pore space. However, the capillary-saturation relationship could not yet be described quantitatively because of the stochastic habit of hydrate growth. 相似文献
13.
This paper describes studies of the effect of hydrate dissociation on the safety and stability of methane hydrate-bearing sediments. Methane hydrates within the sediments were dissociating under the conditions of a confining pressure of 0.5 MPa, 1 MPa, 2 MPa and a temperature of −5 °C. After 6 h, 24 h, or 48 h, a series of triaxial compression tests on methane hydrate-bearing sediments were performed. The tests of ice-clay and sediments without hydrate dissociation were performed for comparison. Focusing on the mechanical properties of the sediments, the experimental results indicated that the shear strength of the ice-clay mixtures was lower than that of the methane hydrate-bearing sediments. The strength of the sediments was reduced by hydrate dissociation, and the strength tended to decrease further at the lower confining pressures. The secant modulus ES of the sediments dropped by 42.6% in the case of the dissociation time of the hydrate of 48 h at the confining pressure of 1 MPa; however, the decline of the initial yield modulus E0 was only 9.34%. The slower hydrate dissociation rate contributed to reducing the failure strength at a declining pace. Based on the Mohr–Coulomb strength theory, it was concluded that the decrease in strength was mainly affected by the cohesive reduction. Moreover, the mathematical expression of the M–C criterion related to the hydrate dissociation time was proposed. This research could be valuable for the safety and stability of hydrate deposits in a permafrost region. 相似文献
14.
The present paper focuses on heat and mass exchange processes in methane hydrate fragments during in situ displacement from the gas hydrate stability zone (GHSZ) to the water surface of Lake Baikal. After being extracted from the methane hydrate deposit at the lakebed, hydrate fragments were placed into a container with transparent walls and a bottom grid. There were no changes in the hydrate fragments during ascent within the GHSZ. The water temperature in the container remained the same as that of the ambient water (~3.5 °С). However, as soon as the container crossed the upper border of the GHSZ, first signs of hydrate decomposition and transformation into free methane gas were observed. The gas filled the container and displaced water from it. At 300 m depth, the upper and lower thermometers in the container simultaneously recorded noticeable decreases of temperature. The temperature in the upper part of the container decreased to –0.25 °С at about 200 m depth, after which the temperature remained constant until the water surface was reached. The temperature at the bottom of the container reached –0.25 °С at about 100 m depth, after which it did not vary during further ascent. These observed effects could be explained by the formation of a gas phase in the container and an ice layer on the hydrate surface caused by heat consumption during hydrate decomposition (self-preservation effect). However, steady-state simulations suggest that the forming ice layer is too thin to sustain the hydrate internal pressure required to protect the hydrate from decomposition. Thus, the mechanism of self-preservation remains unclear. 相似文献
15.
Tian-Shun Hou Wei Wang Ya-Sheng Luo Jin-Qian Dang Xiu-Juan Yang 《Marine Georesources & Geotechnology》2013,31(3):264-276
To reveal the influence of material composition on mechanical properties of light-weight soil, stress-strain -volumetric strain characteristics and Poisson's ratio of mixed soil were researched by consolidated drained shear tests. The results show that light-weight soil is a kind of structural soil, so its mechanical properties are affected by mixed ratio and confining pressure, and mixed soil possesses structural yield stress. When confining pressure is less than the structural yield stress, strain softening occurs; when confining pressure is more than the structural yield stress, strain hardening is observed. There are two kinds of volume change behavior: shear contraction and shear dilatancy. Shear dilatancy usually leads to strain softening, but there isn't an assured causal relationship between them. Poisson's ratio of mixed soil is a variational state parameter with the change of stress state, it decreases with increased confining pressure, and it increases with increased stress level. When axial strain is near 5%, Poisson’ ratio is gradually close to a steady value. The main range of Poisson's ratio is 0.25～0.50 when confining pressure changes from 50 to 300 kPa. When unconfined compressive strength of mixed soil is less than 328 kPa, its stress-strain-volumetric strain characteristics can be predicted very well by Duncan-Chang model (E-B model). However, when the range of unconfined compressive strength is [328 kPa, 566 kPa], the model can't predict stress-strain characteristics accurately when confining pressure is under 200 kPa, and it also can't predict the strong shear dilatancy phenomenon of mixed soil under low confining pressure. 相似文献
16.
用吹扫-捕集法对东沙群岛西南和西沙海槽附近海域5个站位水柱中的甲烷浓度进行了测定,在其中的3个站位发现了甲烷高浓度异常。在东沙群岛西南海域的E105A和E106两站位近底层海水中甲烷浓度均出现异常增加,其值分别为4.25和10.64 nmol/dm3。在西沙海槽附近的E413站位甲烷异常出现在1 750,1 900和2 050 m深的近底层水中,浓度分别达5.17,8.48和8.70 nmol/dm3。在近底层海水中出现的甲烷高浓度异常是由于沉积物下部甲烷渗漏活动造成的,结合前人在这两个海域沉积物的地球物理和化学调查资料,认为可能是与冷泉渗漏或天然气水合物分解有关。2007年5月在探测到甲烷高浓度明显异常的东沙群岛西南神弧海域,获得了天然气水合物的实物样品,但是西沙海槽附近海域近底层水的甲烷高浓度异常是来源于天然气水合物还是来源于冷泉需要进一步加以确认。 相似文献
17.
AbstractIn this article, the dilatancy of calcareous soil is studied systematically based on triaxial consolidation drainage shear tests, and the difference in dilatancy between calcareous soil and siliceous soil is also investigated. It was found that: ① Calcareous soil experience obvious dilated deformation. Dilatancy tendency increases with increasing related density and decreases with increasing confining pressure. ② The volumetric strain rate initially increases from negative to positive. After it reaches a maximum, there is a small decrease in the volumetric strain rate, but it is still greater than zero, and the stress-strain curves are of softening type. ③ For the same condition, the dilatancy deformation of calcareous sand begins later than that of siliceous sand, and the volume compression before dilatancy is also larger for calcareous sand. ④ The critical state alone cannot accurately describe the entire deformation process of soil, and it is proposed that the phase transformation state be added to the standard method used to assess soil dilatation and contraction. ⑤ Based on the statistical analysis of experimental data, mathematical relationships were established between void ratio, relative density, and effective confining pressure of phase transformation state and critical state, respectively.
- Highlights
Reports results from a well-designed experiment that includes a good amount of samples and data.
Effects of relative density and effective confining pressure on deformation mode and mechanical properties of calcareous sand are evaluated.
The difference in dilatancy between calcareous sand and siliceous sand was compared
The phase-transformation state and critical state were compared with the axial strain, volumetric strain and deviatoric stress.
Using phase-transformation void ratio and critical void ratio to describe the whole deformation process of calcareous sand is proposed.
The mathematical expressions of phase-transformation void ratio and critical void ration were given, respectively.
18.
印度国家天然气水合物计划(NGHP01)于2016年实施第1次钻探,证实了天然气水合物在印度大陆边缘的广泛分布。选择位于克里希纳-戈达瓦里盆地(KG盆地)的NGHP01-07D和NGHP01-15A钻孔,基于测井数据和岩心样品估算天然气水合物饱和度,分析天然气水合物赋存状态并探讨其形成机制。基于各向同性介质模型利用电阻率和声波测井计算NGHP01-15A钻孔的天然气水合物饱和度为0. 2%～33. 0%,平均值为9. 6%,在NGHP01-07D钻孔利用电阻率计算获得的天然气水合物饱和度高于岩心氯离子异常和气体释放获得的结果,但是基于各向同性岩石物理模型利用声波测井计算的天然气水合物饱和度与岩心结果一致,平均值为5. 0%。前人研究认为NGHP01-10D钻孔中天然气水合物以相对较高饱和度富集在高角度裂隙中。结合前人研究结果推断在克里希纳-戈达瓦里盆地存在3种不同的天然气水合物储层,即泥岩中砂质夹层各向同性储层、泥质/粉砂质高角度低连通性的低饱和度裂隙储层和泥岩中高角度高连通性的高饱和度裂隙储层,并提出对应的3种天然气水合物储层模型。 相似文献