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1.
Erling Fjær 《Geophysical Prospecting》2019,67(1):128-139
Static moduli of rocks are usually different from the corresponding dynamic moduli. The ratio between them is generally complex and depends on several conditions, including stress state and stress history. Different drainage conditions, dispersion (often associated with pore fluid effects), heterogeneities and strain amplitude, are all potential reasons for this discrepancy. Moreover, comparison of static and dynamic moduli is often hampered and maybe mistaken due to insufficient characterization of anisotropy. This paper gives a review of the various mechanisms causing differences between static and dynamic moduli. By careful arrangements of test conditions, it is possible to isolate the mechanisms so that they can be studied separately. Non-elastic deformation induced by the large static strain amplitudes is particularly challenging, however a linear relationship between non-elastic compliance and stress makes it possible to eliminate also this effect by extrapolation to zero strain amplitude. To a large extent, each mechanism can be expressed mathematically with reasonable precision, thus quantitative relations between the moduli can be established. This provides useful tools for analyses and prediction of rock behaviour. For instance, such relations may be used to predict static stiffness and even strength based on dynamic measurements. This is particularly useful in field situations where only dynamic data are available. Further, by utilizing the possibility for extrapolation of static measurements to zero strain amplitude, dispersion in the range from seismic to ultrasonic frequencies may be studied by a combination of static and dynamic measurements. 相似文献
2.
Alexey Yurikov Maxim Lebedev Marina Pervukhina Boris Gurevich 《Geophysical Prospecting》2019,67(4):984-996
Shales play an important role in many engineering applications such as nuclear waste, CO2 storage and oil or gas production. Shales are often utilized as an impermeable seal or an unconventional reservoir. For both situations, shales are often studied using seismic waves. Elastic properties of shales strongly depend on their hydration, which can lead to substantial structural changes. Thus, in order to explore shaly formations with seismic methods, it is necessary to understand the dependency of shale elastic properties on variations in hydration. In this work, we investigate structural changes in Opalinus shale at different hydration states using laboratory measurements and X-ray micro-computed tomography. We show that the shale swells with hydration and shrinks with drying with no visible damage. The pore space of the shale deforms, exhibiting a reduction in the total porosity with drying and an increase in the total porosity with hydration. We study the elastic properties of the shale at different hydration states using ultrasonic velocities measurements. The elastic moduli of the shale show substantial changes with variations in hydration, which cannot be explained with a single driving mechanism. We suggest that changes of the elastic moduli with variations in hydration are driven by multiple competing factors: (1) variations in total porosity, (2) substitution of pore-filling fluid, (3) change in stiffness of contacts between clay particles and (4) chemical hardening/softening of clay particles. We qualitatively and quantitatively analyse and discuss the influence of each of these factors on the elastic moduli. We conclude that depending on the microstructure and composition of a particular shale, some of the factors dominate over the others, resulting in different dependencies of the elastic moduli on hydration. 相似文献
3.
Samuel Chapman Jan V. M. Borgomano Hanjun Yin Jerome Fortin Beatriz Quintal 《Geophysical Prospecting》2019,67(4):956-968
Fluid pressure diffusion occurring on the microscopic scale is believed to be a significant source of intrinsic attenuation of mechanical waves propagating through fully saturated porous rocks. The so-called squirt flow arises from compressibility heterogeneities in the microstructure of the rocks. To study squirt flow experimentally at seismic frequencies the forced oscillation method is the most adequate, but such studies are still scarce. Here we present the results of forced hydrostatic and axial oscillation experiments on dry and glycerine-saturated Berea sandstone, from which we determine the dynamic stiffness moduli and attenuation at micro-seismic and seismic frequencies (0.004–30 Hz). We observe frequency-dependent attenuation and the associated moduli dispersion in response to the drained–undrained transition (∼0.1 Hz) and squirt flow (>3 Hz), which are in fairly good agreement with the results of the corresponding analytical solutions. The comparison with very similar experiments performed also on Berea sandstone in addition shows that squirt flow can potentially be a source of wave attenuation across a wide range of frequencies because of its sensitivity to small variations in the rock microstructure, especially in the aspect ratio of micro-cracks or grain contacts. 相似文献
4.
Liquefaction of seabed under seismic loading is one of the main points that govern the overall stability of submarine pipeline. However, most previous investigations concerned only with free seabed and searched for seismic accumulative excess pore pressure by solving Terzaghi's consolidation equation containing pore pressure source term. It is not able to introduce two-dimensional structures such as submarine pipelines in one-dimensional problem, and it is also not able to obtain the distribution of seismic accumulative excess pore pressure in seabed around submarine pipelines by such a way. In this study, a FEM numerical analysis method for determining the liquefaction of sandy seabed around a buried pipeline under seismic loading is presented. The empirical mode of dynamic increase of pore pressure under undrained shearing induced by seismic loading is incorporated with two-dimensional dynamic consolidation equation and a numerical procedure based on FEM is developed to assess the accumulative excess pore pressure. By numerical computations, the accumulative process of pore pressure and liquefaction potential of seabed soil during seismic loading is evaluated. From a series of numerical computations based on the presented model with various parameters, the effects of soil characteristic parameters and pipeline geometry on seismic accumulative excess pore pressure around submarine pipeline and along the depth of seabed are explored in detail. 相似文献
5.
In Switzerland the geological storage in the Opalinus Clay formation is the preferred option for the disposal of spent fuel (SF) and high-level radioactive waste (HLW). The waste will be encapsulated in steel canisters and emplaced into long tunnels that are backfilled with bentonite. Due to uncertainties in the depth of the repository and the associated stress state, a concrete liner might be used for support of emplacement tunnels.Numerical reactive transport calculations are presented that investigate the influence of a concrete liner on the adjacent barrier materials, namely bentonite and Opalinus Clay. The geochemical setup was tailored to the specific materials foreseen in the Swiss repository concept, namely MX-80 bentonite, low-pH concrete (ESDRED) and Opalinus Clay. The heart of the bentonite model is a new conceptual approach for representing thermodynamic properties of montmorillonite which is formulated as a multi-component solid solution comprised of several end-members.The presented calculations provide information on the extent of pH fronts, on the sequence and extent of mineral phase transformations, and on porosity changes on cement–clay interfaces. It was found that the thickness of the zone containing significant mineralogical alterations is at most a few tens of centimeters thick in both the bentonite and the Opalinus Clay adjacent to the liner. Near both interfaces, bentonite–concrete liner and concrete liner–Opalinus Clay, the precipitation of minerals causes a reduction in the porosity. The effect is more pronounced and faster at the concrete liner–Opalinus Clay interface. The simulations reveal that significant pH-changes (i.e. pH > 9) in bentonite and Opalinus Clay are limited to small zones, less than 10 cm thick at the end of the simulations. It is not to be expected that the zone of elevated pH will extend much further at longer times. 相似文献
6.
B. J. RAFISON 《Geophysical Prospecting》1988,36(8):847-856
Determination of petrography and pore fluid content is an ultimate goal of an integrated seismic-petrophysical study. For lack of a general inversion technique, forward modelling is useful in studying the relations between lithology, stratigraphy, pore fluid content and the seismic response. This report describes a study of two clastic sequences in Utah, from which 32 rock samples were analysed. A detailed petrographic study was done. Laboratory measurements were made of ultrasonic compressional- and shear-wave velocity as a function of pressure. We computed the velocities at seismic frequencies for the samples when dry, over-pressured, brine saturated, and oil saturated. The velocities were sensitive to the porosity, carbonate cementation and the depositional facies. We generated velocity profiles for hypothetical reservoirs for a range of saturation states. The velocity profiles were used to generate synthetic seismic shot gathers to study the seismic response of these clastic reservoirs. The fluid-saturation strongly affects the seismic respone, as does the presence of a coal seam. An amplitude change with offset is often observed. However, stratigraphy appears to have a stronger effect on the seismic response. 相似文献
7.
Flow failure of sandy subsoil induced by seismic liquefaction is known to cause significant damage to structures. It is induced not only by the dynamic forces exerted by seismic acceleration but also by the static gravity force in consequence of the topography of the ground. The ground flow may sometimes continue after the end of the seismic loading and finally the ground is significantly deformed to cause a failure.This paper numerically predicts the magnitude of flow that could occur when soil liquefaction continues for a sufficiently long period. It is considered that liquefied soil behaves like a viscous liquid, and hence, ground flow is governed by the principle of minimum potential energy. In the calculation, liquefied sand is assumed to be a viscous liquid that deforms in undrained conditions with its volume remaining constant. To consider the non-linearity due to large displacement, the updated Lagrangian method is used to solve the equation of motion. The Newmark β method is employed to calculate the time history of the ground motion. Finally, a simulation using this calculation method shows that the proposed method gives reasonable results for the conditions indicated. 相似文献
8.
Experimental measurements of fracture-induced seismic waves velocity variations at frequencies ~ 1 kHz, ~ 40 kHz and ~ 1 MHz were performed directly in the field at the rocky outcrop and in the laboratory on specific rock samples collected from the outcrops. The peridotite–lherzolite outcrop appeared macroscopically uniform and contained three systems of visible parallel sub-vertical fractures. This rock has substantial bulk density and higher than average value of seismic wave velocity. The presence of fracture systems gives rise to its velocity anisotropy. The seismic waves passing through the rock fractures are subject to velocity dispersion and frequency dependent attenuation. Our data, obtained from field and laboratory measurements, were compared with theoretical model predictions. In this model we successfully used displacement discontinuity approach. For the velocity dispersion evaluation we used multi-frequency measurements. The a priori observation of orientations and densities of fracture sets allowed evaluation of their stiffness. Our approach revealed that the first arrivals of seismic waves can be used for evaluation of P-wave group velocities, the specific case, in which we expect anomalous velocity dispersion. Our observations contribute to the issue of up-scaling of well-log derived velocities in fractured rock to the scale of standard seismic exploration frequencies. 相似文献
9.
Influence of subsurface injection on time‐lapse seismic: laboratory studies at seismic and ultrasonic frequencies 
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下载免费PDF全文 Seismic monitoring of reservoir and overburden performance during subsurface CO2 storage plays a key role in ensuring efficiency and safety. Proper interpretation of monitoring data requires knowledge about the rock physical phenomena occurring in the subsurface formations. This work focuses on rock stiffness and elastic velocity changes of a shale overburden formation caused by both reservoir inflation induced stress changes and leakage of CO2 into the overburden. In laboratory experiments, Pierre shale I core plugs were loaded along the stress path representative for the in situ stress changes experienced by caprock during reservoir inflation. Tests were carried out in a triaxial compaction cell combining three measurement techniques and permitting for determination of (i) ultrasonic velocities, (ii) quasistatic rock deformations, and (iii) dynamic elastic stiffness at seismic frequencies within a single test, which allowed to quantify effects of seismic dispersion. In addition, fluid substitution effects connected with possible CO2 leakage into the caprock formation were modelled by the modified anisotropic Gassmann model. Results of this work indicate that (i) stress sensitivity of Pierre shale I is frequency dependent; (ii) reservoir inflation leads to the increase of the overburden Young's modulus and Poisson's ratio; (iii) in situ stress changes mostly affect the P‐wave velocities; (iv) small leakage of the CO2 into the overburden may lead to the velocity changes, which are comparable with one associated with geomechanical influence; (v) non‐elastic effects increase stress sensitivity of an acoustic waves; (iv) and both geomechanical and fluid substitution effects would create significant time shifts, which should be detectable by time‐lapse seismic. 相似文献
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孔隙尺度的喷射流流动是引起地震波速度频散和衰减的重要机制之一.目前,大多数喷射流模型仅考虑硬孔隙与微裂隙之间的局部流动,而忽略了具有不同孔隙纵横比微裂隙间的喷射流作用.为了研究各种类型孔隙间的流体流动效应,本文对经典喷射流模型进行了扩展,通过结合等效介质理论和孔隙结构模型,根据从干燥岩石超声速度-压力曲线中提取的微裂隙孔隙纵横比分布,求取出岩石中各种微裂隙的体积压缩系数,并在此基础上,利用孔隙空间的压力松弛效应对微裂隙间的喷射流效应进行了模拟,并运用Biot理论描述了硬孔隙间的宏观流动效应.扩展后的理论模型不仅考虑了微裂隙与硬孔隙间的局部流动、硬孔隙与硬孔隙间的Biot宏观流,还加入了微裂隙与微裂隙间的喷射流作用,且模型的高、低频极限始终与Mavko-Jizba理论和Gassmann方程保持一致.模型应用分析发现,对于砂岩和大部分致密灰岩样品,扩展模型均能给出与超声实验测量数据吻合良好的估计结果.此外,扩展模型预测的速度频散及衰减表明,喷射流机制在地震和测井频段发挥着重要作用,其速度频散曲线由低频至高频呈逐渐增大趋势,不具有明显的快速变化特征,与经典频散曲线形态存在显著差异;在低有效压力下,频散和衰减程度较大,喷射流机制发挥主要作用,而随着有效压力的增加,Biot宏观流机制开始占主导,频散和衰减程度逐渐减小. 相似文献
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为了研究孔隙流体对不同渗透率岩石地震波速度的影响,在实验室利用跨频带岩石弹性参数测试系统得到了应变幅值10-6的2~2000Hz频段下的地震波速度和1 MHz频率下的超声波速度,利用差分共振声谱法得到了频率600Hz岩石干燥和完全饱水情况下岩石声学参数.实验表明,在低饱和度下,致密砂岩在地震和超声频段下没有明显的频散;在高饱和度下纵波速度的频散变得明显.从干燥到完全水饱和条件,不同频率测量的致密砂岩的体积模量随岩石孔隙度增高而降低,且体积模量的变化量受岩石微观孔隙结构的影响较大.高孔、高渗砂岩无论在低含水度下还是在高含水饱和度下频散微弱,并且在地震频段下围压对于岩石纵横波速度的影响要大于频率的影响.高孔、高渗砂岩和致密砂岩不同含水饱和度下的频散差异可应用于储层预测,油气检测等方面,同时该研究可以更好地帮助理解岩石的黏弹性行为,促进岩石物理频散理论的发展,提高地震解释的精度. 相似文献
14.
Shunichi Sawada Yoshimichi Tsukamoto Kenji Ishihara 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):175-182
Multiple series of triaxial tests were carried out on unsaturated sandy soils subjected to irregular seismic excitation. To observe the volume changes of unsaturated soil specimens during undrained loading and subsequent process of drainage, the inner cell was newly installed inside the large triaxial cell. The soil samples tested were recovered from the construction site of a liquefied natural gas storage facility located in Tokyo Bay area. In the tests, the initial conditions of soil specimens were specified with the degrees of saturation Sr of 50, 75 and 100%. The soil specimens were anisotropically consolidated, and subjected to undrained irregular seismic excitation. The time history of irregular seismic excitation was the one obtained from one of the recent earthquakes in Japan. The drainage line was then opened to let the excess pore water drain out of soil specimens. The volume changes and residual shear strains of unsaturated soil specimens thus obtained are presented in the present paper. 相似文献
15.
《Physics and Chemistry of the Earth》2004,29(1):3-15
This paper addresses the achievements in understanding the hydrogeological conditions in the low permeability claystone formation of the Opalinus Clay at the Mont Terri Rock Laboratory. The synthesis work consisted of (i) an assessment of clay-specific artifacts which may affect the interpretation of hydraulic tests, (ii) a survey of hydraulic rock properties such as hydraulic conductivity and storage coefficient, and (iii) an assessment of the governing flow laws and definition of hydrogeological units and flow boundaries on the site scale. Drawing on the broad hydrogeological data base, confidence is gained in the hydraulic barrier function of the Opalinus Clay, which effectively prevents groundwater flow between the over- and underlying aquifer systems. 相似文献
16.
Hui Li Luanxiao Zhao De-hua Han Jinghuai Gao Hemin Yuan Yirong Wang 《Geophysical Prospecting》2020,68(9):2808-2824
Investigating seismic dispersion and attenuation characteristics of loosely compacted marine sandstone is essential in reconciling different geophysical measurements (surface seismic, well logging and ultrasonic) for better characterization of a shallow marine sandstone reservoir. We have experimented with a typical high-porosity and high-permeability sandstone sample, extracted from the Paleogene marine depositional setting in the Gulf of Mexico, at the low-frequency band (2–500 Hz) as well as ultrasonic point (106 Hz), to investigate the effects of varying saturation levels on a rock's elasticity. The results suggest that the Young's modulus of the measured sample with adsorbed moisture at laboratory conditions (room temperature, 60%–90% humidity) exhibits dispersive behaviours. The extensional attenuation can be as high as 0.038, and the peak frequency occurs around 60 Hz. The extensional attenuation due to moisture adsorption can be dramatically mitigated with the increase of confining pressure. For partial saturation status, extensional attenuation increases as increasing water saturation by 79% with respect to the measured frequencies. Additionally, the results show that extensional attenuation at the fully water-saturated situation is even smaller than that at adsorbed moisture conditions. The Gassmann–Wood model can overall capture the P-wave velocity-saturation trend of measured data at seismic frequencies, demonstrating that the partially saturated unconsolidated sandstone at the measured seismic frequency range is prone to be in the relaxed status. Nevertheless, the ultrasonic velocities are significantly higher than the Gassmann–Wood predictions, suggesting that the rocks are in the unrelaxed status at the ultrasonic frequency range. The poroelastic modelling results based on the patchy saturation model also indicate that the characteristic frequency of the partially saturated sample is likely beyond the measured seismic frequency range. 相似文献
17.
A new smooth hysteretic model for ductile flexural‐dominated reinforced concrete bridge columns 下载免费PDF全文
下载免费PDF全文 A new smooth hysteretic model is proposed for ductile, flexural‐dominated reinforced concrete bridge columns. Four columns designed per modern seismic codes were tested using monotonically increasing and variable‐amplitude cyclic loading protocols and ground motion loading to develop the model. Based on the test results, hysteretic rules for damage accumulation and path dependence of reloading were constructed. For damage accumulation, unloading stiffness degradation is correlated with the maximum displacement and hysteretic energy dissipation, while reloading stiffness degradation is set equal to the unloading stiffness degradation. Pinching severity is related to the residual displacement in the direction opposite to the loading direction. Strength deterioration is correlated with the damage index and does not occur until the damage index reaches a threshold, after which the deterioration is proportional to the increase of the damage index. For path dependence of reloading, reloading paths are classified into primary paths and associate paths. The primary paths are those that start from a residual displacement that is equal to or larger than the previous maximum one. The associate paths are those that do not belong to primary paths and tend to be directed towards certain points. Reloading without load reversal is assumed to be linear. Comparison with the results of pseudo‐dynamic tests using three consecutive ground motions showed that the proposed model closely matched the test results. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
18.
复杂应力条件下松砂振动孔隙水压力与体变特性的试验研究 总被引：5，自引：2，他引：3
利用新研制的土工静力-动力液压三轴-扭转多功能剪切仪,在5种初始主应力方向角与5种中主应力系数相组合的初始固结条件下,对饱和松砂进行了不排水循环扭剪试验。讨论了初始固结条件对不排水条件下饱和松砂孔隙水压力变化规律及对剪胀、剪缩、卸荷体缩等体积变化过程的影响。试验研究表明：（1）分别以稳定残余孔隙水压力和破坏时循环次数归一化后的残余孔隙水压力比和循环次数比之间的关系可以用双曲线模式表达。其参数主要依赖于初始主应力方向,中主应力系数对参数的影响并不显著。归一化后的孔隙水压力比与广义剪应变之间的关系也可以用双曲线模式表达,其中的2个待定参数依赖于初始主应力方向,与中主应力系数无关;（2）在三向非均等固结条件下的不排水循环扭剪试验中,饱和松砂表现出卸荷体缩特性,不同初始主应力方向时,饱和松砂剪缩、剪胀、卸荷体缩呈现出不同的交替变化模式。 相似文献
19.
为了研究自复位中心支撑钢框架（SC-CBF）结构的抗震性能,对一四层SC-CBF结构进行了静力弹塑性分析、低周往复加载分析和动力弹塑性时程分析,并与中心支撑钢框架（CBF）结构进行对比,探究了不同GAP单元刚度和预应力筋截面积对SC-CBF结构自复位性能及抗震性能的影响规律。结果表明:与传统CBF结构相比,SC-CBF结构的抗侧能力强,地震作用下基底剪力小,卸载后的残余变形较小,具有良好的延性性能;在极罕遇地震作用下SC-CBF结构的位移响应大,耗散的能量多,层间位移角大而残余位移小,表现出良好的自复位性能和抗震性能;GAP单元刚度对预应力筋的受力性能影响较为明显,对结构的整体受力性能和延性性能影响较小,但结构的整体受力性能和延性性能受预应力筋截面积影响显著。 相似文献
20.
V. Sarhosis P. Asteris T. Wang W. Hu Y. Han 《Bulletin of Earthquake Engineering》2016,14(4):1131-1152
The structural behavior of colonnade structural systems subjected to static and dynamic loading is investigated to identify the main factors affecting the stability and to improve our understanding of their behaviour. In particular, the discrete element method of analysis is utilised to study the static and dynamic behaviour of a typical section of the two storey colonnade of the Forum in Pompeii. Static analysis indicated that the failure of colonnade structures occur at higher friction angles as the weight above the structure decreases and so a sudden collapse can occur when parts of the monument are disassembled. For the dynamic analysis, the mechanical behavior of the colonnade was investigated for both harmonic and real seismic excitations. For excitations with relatively low dominant frequencies, the primary response is rocking; as the excitation frequency increases, the response becomes more complicated demonstrating both sliding and rocking movements. It was also shown that the construction methods used in ancient times, such as multi-block segmented trabeations and solid block beam, have quite significant impact on the mechanical response of the structures under static and dynamic loading. 相似文献