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1.
The influence of microcrack density on the elastic and fracture mechanical properties of Stripa granite 总被引：1，自引：0，他引：1
Ove Alm Lise-Lotte Jaktlund Kuo Shaoquan 《Physics of the Earth and Planetary Interiors》1985,40(3):161-179
Microcracks can have a strong influence on the elastic and fracture mechanical properties of rocks if they are numerous, or if they are orientated in unfavourable directions in anisotropic rocks in particular. This paper presents results from a great number of mechanical tests on Stripa granite containing various amounts of microcracks. Variations in the microcrack density were obtained by shock-heating the rock at different temperatures in the range 100–600°C for 3 h.The results presented are obtained from sound velocity measurements, uniaxial compression tests, Brazilian tests and three-point bending tests. The density of microcracks in the heated rock is studied by means of optical microscopy, SEM and differential strain analysis (DSA).Some of the calculated parameters show a maximum value for specimens heat-treated at about 100°C. The tensile strength is, for instance, substantially higher for specimens shock-heated at 100°C than for non-heated ones. Another striking feature is the initial decrease of the diameter observed in specimens heat-treated at 600°C when loaded in uniaxial compression. Both optical microscopy and DSA experiments reveal a large increase in microcracking when the heat-treatment temperature exceeds 300°C. 相似文献
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WANG Xiaoqiong XU Jianguo ZHAO Chenxu LIU Tongyuan GE Hongkui SHEN Yinghao WU Shan YU Jiayao HUANG Rongyan 《中国地震研究》2020,34(2):167-186
The premise of hydraulic fracturing is to have an accurate and detailed understanding of the rock mechanical properties and fracture propagation law of shale reservoirs. In this paper, a comprehensive evaluation of the mechanical properties of the shale oil reservoir in the south of Songliao Basin is carried out. Based on the experiments and the in-situ stress analysis, the fracture propagation law of three types of shale reservoirs is obtained, and the suggestions for fracturing are put forward. The results have shown that the fracture propagation of pure shale and low mature reservoir is easy to open along the bedding plane under compression loading, which is greatly influenced by the bedding. Sand-bearing shale is slightly better, the fractures of which are not easy to open along the bedding plane. The mechanical experimental results show that all the samples have the characteristics of low compressive strength, low Young''s modulus and strong anisotropy, indicating that the shale oil reservoir is certain plastic, which is related to its high clay mineral content and controlled by the bedding development. Compared with pure shale and low mature shale, the sand-bearing shale has less clay content and less developed bedding, which maybe the main reason for its slightly better brittleness. Overall, the expansion of hydraulic fracture is controlled by in-situ stress and bedding. Because of the development of bedding, it is easy to form horizontal fractures. Thus it is not suitable for horizontal well fracturing. Because of the high content of clay minerals, the applicability of conventional slick hydraulic fracturing fluid is poor. It is suggested to use vertical well or directional well to carry out volume fracturing. In this way, the effect of bedding can be effectively used to open and connect the bedding and form a larger fracture network. 相似文献
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The aim of this study was to investigate the effects of supercritical CO2 (scCO2) injection on the elastic and anelastic properties of sandstone at seismic and ultrasonic frequencies. We present the results of the low‐frequency and ultrasonic experiments conducted on water‐saturated sandstone (Donnybrook, Western Australia) flooded with scCO2. The sandstone was cut in the direction perpendicular to a formation bedding plane and tested in a Hoek triaxial pressure cell. During the experiments with scCO2, the low‐frequency and ultrasonic systems and the pump dispensing scCO2 were held at a temperature of 42°C. The elastic parameters obtained for the sandstone with scCO2 at seismic (0.1 Hz–100 Hz) and ultrasonic (～0.5 MHz) frequencies are very close to those for the dry rock. The extensional attenuation was also measured at seismic frequencies for the dry, water‐saturated, and scCO2‐injected sandstones. The applicability of Gassmann's fluid substitution theory to obtained results was also tested during the experiments. 相似文献
6.
Stability analysis of multi-directional anchored rock slope subjected to surcharge and seismic loads
Sanjay Kumar Shukla Md. Monir Hossain 《Soil Dynamics and Earthquake Engineering》2011,31(5-6):841-844
More than one set of anchors with different orientations can be an economical solution to completely stabilize the rock slope. In this note, a general analytical expression for the factor of safety of a multi-directional anchored rock slope (MDARS) against plane failure is derived, incorporating most of the practically occurring destabilizing forces under surcharge and seismic loading conditions. Several special cases of this expression are found to be similar to those reported in the literature. A graphical presentation shows that for any specific inclination of one set of anchors to the normal at failure plane, the variation in the inclination of the second set of anchors to the normal at failure plane, when greater than approximately 60°, does not cause a significant change in the factor of safety of the MDARS. 相似文献
7.
Mark Chapman Jeremy Sothcott Angus Ian Best Xiang‐Yang Li 《Geophysical Prospecting》2014,62(6):1238-1252
Ultrasonic (500 kHz) P‐ and S‐wave velocity and attenuation anisotropy were measured in the laboratory on synthetic, octagonal‐shaped, silica‐cemented sandstone samples with aligned penny‐shaped voids as a function of pore fluid viscosity. One control (blank) sample was manufactured without fractures, another sample with a known fracture density (measured from X‐ray CT images). Velocity and attenuation were measured in four directions relative to the bedding fabric (introduced during packing of successive layers of sand grains during sample construction) and the coincident penny‐shaped voids (fractures). Both samples were measured when saturated with air, water (viscosity 1 cP) and glycerin (100 cP) to reveal poro‐visco‐elastic effects on velocity and attenuation, and their anisotropy. The blank sample was used to estimate the background anisotropy of the host rock in the fractured sample; the bedding fabric was found to show transverse isotropy with shear wave splitting (SWS) of 1.45 ± 1.18% (i.e. for S‐wave propagation along the bedding planes). In the fractured rock, maximum velocity and minimum attenuation of P‐waves was seen at 90° to the fracture normal. After correction for the background anisotropy, the fractured sample velocity anisotropy was expressed in terms of Thomsen's weak anisotropy parameters ε, γ & δ. A theory of frequency‐dependent seismic anisotropy in porous, fractured, media was able to predict the observed effect of viscosity and bulk modulus on ε and δ in water‐ and glycerin‐saturated samples, and the higher ε and δ values in air‐saturated samples. Theoretical predictions of fluid independent γ are also in agreement with the laboratory observations. We also observed the predicted polarisation cross‐over in shear‐wave splitting for wave propagation at 45° to the fracture normal as fluid viscosity and bulk modulus increases. 相似文献
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On 24 November 1983, a major earthquake occurred at 180 km depth beneath the Banda Sea. In the focal mechanism solution the pressure axis is almost horizontal, (azimuth 191°, plunge 02°) and the tension axis nearly vertical (plunge 88°). A comparison with the foreshock-aftershock pattern suggests that shear failure took place within the north-north-westerly dipping Benioff zone by thrust faulting along a southerly dipping plane. The focal mechanism solution does not conform to the usual pattern of the tension or compression axis being roughly parallel to the dip of the Benioff zone. Consequently the faulting could not have been caused by down-dip tension or compression within a sinking slab. 相似文献
9.
Characterisation and multifaceted anisotropy assessment of Corvio sandstone for geological CO2 storage studies 
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下载免费PDF全文 Ismael Falcon‐Suarez Jacobo Canal‐Vila Jordi Delgado‐Martin Laurence North Angus Best 《Geophysical Prospecting》2017,65(5):1293-1311
We present a comprehensive characterisation of the physical, mineralogical, geomechanical, geophysical, and hydrodynamic properties of Corvio sandstone. This information, together with a detailed assessment of anisotropy, is needed to establish Corvio sandstone as a useful laboratory rock‐testing standard for well‐constrained studies of thermo–hydro–mechanical–chemical coupled phenomena associated with CO2 storage practices and for geological reservoir studies in general. More than 200 core plugs of Corvio sandstone (38.1 and 50 mm diameters, 2:1 length‐to‐diameter ratio) were used in this characterisation study, with a rock porosity of 21.7 ± 1.2%, dry density 2036 ± 32 kg m?3, and unconfined compressive and tensile strengths of 41 ± 3.28 and 2.3 ± 0.14 MPa, respectively. Geomechanical tests show that the rock behaves elastically between ～10 and ～18 MPa under unconfined conditions with associated Young's modulus and Poisson's ratio of 11.8 ± 2.8 GPa and 0.34 ± 0.01 GPa, respectively. Permeability abruptly decreases with confining pressure up to ～10 MPa and then stabilises at ～1 mD. Ultrasonic P‐ and S‐wave velocities vary from about 2.8–3.8 km s?1 and 1.5–2.4 km s?1, respectively, over confining and differential pressures between 0.1 and 35 MPa, allowing derivation of associated dynamic elastic moduli. Anisotropy was investigated using oriented core plugs for electrical resistivity, elastic wave velocity and attenuation, permeability, and tracer injection tests. Corvio sandstone shows weak transverse isotropy (symmetry axis normal to bedding) of <10% for velocity and <20% for attenuation. 相似文献
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Serpentinized ultrabasic rocks crop out at various places in the northwestern part of Turkey. They are the foundation rocks of some architecture and the ground under road bases in many areas. They are also frequently used for indoor work such as tables, shafts, pilasters, jambs for chimney pieces and ornaments of different kinds. Owing to their economic importance, in situ geophysical and geotechnical studies were conducted to determine their dynamic engineering parameters such as: P- and S-wave velocities, Poisson’s ratio, rigidity modulus, elasticity modulus, bulk modulus, natural period, safe bearing capacity, and bearing coefficient. Geophysical and geotechnical laboratory tests were performed on cylindrical specimens cored across and along the foliation planes: ultrasonic measurements of compressional pulse velocity (UPV), uniaxial compressive strength (UCS), point load index (Is(50)), and static elasticity modulus (Es); effective porosity (n), dry unit weight (DUW), and saturated unit weight (?s) sets of the rock specimens were determined. Finally, statistical correlations were performed by regression analysis to evaluate the relationships between UCS and Is(50), UPV, Es; UPV and Is(50), DUW, ?s, n, and Es. 相似文献
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K.M. Storetvedt 《Physics of the Earth and Planetary Interiors》1978,16(1):45-58
In the British Tertiary igneous province one commonly observes reversed magnetizations with an abnormally large range of inclinations. Two of the Skye lava sequences which are of Early Eocene age have been chosen to investigate why this range of inclinations exists. Various laboratory studies of the natural remanence reveal a composite palaeomagnetic record. There are two axes of magnetization present: on steeply inclined (～ 75°) and one with an intermediate inclination (～35°). There is an excess of reversed polarity components in the bulk fossil remanence of most lavas and the inclination spread seems basically caused by superposition of these components. The experimental problem of splitting the polyphase magnetization into its separate sub-components is demonstrated by many examples. It is concluded that processes of low-temperature mineral alteration (which strongly overprints the high-temperature exsolution structures) and remagnetization must have been active for a minimum time span of 20 m.y. after the original cooling of the lavas, involving both polarity inversions and a major geomagnetic axis shift in mid-Tertiary times. As a conseqence, the original TRM has probably been erased to a major extent and replaced by CRM's in subsequent times. The polar estimate based on the shallow magnetization group agree well with suggested Lower Tertiary palaeopoles from Northern Ireland and from the Faeroe Irelands. The multivectoral nature of the remanent magnetization in the Skye lavas signifies that even for geologically very young rocks it is necessary to employ much more rigorous analysis techniques than are currently being used in many palaeomagnetic laboratories. 相似文献
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Different mountain shapes in sedimentary sequences in the Canadian Rockies were enhanced by glacial erosion and have been modified postglacially by gravity-driven slope processes. Slope modification by both glacial erosion and postglaciation landslides is related to rock structure, particularly bedding dip, rock mass strength and slope geometry. Five mountain peak shapes in monoclinal sequences each fall into different ranges of bedding dips. Castellate (1) and matterhorn (2) mountains occur in sub-horizontal beds and their slopes on all sides follow combinations of bedding planes and joints. The overall slopes are generally 37 to 65° and oblique to both bedding and joints. Slopes in sub-horizontal beds may be controlled by their rock mass strength. Cuestas (3) develop in gently to moderately dipping beds. Dip slopes and steeper, normal escarpments form their cataclinal and anaclinal sides respectively, with the dihedral angle between them about 90°. Hogbacks (4) in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes. Cataclinal slopes are either dip slopes or underdip slopes but anaclinal slopes are often steepened escarpments; the dihedral angle between the slopes is usually less than 90°. Dogtooth (5) mountains occur in steeply dipping to sub-vertical beds and the dihedral angle can be as low as 60°. Slope gradients in inclined beds are closely related to landslides, whose modes are controlled by bedding dips. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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Summary The object of the present paper is to investigate magneto-elastic waves and disturbances in initially stressed conducting media. Firstly, the theory of magneto-elastic surface waves in a conducting medium under an initial uniaxial tension has been deduced and then it has been employed to investigate the particular cases of surface waves such as Rayleigh, Love and Stoneley waves. Secondly, propagation of waves in an elastic layer has been considered using the fundamental equations of motion for magneto-elastic waves in conductors under an initial uniaxial tension or compression. This is followed by the case of plane Lamb's problem in a magneto-elastic semi-space under the same initial tension. The final results obtained in the above cases are in agreement with the corresponding classical problems when the initial tension is zero and the magnetic field is absent. 相似文献
14.
本文研究了纵波垂直入射情况下两种介质分界面处的纵波反射和透射系数的频散特性,分界面上下两侧分别为层状双孔页岩介质和层状双孔砂岩介质.当纵波沿垂直于分界面的方向传播至分界面处时,会在上层双孔介质中产生三类反射纵波,在下层双孔介质中产生三类透射纵波.基于层状双孔介质的特性,给出了分界面处的六个边界条件.根据层状双孔介质的波动方程,利用平面波分析得到了纵波的反射和透射系数.结果表明：当多孔介质中存在流体时,纵波的反射和透射系数与频率相关,即存在频散现象.波致流体流动是造成纵波反射和透射系数频散的主要原因.此外,结果还表明局部流体流动引起地震频带内反射和透射系数的频散,宏观Biot流引起超声频带内反射和透射系数的频散.本文同时对岩石参数对反射和透射系数频散曲线的影响进行了研究. 相似文献
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本文主要以岩石试件切口在单轴压缩条件下的扩张来模拟大陆内部断层端部扩张型地震的孕育过程。在实验中观测了试件在外力作用下的应力-应变关系、张裂纹和剪切破坏在时间和空间上的扩展顺序,以及由此引起的声发射和纵波走时变化特征。根据实验结果讨论了由断层端部扩展引起地震的前兆——如断层蠕滑、前震迁移路径、地下水和地形变等各类地震前兆上显示的差异性,对于观测前兆和前震区与主震区的相对位置,具有一定的指导意义 相似文献
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通过超声波对单轴压缩试验中岩石扩容现象的测试,分析了超声横波在不同岩石压缩过程中的传播情况。利用超声横波的特性测出岩石在压缩的不同阶段的微裂纹发展情况和体积变化情况,进一步证明了不同岩石在单轴压缩过程中扩容的时间和程度是有所差异的。 相似文献
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Palaeomagnetic and palaeontological studies on samples withdrawn from a 250-m-long unorientated core from Reggio di Calabria, Italy (38°N, 16°E) are described. The lower 200 m of core penetrated off-shore clays and visual examination of the split sections of core indicated no obvious breaks in deposition. After alternating field demagnetization in 200 Oe the palaeomagnetic inclination log shows the Brunhes/Matuyama boundary at 110 m below which the Jaramillo and Olduvai Events within the Matuyama Epoch are identified. This interpretation of the magnetostratigraphy is supported by palaeontological evidence. The rate of accumulation of clay is estimated to have ranged between about 60 and 190 mm/kyr with an overall average through the Matuyama Epoch of about 90 mm/kyr. Assuming that this average rate continued through the Brunhes Epoch, the age of the top of the clay unit is estimated to be about 90,000 yr B.P. About 5 m from the unconformable top surface of the clay, a split sequence of reversed inclinations is interpreted as a record of the Blake Event, and the overall average deposition rate implies that its duration may have been as long as 50,000 yr. No other reversed event is recorded by the palaeomagnetic inclination log through the Brunhes Epoch, though there are four horizons where shallow positive inclinations are recorded. 相似文献
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Pore pressure changes in a geothermal reservoir, as a result of injection and/or production of water, result in changes of stress acting on the reservoir rock and, consequently, changes in the mechanical and transport properties of the rock. Bulk modulus and permeability were measured at different pressures and temperatures. An outcropping equivalent of Rotliegend reservoir rock in the North German Basin (Flechtinger sandstone) was used to perform hydrostatic tests and steady state fluid flow tests. Permeability measurements were conducted while cycling confining pressure; the dependence of permeability on stress was determined at a constant downstream pressure of 1 MPa. Also, temperature was increased stepwise from 30 to 140 °C and crack porosity was calculated at different temperatures. Although changes in the volumes of cracks are not significant, the cracks control fluid flow pathways and, consequently, the permeability of the rock. A new model was derived which relates microstructure of porosity, the stress–strain curve, and permeability. Porosity change was described by the first derivative of the stress–strain curve. Permeability evolution was ascribed to crack closure and was related to the second derivative of the stress–strain curve. The porosity and permeability of Flechtinger sandstone were reduced by increasing the effective pressure and decreased after each pressure cycle. 相似文献
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Failure Mode and Spatial Distribution of Damage in Rothbach Sandstone in the Brittle-ductile Transition 总被引：4，自引：0，他引：4
— To elucidate the spatial complexity of damage and evolution of localized failure in the transitional regime from brittle faulting to cataclastic ductile flow in a porous sandstone, we performed a series of triaxial compression experiments on Rothbach sandstone (20% porosity). Quantitative microstructural analysis and X-ray computed tomography (CT) imaging were conducted on deformed samples. Localized failure was observed in samples at effective pressures ranging from 5 MPa to 130 MPa. In the brittle faulting regime, dilating shear bands were observed. The CT images and stereological measurements reveal the geometric complexity and spatial heterogeneity of damage in the failed samples. In the transitional regime (at effective pressures between 45 MPa and 130 MPa), compacting shear bands at high angles and compaction bands perpendicular to the maximum compression direction were observed. The laboratory results suggest that these complex localized features can be pervasive in sandstone formations, not just limited to the very porous aeolian sandstone in which they were first documented. The microstructural observations are in qualitative agreement with theoretical predictions of bifurcation analyses, except for the occurrence of compaction bands in the sample deformed at effective pressure of 130 MPa. The bifurcation analysis with the constitutive model used in this paper is nonadequate to predict compaction band formation, may be due to the neglect of bedding anisotropy of the rock and multiple yield mechanisms in the constitutive model. 相似文献
20.
Naturally disaggregated specularite-bearing sandstone from the Triassic Moenkopi Formation, artificially deposited in controlled magnetic fields of ～5 × 10?2 mT, acquires a stable remanent magnetization that has systematic errors in inclination and declination. Inclinations about 12° shallower than the applied fields are produced by deposition on a horizontal surface in still water. Deposition from flowing water on a surface inclined 6–10° results in inclination errors of as much as 20°. Water flowing obliquely to the applied field results in declination errors of about 10°, with declinations systematically rotated toward the upstream direction of current flow. These experimental results indicate that specularite-bearing sediment responds to the earth's field in a manner similar to magnetite-bearing sediment, and support observational evidence for a primary magnetization of depositional origin in specularite in red beds of the Moenkopi Formation. 相似文献