基于地震波速度预测岩体物性参数模型与应用

以地震属性和钻孔测井参数为基础,依据试验数据构建数学模型,实现对煤层顶底板岩石物性参数的定量预测。通过试验拟合出纵横波波速之间关系、波速与密度的关系、动静杨氏模量、动静泊松比之间的关系,且相关程度较高。依据试验模拟结果对淮南刘庄区煤层顶底板岩石物性参数及孔隙度进行了预测。结果表明该地区的物性参数分布规律明显,且与实测结果吻合较好。模型计算与实例应用证实地震信息用于预测岩石力学参数具有可行性。     

Attenuation behaviour of tuffaceous sandstone and granite during microfracturing

Laboratory measurements of ultrasonic wave propagation in tuffaceous sandstone (Kimachi, Japan) and granite (Iidate, Japan) were performed during increasing fracturing of the samples. The fracturing was achieved by unconfined uniaxial compression up to and beyond the point of macrofracture of the specimen using a constant low strain rate. The observed variation of wave velocity (up to 40 per cent) due to the development of micro- and macrofractures in the rock is interpreted by rock models relating velocity changes to damage and crack density. The calculated density of the newly formed cracks reaches higher values for the sandstone than for the granite. Using the estimated crack densities, the attenuation behaviour is interpreted in terms of different attenuation mechanisms; that is, friction and scattering. Rayleigh scattering as described by the model of Hudson (1981 ) may explain the attenuation qualitatively if the largest plausible crack dimensions are assumed in modelling.     

Characterisation and multifaceted anisotropy assessment of Corvio sandstone for geological CO2 storage studies

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.     

A semi-empirical approach to model pressure dependence of elastic moduli in granular media accounting for variations of coordination-number and Poisson-ratio

The effective medium theory based on the Hertz–Mindlin contact law is the most popular theory to relate dynamic elastic moduli (or elastic velocities) and confining pressure in dry granular media. However, many experimental results proved that the effective medium theory predicts pressure trends lower than experimental ones and over-predicts the shear modulus. To mitigate these mispredictions, several evolutions of the effective medium theory have been presented in the literature. Among these, the model named modified grain contact theory is an empirical approach in which three parametric curves are included in the effective medium theory model. Fitting the parameters of these curves permits to adjust the pressure trends of the Poisson ratio and the bulk modulus. In this paper, we present two variations of the modified grain contact theory model. First, we propose a minor modification in the fitting function for the porosity dependence of the calibration parameters that accounts for non-linearity in the vicinity of the critical porosity. Second, we propose a major modification that reduces the three-step modified grain contact theory model to a two-step model, by skipping the calibration parameter–porosity fit in the model and directly modelling the calibration parameter–pressure relation. In addition to an increased simplicity (the fitting parameters are reduced from 10 to 6), avoiding the porosity fit permits us to apply the model to laboratory data that are not provided with accurate porosity measurements. For this second model, we also estimate the uncertainty of the fitting parameters and the elastic velocities. We tested this model on dry core measurements from literature and we verified that it returns elastic velocity trends as good as the original modified grain contact theory model with a reduced number of fitting parameters. Possible developments of the new model to add predictive power are also discussed.     

Small-strain dynamic characterization of clayey soil from the Texcoco Lake,Mexico

The area occupied by the former Texcoco Lake was part of a system of lakes inside the Basin of Mexico. The subsoil there has been studied in the past but there is still a need for more and more thorough investigations into the dynamic properties of its highly compressible clays. This paper describes the results of an experimental laboratory research in which a triaxial cell fitted with bender elements was used to measure shear wave velocities (V_s) in clay specimens from the former Texcoco Lake. Soil specimens were subjected to isotropic loading–unloading cycles and values of V_s were determined during the saturation stage and after each stress increment or decrement. Our results show that irrespective of the testing method, shear waves velocities differ in no more than 7–15%.     

泥岩、页岩声速各向异性及其影响因素分析

在实验室超声波频率下(纵波主频为700kHz、横波为250kHz)对层理发育的页岩和泥岩的各向异性进行了研究,给出了在干燥和油饱和条件下,样品不同方向上纵、横波速度以及各向异性参数随压力的变化规律. 用X 射线衍射和扫描电镜分析了样品中引起各向异性的原因,指出平行于层理定向排列的粘土矿物和微裂隙是使样品显示出强弹性各向异性的内在原因. 随着压力的增高微裂隙逐渐闭合,样品的各向异性程度减弱. 孔隙流体的存在增强了孔隙（裂隙）的刚度,减弱了各向异性随压力增大而减小的趋势.     

基于图像分析的双台面波相速度频散曲线快速提取方法

双台波形的互相关方法是面波相速度频散曲线提取的一种常用方法。传统的方法精度不高,效率较低。本文提出了一种基于图像分析的频散曲线快速提取方法,采用图像显示互相关振幅矩阵,且提出了快速追踪整条频散曲线的算法,并用Matlab编写了交互式的处理软件。基于这种方法编写的资料处理软件提高了双台相速度频散曲线提取的速度和精度,为大批量处理地震数据资料提供了坚实的软件基础。基于图像分析的方法可以更为清晰地展现出双台问的面波频散曲线的特征,对频散曲线的识别和分析也提供了更为有效的研究工具。     

An experimental study of velocities under pressure for ancient oceanic rocks

Abstract

Seismic velocities of Indus suture rock types from Dras‐Sanko‐Kargil, Kashmir Himalaya, as a function of pressure up to 10 kbar were studied. The high‐pressure measurements on the rocks reflect the depthwise increase in velocity, and in general they help in better understanding and better interpretation of the regional rocks in terms of their geological observations. An attempt has been made at correlation with ocean‐dredged samples, and it was found that the ultramafics, gabbros, and dykes are compatible with oceanic rocks and other ophiolite sequences, whereas metavolcanics are incompatible, suggesting the dismembered nature of Indus ophioli‐tes.     

Hydrological characteristics of vegetated river flows: a laboratory flume study

Abstract

Laboratory flume experiments were undertaken to measure the vertical profiles of mean flow velocity for three different flow discharges and four different stem densities of Hydrilla verticillata. The data were used to calculate three parameters, namely Manning's roughness coefficient, the Reynolds number and the Froude number. In addition, empirical equations were obtained for the vertical distribution of measured flow velocity within the transitional zone and above the plant canopy. The results show that: (a) the vertical distribution of measured flow velocity exhibits three zone profiles; (b) Manning's roughness coefficient decreases with increasing depth-averaged flow velocity; (c) the relationship between Manning's roughness coefficient and the depth-averaged flow velocity is within the smooth left inverse curve; (d) Manning's roughness coefficient significantly changes with increasing density of Hydrilla; (e) the Froude number is independent of the density of Hydrilla; and (f) both the Reynolds number and the Froude number increase with increasing depth-averaged flow velocity.

Citation Shi, J.Z., Li, Y.-H., Hughes, J.M.R., and Zhao, M., 2013. Hydrological characteristics of vegetated river flows: a laboratory flume study. Hydrological Sciences Journal, 58 (5), 1047–1058.

Editor Z.W. Kundzewicz