Shear-enhanced compaction during non-linear viscous creep of porous calcite-quartz aggregates

In this paper, we extend the previous studies of semi-brittle flow of synthetic calcite-quartz aggregates to a range of temperatures and effective pressures where viscous creep occurs. Triaxial deformation experiments were performed on hot-pressed calcite-quartz aggregates containing 10, 20 and 30 wt% quartz at confining pressure of 300 MPa, pore pressures of 50-290 MPa, temperatures of 673-1073 K and strain rates of 3.0×10⁻⁵/s, 8.3×10⁻⁵/s and 3.0×10⁻⁴/s. Starting porosity varied from 5 to 9%. We made axial and volumetric strain measurements during the mechanical tests. Pore volume change was measured by monitoring the volume of pore fluid that flows out of or into the specimen at constant pore pressure. Yield stress increased with decreasing porosity and showed a dependence on effective pressure. Thus, the yield stress versus effective pressure can be described as a yield surface with negative slope that expands with decreasing porosity and increasing strain hardening, gradually approaching the envelope of strength at 10% strain, which has a positive slope. Creep of porous rock can be modeled to first order as an isolated equivalent void in an incompressible nonlinear viscous matrix. An incremental method is used to calculate the stress-strain curve of the porous material under a constant external strain rate. The numerical simulations reproduce general trends of the deformation behavior of the porous rock, such as the yield stress decreasing with increasing effective pressure and significant strain hardening at high effective pressure. The drop of yield stress with increasing porosity is modeled well, and so is the volumetric strain rate, which increases with increasing porosity.     

用高温高压岩石蠕变实验解释岩石圈流变时存在的若干问题的讨论

由于实验条件和实际地质条件的差别,在实验温压条件下得出的变形机制。流动律和微观组构不等同于岩石圈相同温压条件下的变形机制、流动律和微观组构。因此,用高温高压蠕变实验结果直接外推解释岩石圈流变时存在若干问题。只有把实验条件、变形机制、微观组构作为一个有机的整体。去理解和认识岩石圈流变特性,才不至于产生太大的偏差。     

稀性泥石流的平均运动速度研究

泥石流的运动速度是泥石流动力学研究中最重要的参数。稀性泥石流是常见也是危害较大的泥石流类型,准确而简洁地计算稀性泥石流的运动速度非常重要。现有的稀性泥石流平均速度经验公式,在使用上和适用地区上还存在一些问题。本文通过分析一系列稀性泥石流观测资料中的体积浓度与稀性泥石流的运动速度和阻力特征的关系,得出了一个新的计算稀性泥石流平均运动速度的经验公式,该公式能适应各种类型的泥石流沟,适用于一般急流的稀性泥石流;对于缓流稀性泥石流,计算值与观测值相比偏大,但很接近;不适用于缓慢稀性泥石流。本文提出的经验公式,使用简洁,计算稳定,与其他方法计算的稀性泥石流平均运动速度很接近。该速度计算经验公式也适用于稀性泥石流堆积扇上游沟道,但对于堆积扇上的速度,计算值偏大,且越往堆积扇的下游,偏差越大。     

一种基于逾渗模型的裂隙岩石渗透系数确定方法

针对裂隙岩体提出了一种基于双重逾渗模型的渗流系数分析方法。通过变参数研究,考察了岩体中渗流和孔压分布的不均匀;根据裂隙长度的不同将岩体分为孔隙控制渗流模式和裂隙控制渗流模式。这种模型不仅能够同时考虑孔隙和裂隙的作用,而且在模拟大规模裂隙网络时更加快捷简便。     

Permeability dependence of streaming potential coefficient in porous media

In theory, the streaming potential coefficient depends not only on the zeta potential but also on the permeability of the rocks that partially determines the surface conductivity of the rocks. However, in practice, it is hard to show the permeability dependence of streaming potential coefficients because of the variation of zeta potential from sample to sample. To study permeability dependence of streaming potential, including the effects of the variation of the zeta potential and surface conductance due to the difference in mineral compositions between samples, we perform measurements on 12 consolidated samples, including natural and artificial samples saturated with 7 different NaCl solutions to determine the streaming potential coefficients. The results have shown that the streaming potential coefficients strongly depend on the permeability of the samples for low fluid conductivity. When the fluid conductivity is larger than than 0.50 S/m for the natural samples or 0.25 S/m for the artificial ceramic samples, the streaming potential coefficient is independent of permeability. This behavior is quantitatively explained by a theoretical model.     

结构附加粘滞阻尼器的抗震设计

本文结合抗震设计规范反应谱,给出了一个附加非线性流体粘滞阻尼器结构的抗震设计方法。研究了非线性阻尼器的力学特性,引入了非线性流体阻尼器的等效线性阻尼比,给出了计算最大加速度时刻附加非线性流体阻尼器结构反应的荷载组合系数,提出了按阻尼力的水平力分量与楼层剪力成正比的原则分配阻尼器阻尼系数的方法。同时给出了基于抗震规范设计反应谱附加非线性阻尼器结构的设计流程,通过一个算例说明了使用该方法设计附加非线性粘滞阻尼器结构的全过程。算例分析表明,这种设计方法适合于手算,便于设计人员掌握,在初步设计阶段可以快速、有效地设计满足给定性能水平的附加非线性流体阻尼器体系。     

附设黏滞阻尼器的传统风格建筑混凝土梁-柱节点动力循环荷载累积损伤分析

为研究附设黏滞阻尼器的传统风格建筑混凝土梁-柱节点地震损伤演化规律,进行6个该类型构件的动力荷载试验,并分别采用位移型、能量型及位移-能量混合型损伤模型对其进行全过程评价,采用Park-Ang模型分析试件黏滞阻尼器型号、试件类型等因素对混凝土传统风格建筑梁柱节点损伤行为的影响。研究结果表明：附设黏滞阻尼器可显著提升传统风格建筑节点的承载能力、延性性能及耗能能力,结构的抗震性能得到较大幅度的提升;Park-Ang损伤模型与Banon损伤模型适用于传统风格建筑节点损伤演化规律的描述,建议对该类型节点的损伤规律表征选用该损伤模型。黏滞阻尼器型号可在一定程度上影响传统风格建筑的损伤演化发展;设计阻尼力大的试件虽然延性有所提高,但受荷过程中累积损伤也较大。     

裂隙土等效连续介质的渗透张量及表征单元体积

裂隙土的渗透特性是裂隙土边坡稳定性分析中重要的参数。文中通过分别考虑随机裂隙网络和土体本身的渗透性,推导裂隙土的渗透系数,并用张量的形式表示渗透系数的各向异性。同时建立了确定裂隙土表征单元体积的准则,为应用等效连续介质模型提供了基础。结果表明裂隙土的渗透系数大于裂隙网络和土体的渗透系数,其渗透方向取决于裂隙网络的渗透方向。算例中裂隙土的表征单元体积大约是裂隙长度平均值的5倍。     

低孔渗砂岩孔隙结构分类方法研究

低孔渗砂岩储层孔隙结构复杂,在二维与三维空间中具有较强非均质性,对储集空间的测井响应有极大影响。而压汞曲线、核磁T₂谱、铸体薄片3种资料在一定程度上各自反映了孔隙结构的不同特征,本文分别提取3种资料的微观孔隙结构参数进行相关性分析,最终分别利用主成分分析-模糊均值聚类方法实现孔隙结构分类,其分类结果压汞曲线分形法所得一致。     

多矿物岩石流变规律的研究进展及存在问题

总结了近年来由多种矿物组成的岩石的流变规律的研究，阐述了多矿物岩石流变性质研究的意义和进展，再从实验和理论两个方面，详细论述了目前最具代表性的三种理论模型，算术平均方法、几何平均方法和能量极小方法，最后，指出这方面研究仍然存在的问题和进一步研究的方向。     

Permeability and degassing of dome lavas undergoing rapid decompression: An experimental determination

The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rocks permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. Using a modified shock-tube-based fragmentation bomb (Alidibirov and Dingwell 1996a,b; Spieler et al. 2003a), we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample. Two pressure transducers record the pressure signals above and below the sample. A transient 1D filtration code has been developed to calculate permeability using the experimental decay curve of the lower pressure transducer. Additionally an analytical steady-state method to achieve permeability is presented as an alternative to swiftly predict the sample permeability in a sufficiently precise manner. Over 100 permeability measurements have been performed on samples covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Our preferred interpretation of the results is a combination of two different, but overlapping effects. We propose that at low porosities, gas escape occurs predominantly through microcracks or elongated micropores and therefore could be described by simplified forms of Kozeny–Carman relations (Carman 1956) and fracture flow models. At higher porosities, the influence of vesicles becomes progressively stronger as they form an increasingly connected network. Therefore, a model based on the percolation theory of fully penetrable spheres is used, as a first approximation, to describe the permeability-porosity trend. In the data acquired to date it is evident, that in addition to the porosity control, the samples bubble size, shape and distribution strongly influence the permeability. This leads to a range of permeability values up to 2.5 orders of magnitude at a given porosity.     

Laboratory measurement of compaction-induced permeability change in porous rocks: Implications for the generation and maintenance of pore pressure excess in the crust

Permeability exerts significant control over the development of pore pressure excess in the crust, and it is a physical quantity sensitively dependent on the pore structure and stress state. In many applications, the relation between permeability and effective mean stress is assumed to be exponential and that between permeability and porosity is assumed to be a power law, so that the pressure sensitivity of permeability is characterized by the coefficient and the porosity sensitivity by the exponent . In this study, we investigate experimentally the dependence of permeability on pressure and porosity in five sandstones with porosities ranging from 14% to 35% and we review published experimental data on intact rocks, unconsolidated materials and rock fractures. The laboratory data show that the pressure and porosity sensitivities differ significantly for different compaction mechanisms, but for a given compaction mechanism, the data can often be approximated by the empirical relations. The permeabilities of tight rocks and rock joints show relatively high pressure sensitivity and low porosity sensitivity. A wide range of values for and have been observed in relation to the mechanical compaction of porous rocks, sand and fault gouge, whereas the porosity sensitivity for chemical compaction processes is often observed to be given by 3. We show that since the ratio / corresponds to the pore compressibility, the different dependences of permeability on porosity and pressure are related to the pore structure and its compressibility. Guided by the laboratory data, we conduct numerical simulations on the development of pore pressure in crustal tectonic settings according to the models ofWalder andNur (1984) andRice (1992). Laboratory data suggest that the pressure sensitivity of fault gouge is relatively low, and to maintain pore pressure at close to the lithostatic value in the Rice model, a relatively high influx of fluid from below the seismogenic layer is necessary. The fluid may be injected as vertically propagating pressure pulses into the seismogenic system, andRice's (1992) critical condition for the existence of solitary wave is shown to be equivalent to >1, which is satisfied by most geologic materials in the laboratory. Laboratory data suggest that the porosity sensitivity is relatively high when the permeability is reduced by a coupled mechanical and chemical compaction process. This implies that in a crustal layer, pore pressure may be generated more efficiently than cases studied byWalder andNur (1984) who assumed a relatively low porosity sensitivity of =2.     

Reflection and refraction of plane harmonic waves at an interface between elastic solid and porous solid saturated by viscous liquid

A general solution of Biot's field equations governing small motions of a porous solid saturated by viscous liquid is employed to study the reflection and refraction at the interface between an elastic solid and a liquid-saturated porous solid. The incident wave is assumed to be plane and homogeneous, propagating through the isotropic elastic solid. The poroelastic solid is considered to be a dissipative one. Amplitude and energy ratios are computed numerically for a particular model. With first-order corrections for the porosity of solid and viscosity of liquid, the limiting cases of low and high frequencies are computed.     

基于气体包裹体模型的低孔低渗储层声波速度研究

随着石油勘探工业的持续发展和技术水平的日益提高,低孔低渗油气藏已成为我国油气勘探开发的重要领域之一,但是该类油气藏的储层岩石物理关系复杂,对其评价也相对较难。本文针对中深层气藏低孔低渗储层评价存在的困难,采用修正的White气体包裹体模型开展岩石物理研究。首先对气体包裹体模型进行分析,得到纵横波速度的计算公式,进而理论计算并分析纵横波速度与孔隙度、饱和度、压力及温度参数的变化关系,最后结合岩心实验对理论计算结果进行了验证。研究结果表明基于气体包裹体模型的理论计算结果与实测数据吻合较好,可以较好地为低孔低渗复杂储层声波速度测量及解释提供技术支持。     

基于核磁共振双截止值的致密砂岩渗透率评价新方法

对比分析致密砂岩岩心在完全含水状态和束缚水状态下的核磁共振T₂谱,明确了致密砂岩孔隙中流体的赋存状态和渗流规律,指出常规核磁共振方法预测渗透率的局限性并提出核磁共振双截止值的概念.基于核磁共振双截止值,将储集空间细分为完全可动、完全束缚、部分可动等三部分,分析不同孔隙组分对渗透率的影响,并应用三组分法建立了核磁共振渗透率表征新模型.研究表明：致密砂岩渗透率与完全可动流体饱和度、部分可动流体T₂几何平均值、核磁孔隙度成正比,与完全束缚流体饱和度成反比.在此基础上,结合完全含水核磁共振T₂谱的二阶差分得到了双截止值的自适应确定方法,可以连续地计算储层双截止值.将该研究成果应用于生产实践,渗透率计算精度有较大的提高.

     

基于向量式有限元的黏滞阻尼减震结构抗竖向连续倒塌动力反应分析

向量式有限元是以向量力学为基础的一种新的结构分析方法,在处理结构大变形等复杂行为时具有较大的优势。基于向量式有限元理论建立了黏滞阻尼单元,对附加黏滞阻尼器的平面钢框架结构进行了抗竖向连续倒塌动力分析,结合拆除构件法,采用MATLAB编制可以考虑初始变形的瞬时卸载法程序,实现结构在构件拆除前的静力分析和构件拆除后动力分析的全过程统一。研究了阻尼器布置位置和参数在结构抗竖向连续倒塌中的性能需求,以失效点竖向位移时程曲线、梁端转角、动力放大系数和结构塑性铰分布为参考指标,对比分析布置阻尼器前后钢框架结构的抗连续倒塌能力。结果表明向量式有限元是一种研究结构竖向连续倒塌动力响应的有效方法,合理布置阻尼器能够有效控制剩余结构的变形和振动,降低构件内力,减少塑性铰个数,较大地提高结构的抗竖向连续倒塌能力。     

Quantification of Exhumation from Sonic Velocity Data, Cooper Basin, Australia, and Implications for Hydrocarbon Exploration

Exhumation (defined as rock uplift minus surface uplift) in the Cooper Basin of South Australia and Queensland has been quantified using the compaction methodology. The sonic log, which is strongly controlled by the amount of porosity, is an appropriate indicator of compaction, and hence is used for quantifying exhumation from compaction. The traditional way of estimating exhumation based on the degree of overcompaction of a single shale unit has been modified and five units ranging in age from Permian to Triassic have been analysed. The results reveal that exhumation increases eastwards from the South Australia into the Queensland sector of the basin. The results show that exhumation in Late Triassic – Early Jurassic times, after the Cooper Basin deposition, seems to be 200–400 m higher than exhumation in Late Cretaceous – Tertiary times, after the Eromanga Basin deposition. This study has major implications for hydrocarbon exploration. Maturation of source rocks will be greater for any given geothermal history if exhumation is incorporated in maturation modelling. Exhumation values can also be used to improve porosity predictions of reservoir units in undrilled targets.     

Discrete Element Modeling of Stress and Strain Evolution Within and Outside a Depleting Reservoir

Stress changes within and around a depleting petroleum reservoir can lead to reservoir compaction and surface subsidence, affect drilling and productivity of oil wells, and influence seismic waves used for monitoring of reservoir performance. Currently modeling efforts are split into more or less coupled geomechanical (normally linearly elastic), fluid flow, and geophysical simulations. There is evidence (from e.g. induced seismicity) that faults may be triggered or generated as a result of reservoir depletion. The numerical technique that most adequately incorporates fracture formation is the DEM (Discrete Element Method). This paper demonstrates the feasibility of the DEM (here PFC; Particle Flow Code) to handle this problem. Using an element size of 20 m, 2-D and 3-D simulations have been performed of stress and strain evolution within and around a depleting reservoir. Within limits of elasticity, the simulations largely reproduce analytical predictions; the accuracy is however limited by the element size. When the elastic limit is exceeded, faulting is predicted, particularly near the edge of the reservoir. Simulations have also been performed to study the activation of a pre-existing fault near a depleting reservoir.     

The Temporal Evolution of Shear wave Splitting and Geoelectrical Anisotropy During Yongdeng Earthquake

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