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1.
Poro‐mechanical and thermo‐mechanical processes change the fracture aperture and thus affect the water flow pattern in the fracture during the cold water injection into enhanced geothermal systems (EGS). In addition, the stresses generated by these processes contribute to the phenomenon of reservoir seismicity. In this paper, we present a three‐dimensional (3D) partially coupled poro‐thermoelastic model to investigate the poroelastic and thermoelastic effects of cold water injection in EGS. In the model, the lubrication fluid flow and the convective heat transfer in the fracture are modeled by the finite element method, while the pore fluid diffusion and heat conductive transfer in the reservoir matrix are assumed to be 3D and modeled by the boundary integral equation method without the need to discretize the reservoir. The stresses at the fracture surface and in the reservoir matrix are obtained from the numerical model and can be used to assess the variation of in situ stress and induced seismicty with injection/extraction. Application of the model shows that rock cooling induces large tensile stresses and increases fracture conductivity, whereas the rock dilation caused by fluid leakoff decreases fracture aperture and increases compressive total stresses around the injection zone. However, increases in pore pressure reduce the effective stresses and can contribute to rock failure, fracture slip, and microseismic activity. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
堆积层滑坡的岩土体渗透系数具有一定的不确定性,且渗透系数是饱和-非饱和渗流分析的重要参数,开展考虑其空间变异性的库岸堆积层滑坡渗流变形分析具有重要意义。以三峡库区中的白水河滑坡为研究对象,基于地面核磁共振技术获取的岩土体渗透系数,分析滑坡体渗透系数的空间变异特征,采用半变异函数方法求得滑坡体渗透系数的竖直波动范围,在此基础上建立渗透系数的非平稳随机场模型。以非侵入式随机有限元的方式开展库水升降两种工况下不确定模型与确定模型的流固耦合模拟,分析两种模型的渗流场、位移变形特征及其差异。结果表明：相比于确定模型,不确定模型孔压改变的滞后性更为明显,且库水下降工况下整体的变形更大,若忽略滑体渗透系数的非平稳空间变异特征将会低估滑坡的实际变形。 相似文献
3.
In the present paper, a new stochastic framework is introduced to decompose random variables. This decomposition method is
shown to better capture and reflect the medium heterogeneity for multimodal porous media than the classical Reynolds decomposition
does. In particular, with this decomposition method, the variance of log conductivity is decomposed into two parts. The first
one measures the mean differences of log conductivity across different units having high contrasting conductivity. The second
part measures the variation of log conductivity arisen within individual units. Based on this localized decomposition, a new
stochastic model is proposed for flow in a highly heterogeneous porous media. This stochastic model shall produce much sharper
approximations under the assumption that only the second part of the variance of log conductivity is small. Therefore, the
proposed model can partially overcome the assumption of small composite variance for log conductivity in current theory for
both flow and transport. 相似文献
4.
The formulation of macroscopic poroelastic behavior of a jointed rock is investigated within the framework of a micro–macro approach. The joints are modeled as interfaces, and their behavior is modeled by means of generalized poroelastic state equations. Starting from Hill's lemma extended for a jointed medium and extending the concept of strain concentration to relate the joint displacement jump to macroscopic strain, the overall poroelastic constitutive equations for the jointed rock are formulated. The analysis emphasizes the main differences and similarities of the resulting behavior with respect to that characterizing ordinary porous media. It is shown that, unlike ordinary porous media, conditions on the poroelastic parameters of joints are required for the macroscopic drained stiffness to entirely define the poroelastic behavior. This is achieved, for instance, if the joint network is characterized by a unique Biot coefficient. Extension of the analysis to non‐linear poroelasticity is also outlined. Finally, the theoretical formulation is applied to two particular cases of jointed rock for which explicit expressions of the overall poroelastic parameters are derived. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
The relationship between seismic and aseismic motions induced by forced fluid injections 总被引：1，自引：1，他引：0
Fran?ois Henri Cornet 《Hydrogeology Journal》2012,20(8):1463-1466
The injection of fluid into a rock mass results in variations of effective stresses that sometimes generate induced seismicity. These effective stress field variations depend on the diffusion process, which depends, in turn, on the magnitude of the pore pressure variation relative to the total stress. Four diffusion mechanisms are distinguished: diffusion through a poroelastic rock mass, and diffusion in preferential directions controlled either by slip along preexisting fractures, or by the development of fresh shear zones, or by hydraulic fracturing. More importantly, in some instances, this diffusion process also generates non-seismic motions that, in turn, influence the seismic activity, in particular when injection stops. 相似文献
6.
岩体节理表面几何特性描述 总被引：1，自引：0，他引：1
岩体节理表面几何特征对岩体变形、刚度、剪切强度和水渗导性有重要影响,一般用节理粗糙度系数（ＪＲＣ）、节理吻合系数（ＪＭＣ）来描述。本文用节理表面分维（ＪＳＦ）来描述节理表面形态的复杂性,为节理表面几何特征描述提供了一个新的方法。 相似文献
7.
Steven B. Meyerhoff Reed M. Maxwell Wendy D. Graham John L. Williams III 《Hydrogeology Journal》2014,22(6):1329-1343
Subsurface heterogeneity is one of the largest sources of uncertainty associated with saturated hydraulic conductivity. Recent work has demonstrated that uncertainty in hydraulic conductivity can impart significant uncertainty in runoff generation processes and surface-water flow. Here, the role of site characterization in reducing hydrograph prediction bias and uncertainty is demonstrated. A fully integrated hydrologic model is used to conduct two sets of stochastic, transient simulation experiments comprising different overland flow mechanisms: Dunne and Hortonian. Conditioning hydraulic conductivity fields using values drawn from a simulated synthetic control case are shown to reduce both mean bias and variance in an ensemble of conditional hydrograph predictions when compared with the control case. The ensemble simulations show a greater reduction in uncertainty in the hydrographs for Hortonian flow. The conditional simulations predict surface ponding and surface pressure distributions with reduced mean error and reduced root mean square error compared with unconditional simulations. Uncertainty reduction in Hortonian and Dunne flow cases demonstrates different temporal signals, with more substantial reduction achieved for Hortonian flow. 相似文献
8.
The paper presents a micromechanical approach to describe the failure of low-permeability brittle rocks as a multiscale fracturing process based on a poroelastic microcrack-damage model. Failure is formulated deep down at the fine pore scale as a material degradation phenomenon driven by microcrack growth that also impacts upon hydromechanical properties. A set of damage tensors describes the effect of dual-scale porosities (nanopores and microcracks) on both the hydraulic and poroelastic rock properties. Essentially, the multiscale model reconstructs the coupling effect of hydromechanical forces at the continuum level from the ground up through the upscaling of multiphase interactions at the fundamental structural level of the material. As a result, many macroscopic characteristics emerge naturally such as friction angle, fracture properties, and most importantly, Biot's coefficient taking on a tensorial form that is generally anisotropic. The model is validated within the framework of finite elements to illustrate various baseline constitutive features such as the effect of microcrack growth on the nonlinear stress-strain response and the induced anisotropy in the context of lab experimental tests and boundary value problems. Heterogeneities of the rock samples were incorporated by choosing material properties to be stochastic following Weibull and lognormal distributions. Numerical results appropriately replicated typical experimental observations where fracture localization and propagation are shown to be a multiscale phenomenon emerging from microcrack growth and coalescence at the microscale, with concomitant enhancement in fluid conductivity. 相似文献
9.
碎屑岩储层渗透率分布非均性是直接影响油气开采效果的客观因素。笔者认为储层渗透率分布具有分形特征，其分维值介于２与３之间，实例研究表明，分维能描述透率分布的非均匀性，其值随非均匀程度增加而增加。分维还能反映沉积能量分布和成岩作用对渗透率分布的影响。分维将是一个研究碎屑岩层渗透率分布的数学和成因特征的重要参数。研究分维与石油工程参数的关系具有现实意义。 相似文献
10.
在地下水污染模拟预报中,弥散参数是很难确定的一个模型参数。因实验室小尺度弥散规律一般不能用于大尺度弥散过程,而野外示踪试验却耗资大、周期长,限制了其实用性。文中利用随机数值模拟手段、基于随机理论的蒙特卡罗方法及序贯高斯模拟技术来生成渗透系数随机场,并研究渗透系数对数场的方差、相关长度以及变异函数类型在不同尺度上对纵向弥散度的影响,进而建立纵向弥散度与随机分布渗透系数场的方差和相关长度的统计定量关系,并与Gelhar理论计算结果进行比较。数值模拟结果表明,经过一定迁移距离后纵向弥散度与随机分布渗透系数对数场的方差和相关长度具有良好的线性统计关系,与Gelhar理论公式表达的关系类型类似。但对于较大的方差,纵向弥散度模拟结果明显大于Gelhar理论计算值,而对于较大相关长度在迁移距离不很大时,纵向弥散度模拟结果明显小于Gelhar理论计算值。本研究可为野外大尺度地下水污染预报模型中水动力弥散参数的确定提供方法借鉴。 相似文献
11.
Stefan Bachu 《Tectonophysics》1991,190(2-4):299-314
Heterogeneity is present in geological sedimentary structures at all scales from pore to basin, and its distribution has an impact on transport processes such as heat and fluid flow. The rock masses at any scale need to be characterized by their effective properties at that scale, based on the individual characteristics of the heterogeneous porous medium. The effective thermal and hydraulic conductivity of sediments characterized by a stochastic distribution of heterogeneity is studied using an inverse approach based on numerical experiments. The simulations, covering a large range of conductivity contrasts, are carried out for actual core-scale cases of shale clasts in a sand matrix, and on a diagrammatic cross-section through a clastic sedimentary group at the basin scale.
The effective conductivity depends primarily on the heterogeneity fraction and on the conductivity contrast between heterogeneities and the embedding matrix, a dependency which can be described by a generalized weighted mean model. This model is better suited to estimate the effective conductivity at any scale than other models like the self-consistent, or any of the arithmetic, geometric or harmonic averages. The effective conductivity has an anisotropic character although the individual components are homogeneous and isotropic. The variation in effective conductivity is significant even for small conductivity contrasts, like in heat flow processes, and exhibits an asymptotic behaviour for large conductivity contrasts characteristic of fluid flow processes. The effective conductivity has a second-order dependence on such heterogeneity characteristics as shape, aspect ratio, orientation, and distribution. Depending on these characteristics, the bounds of effective conductivity values can be narrowed further from the extreme bounds expressed by the arithmetic and harmonic averages. 相似文献
12.
北塘水库库底地层渗透系数的随机特性分析 总被引：4，自引：0，他引：4
为研究渗透系数的随机分布特征,以滨海平原水库也是南水北调调节及事故备用水库的北塘水库库底地层为研究对象,通过野外取样、室内达西渗透实验和颗粒分析实验等手段,获取了库底地层渗透系数的两组数据及其空间分布,借助于SPSS软件的P—P图以及单样本K-S检验,对渗透系数的空间随机分布进行了分析。结果表明,与正态分布相比较,北塘水库库底地层渗透系数更接近对数正态分布,这为库区渗漏量计算的可靠性分析、库底沉积物渗透系数的空间变异特征分析等奠定了基础。 相似文献
13.
14.
层状可压缩岩基三维固结问题的状态空间解 总被引：1，自引：0，他引：1
采用状态空间法求解层状可压缩岩基的三维固结问题。首先从直角坐标系下考虑可压缩性的三维Biot固结问题的控制方程出发,通过Laplace-Fourier变换得到状态空间方程,解此方程并通过Cayley-Hamilton定理,得到单层可压缩岩基三维固结问题的传递矩阵;然后利用传递矩阵法,结合层间连续性条件和边界条件,得到了层状可压缩岩基三维固结问题在积分变换域内的解答;最后应用Laplace-Fourier逆变换技术,得到层状可压缩岩基三维固结问题在物理域内的理论解答。编制了相应的计算程序,进行了数值计算与分析,证明了压缩性对岩基固结问题的影响 相似文献
15.
Fushen Liu 《国际地质力学数值与分析法杂志》2020,44(12):1634-1655
The paper presents an embedded strong discontinuity approach to simulate single hydraulic fracture propagation in the poroelastic medium under plane-strain conditions. The method enriches the strain field with the discontinuous deformation mode and allows the fracture to be modeled inside elements. The Mode-I fracture initiation and propagation are described by the trilinear cohesive law, which is implemented by the penalty method. The enhanced permeability inside the fractured elements is dependent on the fracture aperture. Hydraulic fracture propagation is driven by the high pressure gradient near the fracture. Fluid transfer between the fracture and bulk rock is automatically captured within the poroelastic framework. The numerical framework is verified by the comparisons with the asymptotic analytical solutions for single hydraulic fracture propagation. 相似文献
16.
借助于Biot 波动理论和弹性波的传播理论,采用复变函数和多级坐标法,对半空间饱和土中圆形衬砌结构对弹性稳态压缩波的散射问题进行求解和分析。利用一个半径很大的圆弧来逼近半空间直边界,将待解问题转化为稳态弹性压缩波在一个大圆孔和一个弹性衬砌结构的散射问题。通过引入势函数,将饱和土的Biot波动方程和衬砌的弹性波动方程解耦成Helmholtz 方程,借助复变函数级数展开便可以预先写出该组Helmholtz方程的通解。然后,通过引用复变量,把饱和土和衬砌结构中的应力、位移及孔压用设定的势函数表示出来,再利用半空间饱和土和衬砌结构的连续性条件和近似直边界的圆弧边界和衬砌内边界的边界条件求解出该组势函数的特解。最后,利用势函数的特解,得到饱和土中的位移,应力和孔压及衬砌结构的位移和应力;变换不同的参数求解衬砌结构内外边界的动应力和孔压的集中系数,通过对算例结果的分析得出一系列有益的结论。 相似文献
17.
水平简谐荷载作用下层状饱和土体动力响应 总被引：1，自引：0，他引：1
根据Biot波动理论,采用传递、反射矩阵（TRM）方法研究了水平简谐荷载作用下层状饱和土动力响应问题。由Helmholtz矢量分解求出基本解,再利用TRM法推导了层状饱和土动力响应,并由数值Hankel逆变换得到层状土地基位移、应力及孔压在空间域内的解。利用计算结果与已有结果相比较,二者相吻合,验证了算法的正确性。算例分析表明,水平简谐荷载作用在有软弱夹层的层状土体中比均质土中具有更显著的动力响应,尤其是软夹层上下有硬土层时,会引起软弱夹层土体孔隙水压升高、位移幅值增大、土体波动性增强;而荷载作用硬夹层及夹层上下有软土层时,情况则相反。 相似文献
18.
19.
This work presents the application of a Monte Carlo simulation method to perform an statistical analysis of transient variably saturated flow in an hypothetical random porous media. For each realization of the stochastic soil parameters entering as coefficients in Richards' flow equation, the pressure head and the flow field are computed using a mixed finite element procedure for the spatial discretization combined with a backward Euler and a modified Picard iteration in time. The hybridization of the mixed method provides a novel way for evaluating hydraulic conductivity on interelement boundaries. The proposed methodology can handle both large variability and fractal structure in the hydraulic parameters. The saturated conductivity K
s and the shape parameter vg in the van Genuchten model are treated as stochastic fractal functions known as fractional Brownian motion (fBm) or fractional Gaussian noise (fGn). The statistical moments of the pressure head, water content, and flow components are obtained by averaging realizations of the fractal parameters in Monte Carlo fashion. A numerical example showing the application of the proposed methodology to characterize groundwater flow in highly heterogeneous soils is presented. 相似文献
20.
根据给定渗透系数、孔隙度以及吸附系数的概率分布,采用顺序高斯模拟生成相关的多参数随机场的实现,作为地下水流和溶质运移模型的输入参数,对污染物浓度进行随机分析。研究结果表明,与仅考虑渗透系数空间变异性相比,考虑相关的多参数空间变异性导致污染羽的扩散程度有显著不同。当孔隙度与渗透系数呈正相关关系时,会减少污染羽的扩散程度,反之,当孔隙度与渗透系数为负相关关系时,会加剧污染羽的扩散程度。吸附系数也是如此。在考虑吸附系数的空间变异性之后,污染羽的分布表现出拖尾现象。同时考虑渗透系数、孔隙度以及吸附系数空间变异性时,孔隙度非均质性对溶质运移的影响较吸附系数非均质性的影响更大。 相似文献