Nonlinear two-point flux approximation for modeling full-tensor effects in subsurface flow simulations     

Yuguang Chen  Bradley T. Mallison  Louis J. Durlofsky 《Computational Geosciences》2008,12(3):317-335

Subsurface flow models can exhibit strong full-tensor anisotropy due to either permeability or grid nonorthogonality effects. Upscaling procedures, for example, generate full-tensor effects on the coarse scale even for cases in which the underlying fine-scale permeability is isotropic. A multipoint flux approximation (MPFA) is often needed to accurately simulate flow for such systems. In this paper, we present and apply a different approach, nonlinear two-point flux approximation (NTPFA), for modeling systems with full-tensor effects. In NTPFA, transmissibility (which provides interblock connections) is determined from reference global flux and pressure fields for a specific flow problem. These fields can be generated using either fully resolved or approximate global simulations. The use of fully resolved simulations leads to an NTPFA method that corresponds to global upscaling procedures, while the use of approximate simulations gives a method corresponding to recently developed local–global techniques. For both approaches, NTPFA algorithms applicable to both single-scale full-tensor permeability systems and two-scale systems are described. A unified framework is introduced, which enables single-scale and two-scale problems to be viewed in a consistent manner. Extensive numerical results demonstrate that the global and local–global NTPFA techniques provide accurate flow predictions over wide parameter ranges for both single-scale and two-scale systems, though the global procedure is more accurate overall. The applicability of NTPFA to the simulation of two-phase flow in upscaled models is also demonstrated.  相似文献   

Permeability of 3D discontinuity networks: New tensors from boundary-conditioned homogenisation     

A. Pouya  O. Fouché 《Advances in water resources》2009

Two equivalent permeability tensors are defined for 3D heterogeneous media, K^p${\mathbf{K}}^p$ and K^q${\mathbf{K}}^q$, valid respectively for linear pressure and constant flux conditions at the block boundary. Both tensors are symmetric and positive-definite and the second one produces lower magnitude of directional permeability than the first one. These tensors only depends upon the internal block structure and 3D distribution of the local permeability values. On this basis, we develop first a straightforward method for evaluating the coefficients of the 2D tensor for the problem of flow through fracture traces in a cross-section, subject to linear pressure conditions. A quartzite rock mass is used as an example to illustrate this method. Then, an approximated method is proposed to build up the 3D permeability tensor of the fractured block from the ellipses within cross-sections in varied orientations.  相似文献   

Steady state heat transport in 3D heterogeneous porous media     

Juan J. Hidalgo  Jesús Carrera  Marco Dentz 《Advances in water resources》2009

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张渤带陆地段现代构造应力场的非均匀特征   总被引：6，自引：1，他引：5  

张红艳  谢富仁  崔效锋  李瑞莎 《中国地震》2009,25(3)

依据活动构造展布及震中分布等情况,将张渤带(张家口-渤海断裂带)陆地段及邻近地区划分为6个应力区,利用格点尝试法计算了1967～2006年间这6个分区内的529个震源机制解.结果显示,6个分区的应力结构较为一致,均为走滑型应力结构;但在应力方向上有明显不同,其应力主轴方向有由西北端的NEE向至东南端的近EW向呈顺时针旋转的趋势.此外,以1976年唐山地震与1998年张北地震为时间界限,计算了张渤带陆地段3个构造交汇段(即张北-怀来段、南口-三河段、天津-塘沽段,简称西段、中段、东段)上的地震震源机制解及各构造段在不同时段的平均主应力轴分布,得到了应力场随时间的变化特征.其中,西段与中段的构造应力场变化复杂,其应力主轴方向在唐山地震后经调整已基本回复至唐山地震前的状态;而东段的平均应力主轴呈顺时针旋转,目前仍为近EW向.张渤带陆地段现代构造应力场的时空非均匀变化特征可能与周边块体的相互作用及两次中强地震(唐山地震与张北地震)有关.  相似文献   

Patterns and dynamics of river–aquifer exchange with variably-saturated flow using a fully-coupled model     

S. Frei  J.H. Fleckenstein  S.J. Kollet  R.M. Maxwell 《Journal of Hydrology》2009,375(3-4):383-393

The parallel physically-based surface–subsurface model PARFLOW was used to investigate the spatial patterns and temporal dynamics of river–aquifer exchange in a heterogeneous alluvial river–aquifer system with deep water table. Aquifer heterogeneity at two scales was incorporated into the model. The architecture of the alluvial hydrofacies was represented based on conditioned geostatistical indicator simulations. Subscale variability of hydraulic conductivities (K) within hydrofacies bodies was created with a parallel Gaussian simulation. The effects of subscale heterogeneity were investigated in a Monte Carlo framework. Dynamics and patterns of river–aquifer exchange were simulated for a 30-day flow event. Simulation results show the rapid formation of saturated connections between the river channel and the deep water table at preferential flow zones that are characterized by high conductivity hydrofacies. Where the river intersects low conductivity hydrofacies shallow perched saturated zones immediately below the river form, but seepage to the deep water table remains unsaturated and seepage rates are low. Preferential flow zones, although only taking up around 50% of the river channel, account for more than 98% of total seepage. Groundwater recharge is most efficiently realized through these zones. Subscale variability of K_sat slightly increased seepage volumes, but did not change the general seepage patterns (preferential flow zones versus perched zones). Overall it is concluded that typical alluvial heterogeneity (hydrofacies architecture) is an important control of river–aquifer exchange in rivers overlying deep water tables. Simulated patterns and dynamics are in line with field observations and results from previous modeling studies using simpler models. Alluvial heterogeneity results in distinct patterns and dynamics of river–aquifer exchange with implications for groundwater recharge and the management of riparian zones (e.g. river channel-floodplain connectivity via saturated zones).  相似文献   

Visualization and Analysis of Mixing Dynamical Properties in Convecting Systems with Different Rheologies     

A. A. Ten  D. A. Yuen  Yu. Yu. Podladchikov 《Visual Geosciences》1999,4(1):1-15

We analyzed and compared the mixing properties of 2-D mantle convection models. Two rheologically different models, Newtonian and non-Newtonian (power-law), were considered with both the line and field methods. The line method is based on monitoring of passive particles joined into lines, while the field method relies on the advection of a passive scalar field. Both visual and quantitative estimates revealed that the efficiency of the Newtonian mixing is greater than the non-Newtonian. A heterogeneity placed in the non-Newtonian convection forms horizontal structures, which may persist for at least 1 Ga on the upper-mantle scale. In addition, the non-Newtonian medium reveals a lesser amount of stretching of the lines than the Newtonian material. The rate of the Newtonian stretching fits well with an exponential dependence with time, while the non-Newtonian rheology shows the stretching rate close to a power-law dependence with time. In the Newtonian medium the heterogeneity is reorganized into two unstable vertical columns, while the non-Newtonian mixing favors horizontal structures. In the latter case, these structures are sufficiently stable in both the temporal and spatial planes to explain the mantle geochemical and geophysical heterogeneities. Due to the non-linear character of power-law rheology, the non-Newtonian medium offers a “natural” scale-dependent resistance to deformation, which prevents efficient mixing at the intermediate length scales.  相似文献   

Spectral heterogeneity on Phobos and Deimos: HiRISE observations and comparisons to Mars Pathfinder results     

N. Thomas  R. Stelter  A. Ivanov  N.T. Bridges  K.E. Herkenhoff  A.S. McEwen 《Planetary and Space Science》2011,59(13):1281-1292

The High-Resolution Imaging Science Experiment (HiRISE) onboard Mars Reconnaissance Orbiter (MRO) has been used to observe Phobos and Deimos at spatial scales of around 6 and 20 m/px, respectively. HiRISE (McEwen et al., JGR, 112, CiteID E05S02, DOI: 10.1029/2005JE002605, 2007) has provided, for the first time, high-resolution colour images of the surfaces of the Martian moons. When processed, by the production of colour ratio images for example, the data show considerable small-scale heterogeneity, which might be attributable to fresh impacts exposing different materials otherwise largely hidden by a homogenous regolith. The bluer material that is draped over the south-eastern rim of the largest crater on Phobos, Stickney, has been perforated by an impact to reveal redder material and must therefore be relatively thin. A fresh impact with dark crater rays has been identified. Previously identified mass-wasting features in Stickney and Limtoc craters stand out strongly in colour. The interior deposits in Stickney appear more inhomogeneous than previously suspected. Several other local colour variations are also evident.Deimos is more uniform in colour but does show some small-scale inhomogeneity. The bright “streamers” (Thomas et al., Icarus, 123, 536–556,1996) are relatively blue. One crater to the south-west of Voltaire and its surroundings appear quite strongly reddened with respect to the rest of the surface. The reddening of the surroundings may be the result of ejecta from this impact.The spectral gradients at optical wavelengths observed for both Phobos and Deimos are quantitatively in good agreement with those found by unresolved photometric observations made by the Imager for Mars Pathfinder (IMP; Thomas et al., JGR, 104, 9055–9068, 1999). The spectral gradients of the blue and red units on Phobos bracket the results from IMP.  相似文献   

The Impact of Heterogeneities on the Evolution of Caprock Integrity Associated Only with Mineral Alterations Due to A Long-term CO2 Intrusion     

TIAN Hailong  Brian J. MCPHERSON  PAN Feng  XU Tianfu 《《地质学报》英文版》2013,87(Z1):963-963

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Convective mixing in formations with horizontal barriers     

《Advances in water resources》2013

It has been shown that convective mixing in porous media flow is important for applications such as saltwater intrusion and geological storage of carbon dioxide. In the latter case, dissolution from the injected phase to the resident brine is assisted by convective mixing, which leads to enhanced storage security through reduced buoyancy. Here, we focus on the effect of horizontal barriers on the efficiency of convective mixing. Previous investigations of the effect of heterogeneity on mixing efficiency have focused on random permeability fields or barriers of small extent compared to the intrinsic finger wavelength. The effect of horizontal barriers of larger extent, such as mudstone inclusions or thin shale deposits, has not been given sufficient attention. We perform detailed numerical investigations to represent the continuous solution of this problem in semi-infinite domains with barriers arranged in a periodic manner. The results show that mass flux into the domain, which is a measure of the efficiency of redistribution of the solute, is inversely proportional to the barrier length and proportional to the horizontal and vertical aperture between the barriers, for the cases studied. The flow structure is complex, and it depends not only on the total area of barriers but also largely on the distribution of barriers. Therefore, neither simple analytical models nor simple upscaling methods that lack information about the flow paths, can be used to predict the behavior. However, we compute the effective vertical permeability by flow-based upscaling and show that it can be used to directly obtain a first-order approximation to the mass flux into the domain.  相似文献   

新疆艾比湖周边白刺沙堆形态特征空间异质性研究   总被引：8，自引：1，他引：7  

刘金伟  李志忠  武胜利  李万娟  王少朴  曹向东  凌智永 《中国沙漠》2009,29(4):628-635

在实地调查和形态测量的基础上,应用统计学原理和方法,对新疆艾比湖周边白刺沙堆的实测形态参数进行数理统计分析,以分析艾比湖周边白刺沙堆的空间异质性。结果表明,艾比湖周边白刺沙堆的长轴平均长度介于4.5~7 m之间,短轴平均长度介于3~5.5 m之间,沙堆平均高度介于0.5~1 m之间;沙堆长轴、短轴、迎风坡坡长和背风坡坡长之间均具有显著相关性,尤其是长轴长度和背风坡坡长,短轴长度和迎风坡坡长具有高度相关性,沙堆的高度与短轴的相关程度最高。从白刺沙堆各发育阶段形态特征分析,艾比湖东部和东北部桑德库木和鸭子湾北部白刺沙堆处于生长阶段,艾比湖西部阿拉山口附近的白刺沙堆处于发育的衰退阶段。  相似文献