Discrete fracture model for simulating waterflooding processes under fracturing conditions          下载免费PDF全文

Emil Gallyamov  Timur Garipov  Denis Voskov  Paul Van den Hoek 《国际地质力学数值与分析法杂志》2018,42(13):1445-1470

In our study, we develop a model for simulating fracturing processes in a poroelastic medium. The proposed approach combines the discrete fracture model enriched with contact plane mechanics. The model captures mechanical interactions of fractures and a deformable medium, fluid, and heat transfer in fractures and in a porous medium. Both effects of poroelasticity and thermoelasticity are accounted in our model. Mass and heat conservation equations are approximated by the finite volume method, and mechanical equilibrium equations are discretized by means of the Galerkin finite element approach. Two‐dimensional grid facets between 3‐dimensional finite elements are considered as possible fracture surfaces. Most of these facets are inactive from the beginning and are activated throughout the simulation. A fracture propagation criterion, based on Irwin's approach, is verified on each nonlinear iteration. When the criterion is satisfied, additional contact elements are added into finite element and discrete fracture model formulations respectively. The proposed approach allows modeling of existing natural and artificially created fractures within one framework. The model is tested on single‐ and multiple‐phase fluid flow examples for both isothermal and thermal conditions and verified against existing semianalytical solutions. The applicability of the approach is demonstrated on an example of practical interests where a sector model of an oil reservoir is simulated with different injection and production regimes.  相似文献   

River flooding and landscape changes impact ecological conditions of a scour hole lake in the Rhine-Meuse delta,The Netherlands     

H. Cremer  F. P. M. Bunnik  T. H. Donders  W. Z. Hoek  M. Koolen-Eekhout  H. H. Koolmees  E. Lavooi 《Journal of Paleolimnology》2010,44(3):789-801

A 400-year sediment record from an 18 m deep scour hole lake (Haarsteegse Wiel) near the Meuse River in the Netherlands was investigated for past changes in water quality, flooding frequency and landscape change using geophysical, geochemical and micropaleontological information. The results are highly significant for determining long-term trends of water quality, the impact of atmospheric (as SCP, spheroidal carbonaceous particles) and industrial (chromium) pollution on the terrestrial and aquatic flora, and the impact of river floods. The studied sediment record was dated by combining ¹³⁷Cs activities, biostratigraphical ages, micro-tephra layers, and historically documented floods indicated by the magnetic susceptibility. The oldest flooding event is indicated at AD 1610 when the lake was created by water masses bursting through a dike. Large historical river floods are well documented in regional chronicles and thus may provide reliable age calibration points. Based on assumptions about the timing of flood events and constant rate of sedimentation, it appears that sedimentation rates in Haarsteegse Wiel declined after ca. AD 1880. This decline might be a result of a widespread change from wheat cultivation to pasture land from around AD 1875 as a direct result of falling wheat prices and intensified cattle farming linked to the agricultural crisis in the last quarter of the nineteenth century. Water quality changes and absolute phosphorus concentrations were reconstructed using a diatom-based transfer function. Results show that the currently nutrient-rich lake has mostly been in a mesotrophic state prior to ca. AD 1920, with the exception of several apparently sharp eutrophication events that were coeval with river floods. River flooding also impacted the vegetation composition by importing allochthonous components, and indirectly by the influx of nutrients which had a clear influence on the composition of the water plant communities and aquatic species diversity. Magnetic susceptibility changes and pollen data show that within the period AD 1610–1740, within the Little Ice Age period, several undocumented floods may have occurred. Thus, documentation of geophysical, geochemical, and biological flooding signals in a high-resolution archive present the possibility to detect flooding regimes further back in time.  相似文献   

Symbiont-specific responses in foraminifera to the herbicide diuron     

van Dam JW  Negri AP  Mueller JF  Uthicke S 《Marine pollution bulletin》2012,65(4-9):373-383

The effects of the photosystem II (PSII) herbicide diuron was assessed on thirteen tropical foraminifera hosting diatom, dinoflagellate, red or green algae endosymbionts. Inhibition of photosynthesis (reduced ΔF/F(m)(')) by diuron depended on both symbiont type and test ultrastructure, with greatest sensitivity observed for diatom- and chlorophyte-hosting species (24h IC(25) 2.5-4μg L(-1)). Inhibition kinetics was slow (24-48h until maximum inhibition) in comparison with corals, suggesting structural differences may influence herbicide uptake and transport. Although foraminifera were generally less sensitive to direct effects of diuron (inhibition ΔF/F(m)(')) than other marine phototrophs, damage to PSII (reduction F(v)/F(m)) occurred at concentrations lower than observed for other organisms (24h IC(25) 3-12μg L(-1)). Damage to PSII was highly light dependent and occurred at very low light intensities indicating limited photoprotective capacity. The high diversity, widespread occurrence and relative sensitivity make foraminifera good bioindicator organisms to evaluate phytotoxic stress on coral reefs.  相似文献   

Unified multi‐depth‐level field decomposition          下载免费PDF全文

Niels Grobbe  Joost van der Neut  Evert Slob  Kees Wapenaar  Carlos Almagro Vidal  Guy Drijkoningen 《Geophysical Prospecting》2016,64(2):361-391

Wavefield decomposition forms an important ingredient of various geophysical methods. An example of wavefield decomposition is the decomposition into upgoing and downgoing wavefields and simultaneous decomposition into different wave/field types. The multi‐component field decomposition scheme makes use of the recordings of different field quantities (such as particle velocity and pressure). In practice, different recordings can be obscured by different sensor characteristics, requiring calibration with an unknown calibration factor. Not all field quantities required for multi‐component field decomposition might be available, or they can suffer from different noise levels. The multi‐depth‐level decomposition approach makes use of field quantities recorded at multiple depth levels, e.g., two horizontal boreholes closely separated from each other, a combination of a single receiver array combined with free‐surface boundary conditions, or acquisition geometries with a high‐density of vertical boreholes. We theoretically describe the multi‐depth‐level decomposition approach in a unified form, showing that it can be applied to different kinds of fields in dissipative, inhomogeneous, anisotropic media, e.g., acoustic, electromagnetic, elastodynamic, poroelastic, and seismoelectric fields. We express the one‐way fields at one depth level in terms of the observed fields at multiple depth levels, using extrapolation operators that are dependent on the medium parameters between the two depth levels. Lateral invariance at the depth level of decomposition allows us to carry out the multi‐depth‐level decomposition in the horizontal wavenumber–frequency domain. We illustrate the multi‐depth‐level decomposition scheme using two synthetic elastodynamic examples. The first example uses particle velocity recordings at two depth levels, whereas the second example combines recordings at one depth level with the Dirichlet free‐surface boundary condition of zero traction. Comparison with multi‐component decomposed fields shows a perfect match in both amplitude and phase for both cases. The multi‐depth‐level decomposition scheme is fully customizable to the desired acquisition geometry. The decomposition problem is in principle an inverse problem. Notches may occur at certain frequencies, causing the multi‐depth‐level composition matrix to become uninvertible, requiring additional notch filters. We can add multi‐depth‐level free‐surface boundary conditions as extra equations to the multi‐component composition matrix, thereby overdetermining this inverse problem. The combined multi‐component–multi‐depth‐level decomposition on a land data set clearly shows improvements in the decomposition results, compared with the performance of the multi‐component decomposition scheme.  相似文献   

Overcoming Squeezing in the Yacambú-Quibor Tunnel,Venezuela   总被引：2，自引：2，他引：0  

E. Hoek  R. Guevara 《Rock Mechanics and Rock Engineering》2009,42(2):389-418

Summary  The 5 m diameter 23.3 km long Yacambú-Quibor tunnel is designed to carry water through the Andes from the Yacambú dam in the wet tropical Orinoco basin to the semi-arid but fertile Quibor basin in western Venezuela. The tunnel is excavated in silicified and graphitic phyllites at depths of up to 1270 m below surface and extreme squeezing problems have been encountered. Construction involved 8 contracts extending over 32 years with breakthrough being achieved in July 2008. Several excavation methods and various lining designs were used over the years until the adoption of yielding support permitted the Owner and the Contractor to agree that only a circular section would be used and emphasis was placed on developing a routine construction procedure, irrespective of the rock conditions encountered at the face. This paper describes some of the rock engineering issues that were faced during the construction of this tunnel. Correspondence: E. Hoek, Consulting Engineer, Vancouver, Canada  相似文献   

基于岩土材料层析成像的孔隙网络构建算法     

任显卓  LINDEN Joost van der  NARSILIO Guillermo 《现代地质》2019,33(2):345-356

孔隙网络模型是研究多孔介质和其中颗粒的关键。现有的构建孔隙网络模型的算法有许多,但人们开始越来越多地研究基于图像的算法。将讨论一种基于中轴线的孔隙网络构建算法,并且对原有算法中孔隙中心表示方法不合理及缺少中轴线上各点坐标的问题提出改进,改进后的算法提出了孔隙中心的另一种表示方法,并且中轴线上任一点的坐标都被标出。在构建孔隙网络模型后利用该模型计算孔隙体积和喉径,并且针对过度分割的问题提出基于欧氏距离及基于分水岭算法的两种融合算法对孔隙和孔喉进行融合。  相似文献   

Accuracy and precision of the cosmic-ray neutron sensor for soil moisture estimation at humid environments     

Joost Iwema  Martin Schrön  Juliana Koltermann Da Silva  Rodolfo Schweiser De Paiva Lopes  Rafael Rosolem 《水文研究》2021,35(11):e14419

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Seismic reflection coefficients of faults at low frequencies: a model study     

Joost van der Neut  Mrinal K. Sen  Kees Wapenaar 《Geophysical Prospecting》2008,56(3):287-292

We use linear slip theory to evaluate seismic reflections at non‐welded interfaces, such as faults or fractures, sandwiched between general anisotropic media and show that at low frequencies the real parts of the reflection coefficients can be approximated by the responses of equivalent welded interfaces, whereas the imaginary parts can be related directly to the interface compliances. The imaginary parts of low frequency seismic reflection coefficients at fault zones can be used to estimate the interface compliances, which can be related to fault properties upon using a fault model. At normal incidence the expressions uncouple and the complex‐valued P‐wave reflection coefficient can be related linearly to the normal compliance. As the normal compliance is highly sensitive to the infill of the interface, it can be used for gas/fluid identification in the fault plane. Alternatively, the tangential compliance of a fault can be estimated from the complex‐valued S‐wave reflection coefficient. The tangential compliance can provide information on the crack density in a fault zone. Coupling compliances can be identified and quantified by the observation of PS conversion at normal incidence, with a comparable linear relationship.  相似文献   

Review paper: Virtual sources and their responses,Part II: data‐driven single‐sided focusing          下载免费PDF全文

Kees Wapenaar  Jan Thorbecke  Joost van der Neut  Evert Slob  Roel Snieder 《Geophysical Prospecting》2017,65(6):1430-1451

In Part I of this paper, we defined a focusing wave field as the time reversal of an observed point‐source response. We showed that emitting a time‐reversed field from a closed boundary yields a focal spot that acts as an isotropic virtual source. However, when emitting the field from an open boundary, the virtual source is highly directional and significant artefacts occur related to multiple scattering. The aim of this paper is to discuss a focusing wave field, which, when emitted into the medium from an open boundary, yields an isotropic virtual source and does not give rise to artefacts. We start the discussion from a horizontally layered medium and introduce the single‐sided focusing wave field in an intuitive way as an inverse filter. Next, we discuss single‐sided focusing in two‐dimensional and three‐dimensional inhomogeneous media and support the discussion with mathematical derivations. The focusing functions needed for single‐sided focusing can be retrieved from the single‐sided reflection response and an estimate of the direct arrivals between the focal point and the accessible boundary. The focal spot, obtained with this single‐sided data‐driven focusing method, acts as an isotropic virtual source, similar to that obtained by emitting a time‐reversed point‐source response from a closed boundary.  相似文献   

Risk-based input�Coutput analysis of hurricane impacts on interdependent regional workforce systems     

Rehman Akhtar  Joost R. Santos 《Natural Hazards》2013,65(1):391-405

Natural disasters, like hurricanes, can damage properties and critical infrastructure systems, degrade economic productivity, and in extreme situations can cause injuries and mortalities. This paper focuses particularly on workforce disruptions in the aftermath of hurricanes. We extend the dynamic inoperability input?Coutput model (DIIM) by formulating a workforce recovery model to identify critical industry sectors. A decision analysis tool is utilized by integrating the economic loss and inoperability metrics to study the interdependent effects of various hurricane intensities on Virginia??s workforce sectors. The extended DIIM and available workforce survey data are incorporated in the decision support tool to simulate various hurricane scenarios. For a low-intensity hurricane scenario, the simulated total economic loss to Virginia??s industry sectors due to workforce absenteeism is around $410 million. Examples of critical sectors that suffer the highest losses for this scenario include: (1) miscellaneous professional, scientific, and technical services; (2) federal general government; (3) state and local government enterprises; (4) construction; and (5) administrative and support services. This paper also explores the inoperability metric, which describes the proportion in which a sector capacity is disrupted. The inoperability metric reveals a different ranking of critical sectors, such as: (1) social assistance; (2) hospitals and nursing and residential care facilities; (3) educational services; (4) federal government enterprises; and (5) federal general government. Results of the study will help identify the critical workforce sectors and can ultimately provide insights into formulating preparedness decisions to expedite disaster recovery. The model was applied to the state of Virginia but can be generalized to other regions and other disaster scenarios.  相似文献