A locally conservative finite element framework for the simulation of coupled flow and reservoir geomechanics     

Birendra Jha  Ruben Juanes 《Acta Geotechnica》2007,2(3):139-153

In this paper, we present a computational framework for the simulation of coupled flow and reservoir geomechanics. The physical model is restricted to Biot’s theory of single-phase flow and linear poroelasticity, but is sufficiently general to be extended to multiphase flow problems and inelastic behavior. The distinctive technical aspects of our approach are: (1) the space discretization of the equations. The unknown variables are the pressure, the fluid velocity, and the rock displacements. We recognize that these variables are of very different nature, and need to be discretized differently. We propose a mixed finite element space discretization, which is stable, convergent, locally mass conservative, and employs a single computational grid. To ensure stability and robustness, we perform an implicit time integration of the fluid flow equations. (2) The strategies for the solution of the coupled system. We compare different solution strategies, including the fully coupled approach, the usual (conditionally stable) iteratively coupled approach, and a less common unconditionally stable sequential scheme. We show that the latter scheme corresponds to a modified block Jacobi method, which also enjoys improved convergence properties. This computational model has been implemented in an object-oriented reservoir simulator, whose modular design allows for further extensions and enhancements. We show several representative numerical simulations that illustrate the effectiveness of the approach.  相似文献   

Water residence time as a driving force of zooplankton structure and succession     

Ulrike Obertegger  Giovanna Flaim  Maria Giovanna Braioni  Ruben Sommaruga  Flavio Corradini  Andrea Borsato 《Aquatic Sciences - Research Across Boundaries》2007,69(4):575-583

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Causes and underlying processes of measurement variability in field erosion plots in Mediterranean conditions   总被引：1，自引：0，他引：1  

C. Boix‐Fayos  M. Martínez‐Mena  A. Calvo‐Cases  E. Arnau‐Rosalén  J. Albaladejo  V. Castillo 《地球表面变化过程与地形》2007,32(1):85-101

An understanding of the sources of variation in the use of erosion plots and of their feasibility to meet the objectives of each specific research project is key to improving future field designs, selecting data for modelling purposes and furthering knowledge of soil erosion processes. Our own field experiences from ongoing research on soil erosion processes since 1989, have allowed us to detect several methodological problems that cause measurement variability. Here several examples are presented concerning: (i) differences in long‐term soil erosion data between open and closed plots; (ii) differences in soil loss derived from replica soil erosion plots; and (iii) differences in soil loss data derived from plots at a range of spatial scales. Closed plots are not the most suitable method for long‐term monitoring of soil erosion rates due to the risk of exhaustion of available material within the plot. The difference in time after which exhaustion occurs depends on the surface soil characteristics, the climatological conditions and the size of the plots. We detected four and seven years as ‘time to exhaustion’. Different results are frequently obtained between pairs of replica plots. Differences up to a factor of nine have been detected in total soil loss between replica plots due to different spatial patterns of surface components. Different constraints appear depending on the spatial scale of measurement of soil loss. We obtained lower runoff percentages at coarser scales; however, larger sediment concentrations are observed at coarser scales (1·32 g l^?1, catchment; 0·30 g l^?1, 30 m²; 0·17 g l^?1, 1 m² scales). The smaller the plot, the larger the hydrological disconnection within the system, the lower the energy flows due to short distances and the quicker the response to runoff due to an artificial decrease of concentration times for continuous flow. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Water Quality Monitoring to Support the European Commission's Water Framework Directive Reporting Requirements     

José Antonio Álvarez-Robles  Miguel Ángel Latre  Pedro Rafael Muro-Medrano  Francisco Javier Zarazaga-Soria  Ruben Béjar 《Transactions in GIS》2007,11(6):835-847

This article aims at providing a simple way for water quality monitoring in a set of reservoirs using an earth observation‐based approach and the assessment of the use of this technique for a monitoring network in order to meet the requirements and objectives of the Water Framework Directive (WFD) by the Member States of the European Union. The study carried out was preformed in 42 reservoirs of the Ebro River Basin, in the northeast of Spain. The proposed methodology is based on the development of an algorithm for the estimation of water quality by means of LANDSAT TM band reflectance. Some band ratios were used in the model as well. Trophic State Index (TSI), calculated by means of Secchi Disc Transparency data, was estimated using a forward stepwise multiple regression analysis and the TM2 band and TM1/TM2 ratio. The final results showed a large variability in water quality across reservoirs. Moreover, substantial spatial heterogeneity was also observed in the water bodies. These results demonstrate the likelihood of developing a monitoring network based on remote sensing techniques for the implementation of the WFD.  相似文献   

Distribution and speciation of arsenic around roots in a contaminated riparian floodplain soil: Micro-XRF element mapping and EXAFS spectroscopy   总被引：4，自引：0，他引：4  

Andreas Voegelin  Frank-Andreas Weber  Ruben Kretzschmar 《Geochimica et cosmochimica acta》2007,71(23):5804-5820

Riparian soils are periodically flooded, leading to temporarily reducing conditions. Diffusion of O₂ through plants into the rhizosphere maintains oxic conditions around roots, thereby promoting trace element fractionation along a redox gradient from the reduced soil matrix towards the oxic rhizosphere. The aim of this study was to determine the distribution and speciation of arsenic around plant roots in a contaminated (170-280 mg/kg As) riparian floodplain soil (gleyic Fluvisol). The analysis of soil thin sections by synchrotron micro-X-ray fluorescence (μ-XRF) spectrometry showed that As and Fe were enriched around roots and that As was closely correlated with Fe. Arsenic contents of three manually separated rhizosphere soil samples from the subsoil were 5-9 times higher than respective bulk As contents. This corresponds to the accumulation of about half of the total As in the subsoil in Fe-enrichments around roots. The speciation of As in the soil was assessed by oxalate extractions at pH 3.0 as well as by X-ray absorption near edge structure (XANES) and extended X-ray fine structure (EXAFS) spectroscopy. More than 77% of the total As was oxalate extractable in all samples. XANES and EXAFS spectra demonstrated that As was predominantly As(V). For the accurate analysis of the EXAFS data with respect to the bonding of As(V) to the Fe- or Al-octahedra of (hydr)oxides and clays, all 3-leg and 4-leg multiple scattering paths within the As^(V)O₄-tetrahedron were considered in a fully constrained fitting scheme. We found that As(V) was predominantly associated with Fe-(hydr)oxides, and that sorption to Al- and Mn-hydroxides was negligible. The accumulation of As in the rhizosphere may affect As uptake by plants. Regarding the mobility of As, our results suggest that by oxygenation of the rhizosphere, plants attenuate the leaching of As from riparian floodplain soils during periods of high groundwater levels or flooding.  相似文献   

Establishing the ecological quality status of soft-bottom mining-impacted coastal water bodies in the scope of the Water Framework Directive     

Marín-Guirao L  Cesar A  Marín A  Lloret J  Vita R 《Marine pollution bulletin》2005,50(4):374-387

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Vertical distribution of suspended sediment concentrations seawards of the breaking zone     

Ruben D. Kos&#x;yan 《Coastal Engineering》1985,9(2):171-187

On the basis of the current concepts on the wave flow structure and solid particle motion in turbulent flow, an equation was derived which enables the suspended sediment concentration profile to be computed from known wave parameters. The equation was verified by laboratory and full-scale experiments which proved that it can be implemented for practical computations of the concentration profile seawards of the breaking zone. The formula yields the best results when operating on wave characteristics corresponding to maximum spectral density.  相似文献   

Lower Miocene gypsum palaeokarst in the Madrid Basin (central Spain): dissolution diagenesis, morphological relics and karst end-products     

Juan P. Rodríguez-Aranda  José P. Calvo  M. Esther Sanz-Montero 《Sedimentology》2002,49(6):1385-1400

Abstract The Miocene sedimentary record of the Madrid Basin displays several examples of palaeokarstic surfaces sculpted within evaporite formations. One of these palaeokarstic surfaces represents the boundary between two main lithostratigraphic units, the Miocene Lower and Intermediate units of the Madrid Basin. The palaeokarst formed in lacustrine gypsum deposits of Aragonian age and corresponds to a surface palaeokarst (epikarst), further buried by terrigenous deposits of the overlying unit. Karst features are recognized up to 5·5 m beneath the gypsum surface. Exokarst and endokarst zones are distinguished by the spatial distribution of solution features, i.e. karren, dolines, pits, conduits and caves, and collapse breccias, sedimentary fills and alteration of the original gypsum across the karst profiles. The development of the gypsum palaeokarst began after drying out of a saline lake basin, as supported by recognition of root tubes, later converted to cylindrical and funnel‐shaped pits, at the top of the karstic profiles. The existence of a shallow water table along with low hydraulic gradients was the main factor controlling the karst evolution, and explains the limited depth reached by both exokarst and endokarst features. Synsedimentary fill of the karst system by roughly laminated to massive clay mudstone with subordinate carbonate and clastic gypsum reflects a punctuated sedimentation regime probably related to episodic heavy rainfalls typical of arid to semi‐arid climates. Duration of karstification is of the order of several thousands of years, which is consistent with previous statements that gypsum karstification can develop rapidly over geologically short time periods.  相似文献   

Geotechnical engineering practice for collapsible soils   总被引：3，自引：0，他引：3  

Sandra L. Houston  William N. Houston  Claudia E. Zapata  Chris Lawrence 《Geotechnical and Geological Engineering》2001,19(3-4):333-355

Conditions in arid and semi-arid climates favor the formation of the most problematic collapsible soils. The mechanisms that account for almost all naturally occurring collapsible soil deposits are debris flows, rapid alluvial depositions, and wind-blown deposits (loess). Collapsible soils are moisture sensitive in that increase in moisture content is the primary triggering mechanism for the volume reduction of these soils. One result of urbanization in arid regions is an increase in soil moisture content. Therefore, the impact of development-induced changes in surface and groundwater regimes on the engineering performance of moisture sensitive arid soils, including collapsible soils, becomes a critical issue for continued sustainable population expansion into arid regions.In practicing collapsible soils engineering, geotechnical engineers are faced with (1) identification and characterization of collapsible soil sites, (2) estimation of the extent and degree of wetting, (3) estimation of collapse strains and collapse settlements, and (4) selection of design/mitigation alternatives. Estimation of the extent and degree of wetting is the most difficult of these tasks, followed by selection of the best mitigation alternative.  相似文献   

Unusual twinning features in large primary gypsum crystals formed in salt lake conditions, Middle Miocene, Madrid Basin, Spain: palaeoenvironmental implications—reply     

J. P. Rodríguez-Aranda  J. M. Rouchy  J. P. Calvo  S. Ordez  M. A. García del Cura 《Sedimentary Geology》1995,100(1-4)

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