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Renard, Philippe
Nom
Renard, Philippe
Affiliation principale
Fonction
Directeur de Recherche
Email
Philippe.Renard@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 10 sur 13
- PublicationAccès libreAnalog-based meandering channel simulation(2014-1-10)
; - PublicationAccès libreModeling Fine-Scale Geological Heterogeneity?Examples of Sand Lenses in Tills(2013-1-10)
; ; - PublicationAccès libre3D multiple-point statistics simulation using 2D training images(2012-3)
; One of the main issues in the application of multiple-point statistics (MPS) to the simulation of three-dimensional (3D) blocks is the lack of a suitable 3D training image. In this work, we compare three methods of overcoming this issue using information coming from bidimensional (20) training images. One approach is based on the aggregation of probabilities. The other approaches are novel. One relies on merging the lists obtained using the impala algorithm from diverse 2D training images, creating a list of compatible data events that is then used for the MPS simulation. The other (s2Dcd) is based on sequential simulations of 2D slices constrained by the conditioning data computed at the previous simulation steps. These three methods are tested on the reproduction of two 3D images that are used as references, and on a real case study where two training images of sedimentary structures are considered. The tests show that it is possible to obtain 3D MPS simulations with at least two 2D training images. The simulations obtained, in particular those obtained with the s2Dcd method, are close to the references, according to a number of comparison criteria. The CPU time required to simulate with the method s2Dcd is from two to four orders of magnitude smaller than the one required by a MPS simulation performed using a 3D training image, while the results obtained are comparable. This computational efficiency and the possibility of using MPS for 3D simulation without the need for a 3D training image facilitates the inclusion of MPS in Monte Carlo, uncertainty evaluation, and stochastic inverse problems frameworks. - PublicationAccès libreProbability Aggregation Methods in Geoscience(2012-1-10)
- PublicationAccès libreComparison of three geostatistical methods for hydrofacies simulation: a test on alluvial sediments(2012-1-10)
- PublicationAccès libreThree-dimensional high resolution fluvio-glacial aquifer analog - Part 2: Geostatistical modeling(2011-7-21)
; ; Bayer, PeterThe heterogeneity of sedimentary structures at the decimeter scale is crucial to the understanding of groundwater flow and transport. In a series of two papers, we provide a detailed analysis of a fluvio-glacial aquifer analog: the Herten site. The geological data along a series of 2D sections in a quarry, the corresponding GPR measurements, and their sedimentological interpretation are described in the companion paper. In this paper, we focus on the three-dimensional reconstruction of the heterogeneity. The resulting numerical model is provided as an electronic supplementary material for further studies. Furthermore, the geostatistical parameters derived from this analysis and the methodology described in the paper could be used in the future for the simulation of similar deposits where less data would be available. To build the 3D model, we propose a hierarchical simulation method which integrates various geostatistical techniques. First, we model the subdivision of the domain into regions corresponding to main sedimentological structures (e.g. a sedimentation event). Within these volumes, we use multiple-point statistics to describe the internal heterogeneity. What is unusual here is that we do not try to use a complex training image for the multiple-point algorithm accounting for all the non-stationarity and complexity, but instead use a simple conceptual model of heterogeneity (ellipsoidal shapes as a training image) and constrain the multiple point simulations within the regions by a detailed interpolation of orientation data derived from the 2D sections. This method produces realistic geological structures. The analysis of the flow and transport properties (hydraulic conductivity and tracer breakthrough curves) of the resulting model shows that it is closer to the properties estimated directly from the 2D geological observations rather than those estimated from a model of heterogeneity based on probability of transitions and not including the modeling of the large-scale structures. - PublicationAccès libreThree-dimensional high resolution fluvio-glacial aquifer analog - Part 1: Field study(2011)
; Comunian, AlessandroDescribing the complex structures that exist in many sedimentary aquifers is crucial for reliable groundwater flow and transport simulation. However, hardly any aquifer can be inspected in such detail that all decimeter to meter heterogeneity is resolved. Aquifer analogs serve as surrogates to construct models of equivalent heterogeneity, and thus imitate those features relevant for flow or transport processes. Gravel pits found in excavation show excellent sections of the sedimentary sequence and thus offer direct insight into the structural and textural composition of the subsoil. This paper describes an approach to also inspect the third dimension: by mapping during the ongoing excavation it is possible to obtain a three-dimensional representation of the subsurface within a short period of time. A detailed description of a case study is presented and the findings from sedimentological, hydrogeological and geophysical analyses are compared. The gravel pit is located near the town of Herten in southwest Germany, where relatively young unconsolidated fluvio-glacial and fluvial sediments in the Rhine basin are mined. The excavated gravel body is built up by architectural elements typical for braided river deposits. The study generated a high-resolution data set of lithofacies, hydrofacies and ground penetrating radar (GPR) profiles. It represents the basis for a full three-dimensional geostatistical reconstruction presented in the second part. - PublicationAccès libreProbability aggregaton methods and multiple-point statistics for 3D modeling of aquifer heterogeneity from 2D training images(2011)
; Multiple-point statistics (MPS) is a rising method for the characterization of heterogeneity. Its strength and its Achilles' heel lie in the training image, which is the conceptual model of geological heterogeneity on which MPS simulations are based. Indeed, on one side the use of the training image allows great flexibility when for example for bi-dimensional (2D) simulation a training image can be provided by a photo-mosaic of an outcrop or by a sketch drawn by a geologist. On the other side, in three-dimensions (3D) a training image is rarely available.
When the information provided by a 3D image is not accessible, then one must somehow use probabilistic information which comes from lower dimen- sion sources, like for example 2D training images. If different 2D sources of information are available, one possibility is to aggregate the corresponding probability information. This problem is very general and several methods exist. Two main categories of methods are distinguished: those based on the sum (convex) and those based on the multiplication (non-convex). When the weighting factors can be determined from some training data, the best reliabilities are obtained with the Beta-transformed linear pool and the Bor- diey's formula. Instead, when training data are not accessible, reasonably reliable results can be obtained with the Bordley's formula and with the Markovian-type categorical prediction.
One convex method and one non-convex method are tested for the ag- gregation of information coming from 2D training images. For the tests, one 3D image of a micro-computed tomography of a sandstone and one 3D realization of a fluvio-glacial environment are used as references. Two di- mensional slices of the reference 3D images are used as training images for providing the information to be aggregated with the methods cited above, but also for the simulation with two novel method proposed here. One of this methods is baaed on sequential 2D simulations conditioned by the data computed during the previous simulation steps (method s2Dcd). With this last method it is possible to obtain , without the use of a 3D training im- age, 3D simulations which can be considered close to the reference images according to most comparison criteria considered. Moreover, while the re- sults obtained with the method s2Dcd are close to the results obtained with a MPS simulation which make use of a 3D training image, the CPU time required by s2Dcd is from two to four orders of magnitude smaller than with a traditional 3D simulation. This computational efficiency is a step forward for the introduction of MPS in frameworks which require a great number of realizations in a reasonably restricted amount of time, like for example Monte Carlo methods or stochastic inverse problems.
Other techniques exists to deal with the simulation in 3D when a 3D training image is not available. One of this techniques, developed in this thesis' framework, is applied for the simulation of the image of the fluvio- glacial aquifer analog used as reference for the tests depicted above. It is a hierarchical technique: six parallel outcrops mapped during a quarry excava- tion serve to recognize geological features at different scales and on different depositional layers. Once the complexity of the observed heterogeneity is simplified, object based techniques are used to simulate 3D training images containing simple shapes. Maps of the orientation of the main geological structures are created by interpolating orientations derived from morpholog- ical analysis. All these information are then included in a MPS simulation framework. The geological heterogeneity reproduced using this technique is realistic and can provide an high-resolution benchmark for fluid flow and transport problems.
In summary, this thesis demonstrates that is is possible to apply MPS methods obtaining credible results from a geological point of view even in absence of a 3D training image. - PublicationAccès libreIntroducing wwhypda: a world-wide collaborative hydrogeological parameters database(2009-1-10)
- PublicationAccès libreIntroducing wwhypda : a world-wide collaborative hydrogeological parameters database(2009)