共查询到20条相似文献，搜索用时 593 毫秒
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According to the ecosystem assessment framework developed by the Millennium Ecosystem Assessment (MA), this paper designs
an evaluation system of ecosystem services in Poyang Lake area. On the basis of relevant variables disaggregated to 1 km grid
using the gridded 1 km, this paper employs factor analysis to extract a number of factors which characterize the ecosystem
services of Poyang Lake area. The extracted principal component are then represented onto 1 km×1 km grids by spatial clustering
analysis to recognize and identify the minimal but consistent mapping units for ecosystem services which can be used to delimit
the boundaries of ecological service zones. The research identifies ten ecosystem service zones in Poyang Lake area according
to the consistent principle of core ecosystem service unit. Four kinds of core ecosystem services including supporting function,
provisioning function, regulating function and cultural function are identified and represented. The research results could
provide both spatially and temporally valuable decision-making information for sustainable ecosystem management in the targeted
area. 相似文献
3.
This paper proposes a systematic framework for real-time assessment of spatial liquefaction hazard of port areas considering local seismic response characteristics based on a geographic information system (GIS) platform. The framework is integrated and embedded with sequential, interrelated subprocedures and a database for liquefaction-induced damage evaluation that standardizes and both individually and collectively quantifies analytical results. To integrate the current in situ condition of a selected port area, the framework functions as a spatial database system for geotechnical and structural data and as a recipient of automatic transmission of seismic monitoring data. The geotechnical profile correlated with liquefaction potential is compiled into a geotechnical spatial grid built by geostatistical methods. Linked with the geotechnical spatial grid, the processing of site-specific responses is automatically interpreted from previously derived correlations between rock acceleration and maximum acceleration of each soil layer. As a result, the liquefaction severity is determined based on a combined geotechnical spatial grid with seismic load correlation in real-time according to a simplified procedure, allowing calculation of the liquefaction potential index (LPI). To demonstrate practical applications of the framework in estimating the liquefaction hazard in real-time, liquefaction-hazard maps were visualized for two earthquake scenarios, verifying the applicability of the proposed framework. 相似文献
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Gang Yao Nuno Vieira da Silva Henry Alexander Debens Di Wu 《Computational Geosciences》2018,22(2):469-484
Finite difference is the most widely used method for seismic wavefield modeling. However, most finite-difference implementations discretize the Earth model over a fixed grid interval. This can lead to irregular model geometries being represented by ‘staircase’ discretization, and potentially causes mispositioning of interfaces within the media. This misrepresentation is a major disadvantage to finite difference methods, especially if there exist strong and sharp contrasts in the physical properties along an interface. The discretization of undulated seabed bathymetry is a common example of such misrepresentation of the physical properties in finite-difference grids, as the seabed is often a particularly sharp interface owing to the rapid and considerable change in material properties between fluid seawater and solid rock. There are two issues typically involved with seabed modeling using finite difference methods: firstly, the travel times of reflections from the seabed are inaccurate as a consequence of its spatial mispositioning; secondly, artificial diffractions are generated by the staircase representation of dipping seabed bathymetry. In this paper, we propose a new method that provides a solution to these two issues by positioning sharp interfaces at fractional grid locations. To achieve this, the velocity model is first sampled in a model grid that allows the center of the seabed to be positioned at grid points, before being interpolated vertically onto a regular modeling grid using the windowed sinc function. This procedure allows undulated seabed bathymetry to be represented with improved accuracy during modeling. Numerical tests demonstrate that this method generates reflections with accurate travel times and effectively suppresses artificial diffractions. 相似文献
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Stochastic Structural Modeling 总被引：3，自引：0，他引：3
Lars Holden Petter Mostad Bjørn Fredrik Nielsen Jon Gjerde Chris Townsend Signe Ottesen 《Mathematical Geology》2003,35(8):899-914
A consistent stochastic model for faults and horizons is described. The faults are represented as a parametric invertible deformation operator. The faults may truncate each other. The horizons are modeled as correlated Gaussian fields and are represented in a grid. Petrophysical variables may be modeled in a reservoir before faulting in order to describe the juxtaposition effect of the faulting. It is possible to condition the realization on petrophysics, horizons, and fault plane observations in wells in addition to seismic data. The transmissibility in the fault plane may also be included in the model. Four different methods to integrate the fault and horizon models in a common model is described. The method is illustrated on an example from a real petroleum field with 18 interpreted faults that are handled stochastically. 相似文献
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Eirik Keilegavlen Jeremy E. Kozdon Bradley T. Mallison 《Computational Geosciences》2012,16(4):1021-1042
The governing equations for multiphase flow in porous media have a mixed character, with both nearly elliptic and nearly hyperbolic variables. The flux for each phase can be decomposed into two parts: (1) a geometry- and rock-dependent term that resembles a single-phase flux; and (2) a mobility term representing fluid properties and rock–fluid interactions. The first term is commonly discretized by two- or multipoint flux approximations (TPFA and MPFA, respectively). The mobility is usually treated with single-point upstream weighting (SPU), also known as dimensional or donor cell upstream weighting. It is well known that when simulating processes with adverse mobility ratios, SPU suffers from grid orientation effects. An important example of this, which will be considered in this work, is the displacement of a heavy oil by water. For these adverse mobility ratio flows, the governing equations are unstable at the modeling scale, rendering a challenging numerical problem. These challenges must be addressed in order to avoid systematic biasing of simulation results. In this work, we present a framework for multidimensional upstream weighting for multiphase flow with buoyancy on general two-dimensional grids. The methodology is based on a dual grid, and the resulting transport methods are provably monotone. The multidimensional transport methods are coupled with MPFA methods to solve the pressure equation. Both explicit and fully implicit approaches are considered for time integration of the transport equations. The results show considerable reduction of grid orientation effects compared to SPU, and the explicit multidimensional approach allows larger time steps. For the implicit method, the total number of non-linear iterations is also reduced when multidimensional upstream weighting is used. 相似文献
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Jeremy Edward Kozdon Bradley T. Mallison Margot G. Gerritsen 《Computational Geosciences》2011,15(3):399-419
Truly multidimensional methods for hyperbolic equations use flow-based information to determine the computational stencil,
as opposed to applying one-dimensional methods dimension by dimension. By doing this, the numerical errors are less correlated
with the underlying computational grid. This can be important for reducing bias in flow problems that are inherently unstable
at simulation scale, such as in certain porous media problems. In this work, a monotone, multi-D framework for multiphase
flow and transport in porous media is developed. A local coupling of the fluxes is introduced through the use of interaction
regions, resulting in a compact stencil. A relaxed volume formulation of the coupled hyperbolic–elliptic system is used that
allows for nonzero residuals in the pressure equation to be handled robustly. This formulation ensures nonnegative masses
and saturations (volume fractions) that sum to one (Acs et al., SPE J 25(4):543–553, 1985). Though the focus of the paper is on immiscible flow, an extension of the methods to a class of more general scalar hyperbolic
equations is also presented. Several test problems demonstrate that the truly multi-D schemes reduce biasing due to the computational
grid. 相似文献
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Knut–Andreas Lie Stein Krogstad Ingeborg Skjelkv?le Ligaarden Jostein Roald Natvig Halvor M?ll Nilsen B?rd Skaflestad 《Computational Geosciences》2012,16(2):297-322
Accurate geological modelling of features such as faults, fractures or erosion requires grids that are flexible with respect
to geometry. Such grids generally contain polyhedral cells and complex grid-cell connectivities. The grid representation for
polyhedral grids in turn affects the efficient implementation of numerical methods for subsurface flow simulations. It is
well known that conventional two-point flux-approximation methods are only consistent for K-orthogonal grids and will, therefore, not converge in the general case. In recent years, there has been significant research
into consistent and convergent methods, including mixed, multipoint and mimetic discretisation methods. Likewise, the so-called
multiscale methods based upon hierarchically coarsened grids have received a lot of attention. The paper does not propose
novel mathematical methods but instead presents an open-source Matlab? toolkit that can be used as an efficient test platform for (new) discretisation and solution methods in reservoir simulation.
The aim of the toolkit is to support reproducible research and simplify the development, verification and validation and testing
and comparison of new discretisation and solution methods on general unstructured grids, including in particular corner point
and 2.5D PEBI grids. The toolkit consists of a set of data structures and routines for creating, manipulating and visualising
petrophysical data, fluid models and (unstructured) grids, including support for industry standard input formats, as well
as routines for computing single and multiphase (incompressible) flow. We review key features of the toolkit and discuss a
generic mimetic formulation that includes many known discretisation methods, including both the standard two-point method
as well as consistent and convergent multipoint and mimetic methods. Apart from the core routines and data structures, the
toolkit contains add-on modules that implement more advanced solvers and functionality. Herein, we show examples of multiscale
methods and adjoint methods for use in optimisation of rates and placement of wells. 相似文献
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Linda Werner Hartman 《Mathematical Geology》2006,38(2):113-133
Spatial datasets are common in the environmental sciences. In this study we suggest a hierarchical model for a spatial stochastic field. The main focus of this article is to approximate a stochastic field with a Gaussian Markov Random Field (GMRF) to exploit computational advantages of the Markov field, concerning predictions, etc. The variation of the stochastic field is modelled as a linear trend plus microvariation in the form of a GMRF defined on a lattice. To estimate model parameters we adopt a Bayesian perspective, and use Monte Carlo integration with samples from Markov Chain simulations. Our methods does not demand lattice, or near-lattice data, but are developed for a general spatial data-set, leaving the lattice to be specified by the modeller. The model selection problem that comes with the artificial grid is in this article addressed with cross-validation, but we also suggest other alternatives. From the application of the methods to a data set of elemental composition of forest soil, we obtained predictive distributions at arbitrary locations as well as estimates of model parameters. 相似文献
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Trond Mannseth 《Computational Geosciences》2007,11(1):59-72
We consider discretization on quadrilateral grids of an elliptic operator occurring, for example, in the pressure equation
for porous-media flow. In a realistic setting – with non-orthogonal grid, and anisotropic, heterogeneous permeability – special
discretization techniques are required. Mixed finite element (MFE) and multipoint flux approximation (MPFA) are two methods
that can handle such situations. Previously, a framework for analytical comparison of MFE and MPFA in special cases has been
suggested. A comparison of MFE and MPFA-O (one of two main variants of MPFA) for isotropic, homogeneous permeability on a
uniformly distorted grid was also performed. In the current paper, we utilize the suggested framework in a slightly different
manner to analyze and compare MFE, MPFA-O and MPFA-U (the second main variant of MPFA). We reconsider the case previously
analyzed. We also consider the case of generally anisotropic, homogeneous permeability on an orthogonal grid. 相似文献
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提出了森林茂密,松散覆盖层较厚地区的遥感基础图象制作方法,利用热红外波段及生物地球化学遥感技术地植被覆盖区与金有关异常信息的提取;建立了植被覆盖区遥感构造解译标志,解译出４组线性构造,百余个环形构造和一个大型环块构造;将区域构造应力场的演化划分为３个阶段,ＮＥ－ＮＮＥ与ＮＷ,近ＥＷ向构造带相互交织成菱形格子状构造是本区构造的基本格架;大型环块构造及其周边环形构造和菱格状构造的各“角”区,往往是金矿 相似文献
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Bacteria and dissolved humic substances are capable of binding significant concentrations of metals in natural environments. Recent advances in understanding bacteria-metal and humic-metal complexation have provided a framework for directly comparing the binding capacities of these components. In this study, we use chemical equilibrium modeling to construct an internally consistent set of thermodynamic equilibrium constants for proton and Cd binding onto dissolved humic substances, using a variety of published data sets. Our modeling approach allows for the direct comparison of humic substance binding constants and site densities to those previously published for proton and Cd binding onto natural consortia of bacteria. We then combine these constants into a unified model that accounts for the competition between bacterial surfaces and humic and fulvic acids in order to determine the relative importance of each component on the total Cd budget. The combined model is used to examine the relative contributions of bacteria and dissolved humic substances to Cd complexation in natural settings. Calculations are performed for three representative systems: (1) one with a maximum realistic concentration of bacteria and a minimum realistic concentration of humic substance, (2) one with a maximum realistic concentration of humic substance and a minimum concentration of bacteria, and (3) one with an intermediate concentration of both components.Our modeling results indicate that dissolved humic substances have 2 orders of magnitude more available binding sites than bacterial surfaces (per gram). Humic substances also have a greater affinity than bacterial surfaces for binding Cd over circumneutral pH ranges. The combined model results demonstrate that, depending upon their relative concentrations, both Cd-humic and Cd-bacteria complexes are capable of dominating Cd-speciation in specific natural environments. This modeling approach is useful in that it can easily be extended to include other metals and binding ligands; however, thermodynamic data must be gathered on additional components to facilitate the modeling of more realistic systems. 相似文献
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网格单元法和地质体单元法是目前运用在矿产预测中最普遍的地质统计方法,2种方法各有优缺点。为了更好地使2种方法扬长避短,以青海省祁漫塔格地区接触交代型铁铜矿床为例,在其找矿预测模型的背景下,运用网格法和地质体法分别进行资源预测;并在运用地质体单元法时,在传统的圈定地质体界限的同时,也对地质体本身进行了网格划分,从而进一步进行证据权的计算,得到后验概率值。2种方法得到的结果较一致,证明新地质体法的可靠性。将预测结果结合地质体分级情况、地质体法和网格法阈值大小综合考虑,圈定出预测远景区,从而划定靶区。预测出的靶区既是找矿后验概率的高值区域,又是成矿最有利的地质体区域。 相似文献
15.
Conditional Simulation with Patterns 总被引：17，自引：0，他引：17
An entirely new approach to stochastic simulation is proposed through the direct simulation of patterns. Unlike pixel-based
(single grid cells) or object-based stochastic simulation, pattern-based simulation simulates by pasting patterns directly
onto the simulation grid. A pattern is a multi-pixel configuration identifying a meaningful entity (a puzzle piece) of the
underlying spatial continuity. The methodology relies on the use of a training image from which the pattern set (database)
is extracted. The use of training images is not new. The concept of a training image is extensively used in simulating Markov
random fields or for sequentially simulating structures using multiple-point statistics. Both these approaches rely on extracting
statistics from the training image, then reproducing these statistics in multiple stochastic realizations, at the same time
conditioning to any available data. The proposed approach does not rely, explicitly, on either a statistical or probabilistic
methodology. Instead, a sequential simulation method is proposed that borrows heavily from the pattern recognition literature
and simulates by pasting at each visited location along a random path a pattern that is compatible with the available local
data and any previously simulated patterns. This paper discusses the various implementation details to accomplish this idea.
Several 2D illustrative as well as realistic and complex 3D examples are presented to showcase the versatility of the proposed
algorithm. 相似文献
16.
I. Lerche 《Mathematical Geology》1991,23(1):137-155
Several different proposed models of thermocatalytic cracking of kerogen to hydrocarbons are exhibited. The specific models are then combined into a single generic, encompassing framework. For laboratory pyrolysis measurements of kerogen degradation and of thermal generation of hydrocarbons, inverse methods are used to show how to determine the relevant distributions of kinetic parameters consistent with the measured data. 相似文献
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Multiscale methods can in many cases be viewed as special types of domain decomposition preconditioners. The localisation
approximations introduced within the multiscale framework are dependent upon both the heterogeneity of the reservoir and the
structure of the computational grid. While previous works on multiscale control volume methods have focused on heterogeneous
elliptic problems on regular Cartesian grids, we have tested the multiscale control volume formulations on two-dimensional
elliptic problems involving heterogeneous media and irregular grid structures. Our study shows that the tangential flow approximation
commonly used within multiscale methods is not suited for problems involving rough grids. We present a more robust mass conservative
domain decomposition preconditioner for simulating flow in heterogeneous porous media on general grids. 相似文献
19.
While 3D seismic has been the basis for geological model building for a long time, time-lapse seismic has primarily been used
in a qualitative manner to assist in monitoring reservoir behavior. With the growing acceptance of assisted history matching
methods has come an equally rising interest in incorporating 3D or time-lapse seismic data into the history matching process
in a more quantitative manner. The common approach in recent studies has been to invert the seismic data to elastic or to
dynamic reservoir properties, typically acoustic impedance or saturation changes. Here we consider the use of both 3D and
time-lapse seismic amplitude data based on a forward modeling approach that does not require any inversion in the traditional
sense. Advantages of such an approach may be better estimation and treatment of model and measurement errors, the combination
of two inversion steps into one by removing the explicit inversion to state space variables, and more consistent dependence
on the validity of assumptions underlying the inversion process. In this paper, we introduce this approach with the use of
an assisted history matching method in mind. Two ensemble-based methods, the ensemble Kalman filter and the ensemble randomized
maximum likelihood method, are used to investigate issues arising from the use of seismic amplitude data, and possible solutions
are presented. Experiments with a 3D synthetic reservoir model show that additional information on the distribution of reservoir
fluids, and on rock properties such as porosity and permeability, can be extracted from the seismic data. The role for localization
and iterative methods are discussed in detail. 相似文献
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作为深时数字地球项目的底层框架,全球古地理重建模型包括地质历史时期板块的位置和运动轨迹以及地表特征两方面的内容。过去数十年里,基于不同方法、不同资料的全球古地理重建模型不断涌现。综合古地磁学、古生物学、沉积学、地球物理、地球化学以及地球动力学领域的知识与资料解释古地理,并建立起数字化、可修改、随时间演变的模型是当前常见的方法。文章介绍了国内外全球古地理重建模型的构建方法,并比较了六种主流的重建模型(PaleoMap、PLATES、UNIL、GOLONKA、GMAP和EarthByte),旨在为国内相关领域研究提供参考。文章还介绍了数字化全球重建古地理模型在古气候、板块构造驱动力以及盆地演化方面的应用及知识发现。通过对现存模型的介绍,提出展望,希望在深时数字地球计划的框架下整合国内外优秀科学家,重新设计并建立真正统一的四维古地理重建模型。 相似文献