共查询到10条相似文献，搜索用时 234 毫秒
1.
Thomas H. Robey 《Mathematical Geology》1995,27(6):709-729
Geostatistical techniques allow simulation of properties such as porosity or conductivity on a fine scale. Typically, porous media flow modeling is performed at a coarser scale. Upscaling properties from the fine scale to the coarser scale introduces potential errors which are constrained by the degree of homogeneity of the cell or element. Adaptive grid techniques can be used to minimize the heterogeneity in the individual cells or elements, thus minimizing potential upscaling errors. A geostatistical adaptive grid (GAG) algorithm based on local minimization of heterogeneity is introduced. Local minimization allows greater control over the type of distortion permitted. Comparisons are made with a general elastic grid adjustment (GEGA) algorithm based on global minimization of heterogeneity. Several sample problems are used to test and demonstrate the two approaches. 相似文献
2.
Numerical simulation is an essential component of many studies of geological storage of carbon dioxide, but care must be taken to ensure the accuracy of the results. Unlike several other possible sources of simulation errors, which have previously been considered in detail and have well-understood techniques for mitigating their effects, comparatively little discussion of the spatial grid dependence of the dissolution rate of carbon dioxide into the formation water has appeared in the literature, despite its importance to simulation studies of geological storage of carbon dioxide in saline aquifers. In many instances, sufficient refinement of the computational grid can be a practical solution. However, this approach is not always feasible, especially for large-scale simulations in three dimensions requiring multiple realisations, which commonly feature a coarse grid due to constraints on available computational capabilities. A measure of the error in the amount of dissolved carbon dioxide introduced by the use of a finite grid is therefore of great interest. In this study, the use of finite-sized grid blocks is shown to overestimate the amount of dissolved carbon dioxide in short-term results by a factor of 1?+?V f/V p, where V f is the grid block volume at the saturation front and V p is the total grid block volume of the plume. This result can be used in a number of ways to correct the calculated short-term dissolution in coarse-scale simulations so that the amount dissolved agrees better with that obtained from fine-scale simulations. 相似文献
3.
In implementing into a molecular dynamics simulation code a simple interionic potential developed to describe the nine component system K2O-Na2O-CaO-MgO-FeO-Fe2O3-Al2O3-TiO2-SiO2 (KNCMFATS), it has been possible to reproduce satisfactorily a number of thermodynamic, structural and transport properties of a representative set of natural silicate melts. An important conclusion reached in this study is the good transferability of the potential from felsic to ultramafic compositions although this transferability becomes less accurate with high silica contents (rhyolitic composition and beyond) and with very iron-rich silicates (e.g. fayalite). A key feature of the simulation is to make the link between macroscopic properties of the melt and its microscopic structure and dynamics. We thus obtain a relationship between the molar volume of the melt, the number of network modifiers and the oxygen coordination number. The simulation also allows one to quantify the coordination environment around the cations as function of the melt composition. Furthermore, the electrical conductivity of the high temperature liquid is investigated. 相似文献
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5.
Isotherms for the sorption of zinc and copper onto kaolinite: comparison of various error functions 总被引：1，自引：0，他引：1
Sh. Shahmohammadi-Kalalagh H. Babazadeh 《International Journal of Environmental Science and Technology》2014,11(1):111-118
In this research, the equilibrium sorption of Zn(II) and Cu(II) by kaolinite was explained using the Freundlich, Langmuir and Redlich–Peterson isotherms, via both linear and non-linear regression analyses. In the case of non-linear regression method, the best-fitting model was evaluated using six different error functions, namely coefficient of determination (r 2), hybrid fractional error function (HYBRID), Marquardt’s percent standard deviation (MPSD), average relative error (ARE), sum of the errors squared (SSE) and sum of the absolute errors (EABS). The examination of error estimation methods showed that the Langmuir model provides the best fit for the experimental equilibrium data for both linear and non-linear regression analyses. The SSE function was found to be a better option to minimize the error distribution between the experimental equilibrium data and predicted two-parameter isotherms. In the case of three-parameter isotherm, HYBRID was found to be the best error function to minimize the error distribution structure between experimental equilibrium data and theoretical isotherms. Non-linear method was found to be more appropriate method for estimating the isotherm parameters. 相似文献
6.
We assessed the performance of a transfer function model for sea-level studies using salt-marsh foraminifera from two estuaries of northern Portugal. An independent data set of 12 samples and 13 sub-fossil samples from a core were used to evaluate if reconstructions and errors derived from current models are adequate. Initial transfer function models provided very strong results as indicated by cross-validation (component 2; r2 = 0.80-0.82; RMSEP ranged from 10.7 to 12.3 cm) and improved its performance by ca. 10% when sample size reached ca. 50. Results derived using an independent test data set indicate that cross-validation is a very effective approach and produces conservative errors when compared to observed errors. We additionally explored the possible effect of transforming the concentration data into percent in the error estimations by comparing the results obtained based on the use of both concentration and compositional data. Results indicate that this type of transformation does not affect the performance of the transfer function. Results derived from a reconstruction of sub-fossil samples from a core indicate that high-resolution sea-level reconstructions are possible, but show that depositional environments have to be selected carefully in order to minimize the impact of possible taphonomical loss. 相似文献
7.
Shahid Manzoor Michael G. Edwards Ali H. Dogru Tareq M. Al-Shaalan 《Computational Geosciences》2018,22(1):195-230
Grid generation for reservoir simulation must honor classical key constraints and be boundary aligned such that control-volume boundaries are aligned with geological features such as layers, shale barriers, fractures, faults, pinch-outs, and multilateral wells. An unstructured grid generation procedure is proposed that automates control-volume and/or control point boundary alignment and yields a PEBI-mesh both with respect to primal and dual (essentially PEBI) cells. In order to honor geological features in the primal configuration, we introduce the idea of protection circles, and to generate a dual-cell feature based grid, we construct halos around key geological features. The grids generated are employed to study comparative performance of cell-centred versus cell-vertex control-volume distributed multi-point flux approximation (CVD-MPFA) finite-volume formulations using equivalent degrees of freedom. The formulation of CVD-MPFA schemes in cell-centred and cell-vertex modes is analogous and requires switching control volume from primal to dual or vice versa together with appropriate data structures and boundary conditions. The relative benefits of both types of approximation, i.e., cell-centred versus vertex-centred, are made clear in terms of flow resolution and degrees of freedom required. 相似文献
8.
Generalized sequential kriging (GSK) for heterogeneous cell size: property modeling without matrices
J. A. Vargas-Guzmán 《Computational Geosciences》2010,14(1):207-215
Sequential kriging avoids the use of matrices and resolves the issue of unstable solutions. It allows for stepwise ways to
get joint estimations and cosimulations that are equivalent to the simultaneous solution. The approach is proposed as the
solution for geocellular modeling with variable cell size from heterogeneous structural properties (HSPs) as required for
modeling with structural constraints. Rock properties are controlled by structural domains, regions, and structural geology
parameters. In some cases, rock properties are cross-correlated to formation thickness, curvature of structures, and other
structural attributes. Cell thickness may be proportional to formation thickness and may enter as a conditioning property
in the estimation of rock property parameters for simulation. In addition, cell volume controls the upscaling of covariance
structures (i.e., regularized variograms). Structural properties are priorly modeled. Perturbation response functions (PRFs)
are computed for each cell vs all possible sample point locations to facilitate sequential kriging. Upscaled PRFs are modified
following conditional updating after each new data value is included in the estimation of parameters. Generalized sequential
kriging is expected to become the main tool for real-time spatial modeling of 3D cellular models with HSP. In addition, some
new developments related to the sequential kriging algorithm are included. Sequential kriging can be used for the estimation
of parameters for simulation in the so-called unstructured grids. 相似文献
9.
多孔介质渗流是普遍的物理过程，涉及地下工程、地热开采、环境工程等各行各业，尤其是工程建设，常面临防渗问题。由于地质条件的复杂性，工程区域地层受到成岩、压实、风化、生物作用等各种影响，故渗流性质复杂，常需要对建设区域的渗流状况进行数值模拟，从而为工程的设计施工提供决策依据。数值仿真结果依赖于对地层介质关键参数的选取,但目前工程多将其视为均匀介质处理，对于介质的非均匀特性考虑较少。文章旨在研究非均质多孔介质渗透率空间分布与等效渗透率的关系。基于连续介质假定、达西定律以及非均匀多孔介质渗透率空间分布函数，建立一维到三维的达西渗流问题模型，通过求解偏微分方程和理论推导，得到基于渗透率空间分布函数的等效渗透率理论表达式，并与有限元计算的数值解进行对比分析，结果表明理论值和数值解误差很小，证明等效渗透率的表达式的合理性。利用该成果可通过多点局部渗透率的测定构建渗透率空间分布函数，从而对整体渗流区域的渗透性质进行快速计算和评估，从而简化异常复杂的工程地质模型以减少计算量需求，对于工程仿真的快速计算和结果评估有重要意义。 相似文献
10.
Molecular dynamics simulations with ab initio potential under various pressures up to 11.58 GPa have been carried out to investigate the relationship between microscopic structure and solubility of Ar in silica melts. The Voronoi diagram method is used to identify interstitial voids in the structure of silica melts. We find that (1) the radius distribution of interstitial voids generally obeys the log-normal probability function; (2) the number of available interstitial voids large enough to accommodate Ar atoms decreases with increasing pressure; (3) Ar solubility increases linearly with pressure up to about 3 GPa, where Ar solubility reaches a maximum value, and then it decreases dramatically when pressure becomes higher than 5-6 GPa. The drop of Ar solubility is a result of structural continuous change but not structural transformation. These results are in good agreement with experimental measurements. 相似文献