Building a three dimensional sealed geological model to use in numerical stress analysis software: A case study for a dam site

The dam area of the SUOXI hydropower project shows high terrain undulation and complex geological conditions, containing 6 faults and 7 weak inter-beds. A geometric model developed to represent the geology and engineering structures should incorporate the geological realities and should allow suitable mesh generation to perform numerical stress analysis. This is an important precondition to perform rock mass stability analysis of a dam foundation based on a numerical stress analysis software such as FLAC^3D. Using the modeling tools available in FLAC^3D, it is difficult to construct a complex geological model even after performing a large amount of plotting and data analyses. The 3-D geological modeling technique suggested in this paper, named as Sealed Geological Modeling (SGM), is a powerful tool for constructing complex geological models for rock engineering projects that require numerical stress analysis. Applying this technique, first, the geological interfaces are constructed for the dam area of SUOXI hydropower project using various interpolation procedures including geostatistical techniques. Then a unitary wire frame is constructed and the interfaces are connected seamlessly. As the next step, a block tracing technique is used to build a geological model that consists of 130 seamlessly connected blocks. Finally, based on the Advancing Front Technique (AFT), each block is discretized into tetrahedrons and a mesh is generated including 57,661 nodes and 215,471 tetrahedrons which is suitable to perform numerical stress analysis using FLAC^3D.     

Continuous Facies Updating Using the Ensemble Kalman Filter and the Level Set Method

We present a methodology based on the ensemble Kalman filter (EnKF) and the level set method for the continuous model updating of geological facies with respect to production data. Geological facies are modeled using an implicit surface representation and conditioned to production data using the ensemble Kalman filter. The methodology is based on Gaussian random fields used to deform the facies boundaries. The Gaussian random fields are used as the model parameter vector to be updated sequentially within the EnKF when new measurements are available. We show the successful application of the methodology to two synthetic reservoir models.     

Integrated geological risk mapping: a qualitative methodology applied in St. Petersburg, Russia

The current active development of the city of St. Petersburg in Russia has led to high growth rates in both industrial and housing areas, causing an increased load on geological media. Taking into account the rather unfavourable geological conditions of the city area, such a development can entail to an intensification of environmental risks. Sustainable and cost-effective land-use planning requires information on geological conditions. Stakeholders need general geological information on the area of St. Petersburg, hydrogeological information on groundwater and information on geological risks. Geological risk maps help to identify whether an area under consideration requires special measures for geological risk management. This paper describes a first attempt to analyze potential geological risks in the city of St. Petersburg, Russia. The approach is to introduce a methodology for multi-risk assessment to be used in land-use planning. The core of the methodology is a matrix that assigns a certain level of geological risk depending on the combination of land use stipulated by the master plan of St. Petersburg and geological characteristics. Based on the matrix, a map presenting potential integrated geological risk can be created. At the same time, the combination of the integrated geological risk map, single geological risk maps and the matrix allows the retracement of which geological characteristics and which land use types contribute to the resulting risk. Users of the methodology in St. Petersburg were trained and an end-user manual was prepared by the authors. The methodology was introduced to professionals who utilize geological information and assess potential risks related to geology.     

Seismic wave propagation in laterally inhomogeneous poroelastic media via BIEM

This work addresses in‐plane pressure P and vertically polarized shear SV seismic wave propagation in a finite, laterally inhomogeneous, multilayered poroelastic geological region resting on the homogeneous elastic half‐space. The particular approach followed here is based on a combination of the (i) viscoelastic approximation (isomorphism) to Biot's equations of dynamic poroelasticity and on the (ii) boundary integral equation method (BIEM) using frequency‐dependent fundamental solutions of the governing wave equations. The problem is formulated under plane strain conditions and time‐harmonic motions are assumed. Validation of the viscoelastic isomorphism and verification of the BIEM is done by solution of benchmark examples. These simulation studies reveal that the proposed methodology is able to depict a sensitivity of the seismic signals recovered to the following parameters: (i) poroelastic properties of fluid saturated layers; (ii) lateral geological inhomogeneity; (iii) surface topography and (iv) frequency content and direction of the incident wave. It is concluded that the combination of viscoelastic isomorphism with BIEM software provides an effective numerical tool for evaluating site‐effect phenomena in multilayered, fluid saturated geological regions with complex geometry. The numerical results obtained demonstrate that dynamic poroelasticity interacting with other physical peculiarities of the Earth's surface layers, such as lateral heterogeneity, material properties along the wave path, local geological profile and type of elastic wave, gives rise to complex seismic signals on the free surface at the site of interest. Copyright © 2010 John Wiley & Sons, Ltd.     

遥感技术在黄土高原区地质灾害详细调查中的应用

黄土高原区地质灾害频发,危害严重,在延安市宝塔区地质灾害详细调查试点中,选用高分辨率的Spot5和快鸟卫星(QuickBird)数据,进行了地质灾害解译与信息提取,获取了丰富的地质环境条件和地质灾害以及承载体信息,为开展地质灾害野外调查提供了基础资料,发挥了遥感技术的先导作用。笔者从遥感调查的内容、数据选择和处理、解译技术方法、地质灾害信息提取、解译及解译效果等方面论述了遥感技术在宝塔区地质灾害详细调查中的应用,认为该技术方法和本次所取得的经验可以在黄土高原区地质灾害详细调查中推广和应用。     

Direct Multiple-Point Geostatistical Simulation of Edge Properties for Modeling Thin Irregularly Shaped Surfaces

Thin, irregularly shaped surfaces such as clay drapes often have a major control on flow and transport in heterogeneous porous media. Clay drapes are often complex, curvilinear three-dimensional surfaces and display a very complex spatial distribution. Variogram-based stochastic approaches are also often not able to describe the spatial distribution of clay drapes since complex, curvilinear, continuous, and interconnected structures cannot be characterized using only two-point statistics. Multiple-point geostatistics aims to overcome the limitations of the variogram. The premise of multiple-point geostatistics is to move beyond two-point correlations between variables and to obtain (cross) correlation moments at three or more locations at a time using training images to characterize the patterns of geological heterogeneity. Multiple-point geostatistics can reproduce thin irregularly shaped surfaces such as clay drapes, but this is often computationally very intensive. This paper describes and applies a methodology to simulate thin, irregularly shaped surfaces with a smaller CPU and RAM demand than the conventional multiple-point statistical methods. The proposed method uses edge properties for indicating the presence of thin irregularly shaped surfaces. Instead of pixel values, edge properties indicating the presence of irregularly shaped surfaces are simulated using snesim. This method allows direct simulation of edge properties instead of pixel properties to make it possible to perform multiple-point geostatistical simulations with a larger cell size and thus a smaller computation time and memory demand. This method is particularly valuable for three-dimensional applications of multiple-point geostatistics.     

Rock media mathematical models processing

This paper reports on mathematical models of rock media processing and on their use in designing open pit coal mines. Spatial mathematical model of rock media was processed on a 25 km² model site, incorporating 918 borehole logs. The model is capable of providing information concerning the geological structure of every point of the investigated area by plotting geological cross-sections along given lines or by plotting contour lines of the surface or the base for thickness of chosen lithological strata. The computation of one point of a grid involves the following steps: Borehole logs are numericaly coded. The geological structure at an arbitrarily chosen pointP is computed as follows. All borehole logs inside the circle (P; R) are used to compute theZ-coordinate of the ground atP by some interpolation formula chosen from those contained in the program system. Next, we check what stratum occurs topmost at boreholes inside the circle and which is most probable as the top stratumC ₁ atP. TheZ-coordinate of theC ₁ stratum surface atP is computed. Then what strata occur underC ₁ stratum and which of them is the most probable stratumC ₂ is determined. The process of computation is repeated until a sequence of strataC _i atP andZ _i coordinates of their surfaces is ascertained. The interpolation formulas included in the system are proper linear combination of PAF (polynomial approximations formulas, linear or quadratic and weighted) and WAF (weighted average formulas). Among the various interpolation formulas, some proved more useful for tectonic fault lines, others for ordinary sedimentary surfaces.     

A model for the conservation of geological remains as documents

 Geological remains are conserved mainly either together with living beings for the sake of the integrity of nature or for their economical or aesthetic value. However, they also have scientific value for the geologist to reconstruct the earth's past. For this reason we propose a model which is an application of marginal utility theory in economics and takes into account the informational utility of geological remains. Informational utility of geological remains ranges over their geological significance which is induced by the importance of the geological processes that produce them, and over their spatial extensiveness. Our model takes into account also the cost and budget of conservation and proposes to solve the differential equations of informational utility and cost simultaneously in order to obtain the optimum quantity of the remains to be conserved. Received: 9 January 1998 · Accepted: 4 February 1998     

三维无缝工程地质建模系统的研制

在边界表示法的基础上,提出了无缝工程地质模型的概念,实现了基于模型线框架的无缝工程地质建模方法,研制了无缝建模系统（ROCKModel）。该系统包括3个部分：原始数据转换工具、实体建模工具与辅助工具,涉及剖分、插值、曲面求交等8个基本功能模块。在基本功能模块的基础上,提出并实现了形态复杂曲面的创建、构建模型线框架、界面编辑与重构、块体搜索、岩体质量三维分级等关键技术。该系统能够实现复杂地质对象与工程对象的无缝建模与可视化,并为数值模拟软件直接提供几何模型。     

Point Cumulative Semivariogram for Identification of Heterogeneities in Regional Seismicity of Turkey

Geological events are neither isotropic nor homogeneous in their occurrences. These two properties present difficulties for spatial modeling of regionalized variables. This paper presents a point cumulative semivariogram (PCSV) technique for quantifying the heterogeneity characteristics of the phenomenon concerned. The basis of the methodology is to obtain experimental PCSVs for each measurement point which led to estimation of radius of influence around each site. In addition, the experimental PCSVs provide basic information about the heterogeneity of the geological variable in the region, and furthermore many useful interpretations can be made concerning the regional variability of the variable. It provides the measure of cumulative similarity of a regional variable around any measurement site. Because PCSV is a means of measuring total similarity, maps at fixed similarity levels are provided in order to document the regional heterogeneity. Identification of heterogeneities depends on the comparison of fixed PCSV values at a multitude of irregularly scattered sites. The PCSV methodology has been applied to the regional seismic data of Turkey.     

Weighted characteristic analysis of spatially dependent mineral deposit data

There are four concepts involved with the methodology used in this analysis: classical second derivative surfaces, boolean representation of the surfaces, determination of weighted model characteristics, and multiple variable regional appraisal.This paper was presented at the International Geological Correlation Program (IGCP) Project 98 entitled Standards for Computer Applications in Resource Studies held at Loen, Norway, September 27–October 1, 1976.     

Computer-aided geometric design of geologic surfaces and bodies

Bivariate quadratic simplicial B-splines are employed to obtain aC ¹-smooth surface from scattered positional or directional geological data given over a two-dimensional domain. Vertices are generated according to the areal distribution of data sites, and polylines are defined along real geological features. The vertices and the polylines provide a constrained Delaunay triangulation of the domain. Note that the vertices do not generally coincide with the data sites. Six linearly independent simplex B-splines are associated with each triangle. Their defining knots and finite supports are automatically deduced from the vertices. Specific knot configurations result in discontinuities of the surface or its directional derivatives. Coefficients of a simplex spline representation are visualized as geometric points controlling the shape of the surface. This approach calls for geologic modeling and interaction of the geologist up front to define vertices and polylines, and to move control points initially given by an algorithm. Thus, simplex splines associated with irregular triangles seem to be well-suited to approximate and allow further geometrically modeling of geologic surfaces, including discontinuities, from scattered data. Applications to mathematical test as well as to real geological data are given as examples.     

Analysing laser‐scanned digital terrain models of gravel bed surfaces: linking morphology to sediment transport processes and hydraulics

The grain‐scale topography of a sediment surface is a key component of a fluvial system, affecting aspects including sediment transport, flow resistance and ecology. However, its effect is hard to quantify because of the need for grain‐scale elevation data from in situ fluvial gravel surfaces which are difficult to collect. The sediment surface properties are, therefore, commonly estimated as a function of the sediment grain‐size distribution; however, because of additional factors, such as grain packing and shape, there is not necessarily a unique relationship between the two. A new methodology has been developed that uses terrestrial laser scanning to collect grain‐scale topographic data from in situ fluvial gravel surfaces, from which digital terrain models are created. This paper investigates methods of analysing such digital terrain models, and possible sedimentological interpretations that can be drawn from the analysis. Eleven digital terrain models from exposed gravel surfaces in two contrasting rivers (the River Feshie and Bury Green Brook) were analysed by calculating: the distribution of surface elevations, semivariograms, surface inclinations, surface slopes and aspects and grain orientation. The distribution of surface elevations and surface slope and aspect analysis were found to be most informative. In the River Feshie, grain‐size was interpreted as being a dominant control on sediment surface structure and gravel imbrication was identified. In Bury Green Brook, the location of the digital terrain models within the riffle–pool sequence was the dominant control on surface structure and grain orientation. Such digital terrain models therefore provide a new approach to measuring and quantifying the topography of fluvial sediment surfaces.     

Geology-exploration endowment models for simultaneous estimation of discoverable mineral resources and endowment

A new type of model, referred to as a geology-exploration endowment model, is proposed in this paper. These models differ from conventional ones in that they simultaneously estimate discoverable mineral resources and endowment by extracting and utilizing geoscience information from both geological features and exploration factors. Geological measurements describe mineral endowment, while exploration variables describe the completeness of exploration, and together, they explain discoverable resources. Without incorporation of exploration factors to geological-endowment models, the estimation of endowment is generally biased. This paper presents two variations of such hybrid nonlinear models: Poisson-logistic (PL) and exponential-logistic (EL) for estimation of number of mineral deposits or prospects based upon the Arps and Roberts' discovery process model and assumptions of endowment distributions. The PL model is obtained by assuming that endowment follows a Poisson distribution and that the probability of mineral occurrences ( 1) is a logistic function with geological arguments. The EL model is derived similarly, except that endowment is assumed to be exponentially distributed. The PL model is demonstrated on both a synthetic example and a case study of epithermal gold-silver vein deposits in the Walker Lake quadrangle of Nevada and California. A map containing the estimated numbers of gold-silver mineral occurrences potentially discoverable in the Walker Lake quadrangle is produced. The parameter estimates for the PL model based on the Levenberg-Marquardt iterative algorithm are validated by using several statistical measures, such as theT-statistic, Box's bias, and goodness of fit. Both a synthetic example and a case study suggest that the Box's bias measure is useful for validation of the nonlinear estimates.     

An index to represent lateral variation of the confidence of experts in a 3-D geological model

A Confidence Index is proposed that expresses the confidence of experts in the quality of a 3-D model as a representation of the subsurface at particular locations. The Confidence Index is based on the notion that the variation of the height of a particular geological surface represents general geological variability and local variability. The general variability comprises simple trends which allow the modeller to project surface structure at locations remote from direct observations. The local variability limits the extent to which borehole observations constrain inferences which the modeller can make concerning local fluctuations around the broad trends. The general and local geological variability of particular contacts are modelled in terms of simple trend surfaces and variogram models. These are then used to extend measures of confidence that reflect expert opinion so as to assign a confidence value to any location where a particular contact is represented in a model. The index is illustrated with an example from the East Midlands region of the United Kingdom.     

On the problem of boundary conditions in isentropic coordinates

The main advantages of constant potential enthalpy as a vertical coordinate are weaker horizontal velocity gradients in frontal regions and a higher vertical resolution. A disadvantage is the intersection of isentropes with the ground and folding of these surfaces. A numerical model is proposed to overcome the difficulties imposed by the intersection of isentropes with the ground. The model contains a physical and computational domain. The top and bottom surfaces of the computational domain are isentropes whereas the physical domain of the flow confined above by a free surface of constant pressure, and the bottom of this domain is the surface of the earth. In the present study the top surfaces of these two domains coincide (θ _T, P_Tare constants in space and time). The model was tested for the study of frontogenesis and cyclogenesis and integrated for 7 days. The results correspond to enstrophy-conserving finite difference scheme.     

一种基于反距离加权方法的层状三维地质界面拟合算法

三维空间中地质曲面模拟是矿产勘查、大比例尺成矿预测等地学领域的重要研究内容之一.与地球化学、地球物理数据的曲面拟合相比,地质界面拟合更加复杂且具有一般性.从功能需求角度出发,地质界面拟合需要处理层状地层、不整合地层以及存在构造的地层等多种情况;从算法实现角度讲,该拟合过程不同于物化探数据通过某一属性值进行曲面拟合的情况,因为在地质界面模拟过程中,不存在这样的特征值进行曲面拟合,因此不能直接使用物化探数据等值面提取的思想模拟地质接触界面.针对上述问题,提出了一种基于反距离加权法移动立方格算法的层状地层曲面拟合算法.该方法模型适合绝大多数层状地学三维曲面模拟.     

甘肃省花牛山幅1:50 000矿产地质图数据库

甘肃省花牛山幅（K46E017023）1：50 000矿产地质图是根据《矿产地质调查技术要求（1：50 000）》和行业的统一标准及要求,在充分利用1：200 000、1：50 000等区域地质调查工作成果资料的基础上,采用数字填图系统进行野外地质专项填图,并应用室内与室外填编图相结合的方法完成的。本图对南华系-震旦系洗肠井群、寒武系西双鹰山组、奥陶系花牛山群的建造类型进行了重新划分,把图幅内侵入岩时代归纳为晚奥陶世—早志留世、泥盆纪、晚三叠世等3期,建立了岩浆岩的演化序列。本数据库包含12个地层单位和3期岩浆岩资料,数据量约为3.77 MB。这些数据充分反映了1：50 000矿产地质调查示范性成果,对该区矿产资源研究、能源勘探等具参考意义。