Numerical modeling of reservoirs or pipes in groundwater seepage

In groundwater studies, the numerical modeling of complex boundary conditions can be made easier by considering reservoirs and pipes as “reservoir” finite elements, which can store or release large volumes of water at almost constant hydraulic head. The numerical code to be used must solve the complete conservation equation with unlinked functions for the water retention curve and the unsaturated hydraulic conductivity, and the ability to describe these as step functions. Four examples illustrate the performance of the “reservoir” element: reservoir pumping, laboratory variable-head permeability test, vertical flow in an open borehole, and pumping test with well storage.     

基于ANSYS与OpenGL的高速公路结构物仿真建模及三维地层地表修剪方法

现代三维视景建模与仿真技术在高速公路工程选线、施工以及运营管理中具有良好的应用前景。结构物的仿真建模以及能反映施工前后地表形态变化的三维地层模型研究是高速公路信息化中的重要问题。介绍了一种借用ANSYS有限元分析软件提取结构物三维模型表面几何信息的简便方法;结合OpenGL纹理贴图技术,实现了结构物的仿真建模;针对结构物施工后对地表形态改变较大的问题,提出利用结构物表面数据对三维地层模型地表网格进行修剪的方法--地表网格竖直投影修剪法。把上述方法应用到广东省某高速公路高边坡的三维视景仿真建模中,结果表明,边坡的仿真模型较逼真。三维地层模型修剪后的地表形态与真实情况接近,验证了方法的合理性、可靠性。     

周家湾地区前侏罗纪古地貌恢复及油气富集规律

前侏罗纪古地貌控制着中下侏罗统沉积发育及油气的富集规律, 精确恢复刻画古地貌形态对于侏罗系油气勘探至关重要.以鄂尔多斯盆地周家湾地区为例, 在沉积相、砂体展布、古流向物源、古厚度恢复、古水深校正等分析的基础上, 结合地质、钻井、测井等解释资料, 应用三维储层建模技术, 定性定量地对前侏罗纪古地貌进行了恢复.同时建立了三维砂体、孔隙度、渗透率模型, 从生、储、盖、圈、运、保等油气成藏条件, 直观地解释了古地貌油气富集规律.依据以上模型, 预测出油气有利储集区分布在三大斜坡储集带的河流边滩砂体和河谷内的心滩处, 为勘探开发提供了可靠依据.      

一种基于面模型的巷道三维自动建模方法研究

研究了一种基于面模型的矿山巷道三维自动建模方法。巷道建模分解为网络建模、断面建模、巷道段建模以及空间交汇几个步骤。对建模过程涉及的各算法进行了分析,基采用C++编程实现整个建模过程,并总结了有待进一步研究的问题。     

构造应力环境对浅成岩体成矿系统的制约:从安庆月山岩体冷却过程动力学计算模拟结果分析

为探讨构造应力环境对浅成岩体成矿系统的制约,以安庆地区的月山岩体及其所形成的安庆铜矿床为例,在传统地质调查研究的基础上,通过假设不同的力学边界条件进行岩体冷却过程动力学的计算模拟实验研究。计算结果显示,在没有构造应力作用时,在岩体的接触带上不可能形成有利成矿定位的局部汇流扩容空间,挤压和拉伸作用都能够在岩体接触带形成局部汇流扩容空间,但二者的空间分布规律有着极大的差别,只有拉伸构造应力作用下的动力学计算模拟实验能在已发现矿体部位形成汇流扩容空间,表明构造应力环境对成矿定位的汇流空间的制约以及拉伸构造应力作用对月山岩体成矿的重要贡献。在拉伸构造应力和无构造应力作用时,接触带上的流体压力都是随着变形的进程而趋降低的,只有在挤压构造应力作用下,流体压力才会有一个超压的过程,流体超压是形成斑岩型矿床的重要机制。可见挤压环境才是一种有利于斑岩型矿床成矿的构造环境,铜陵-安庆地区缺乏与矽卡岩矿床相对应的斑岩型矿床主要原因之一是成矿时处于一种拉伸的构造应力作用环境。     

FLAC数值模拟软件及其在地学中的应用

FLAC是以拉格朗日差分法为基础的一种数值模拟应用软件,主要用于岩土力学工程。近年地质学家将其应用到地质构造和块体运动学、动力学研究中,以证实或证伪地球学家们提出的相关地球动力学模型。本文初步介绍了FLAC应用软件的基本原理、使用方法以及它在国内外地质学上的几个应用实例。     

Development of groundwater modeling for the Azraq Basin, Jordan

 The three-dimensional groundwater flow model MODFLOW was applied to simulate water level change in the complex multi-aquifer systems (the Upper and Middle Aquifers) of the Azraq basin. The model was calibrated by matching observed and simulated drawdown for steady and transient states over the period 1970–1992. Drawdown data for the period 1993–1997 were used to test the model's ability to predict the response of the aquifers. The model performed well in representing the water level contours of the Upper and Middle Aquifers for steady state calibration. Agreement between the observed and simulated drawdowns was obtained for transient state calibration. To predict the aquifer system responses for the period of 1997–2025, four different pumping schemes (scenarios) have been investigated. The first scenario (present pumping rate) reveals that there will be approximately a 25 m drop in the water level at the well-field area in 2025. However, the worst scenario (pumping rate at 1.5 times the present rate) reveals an approximate 39 m drop in the water level at the well-field area in 2025. The safe yield for the Upper Aquifer System was found to be about 25 million cubic meters (MCM) yearly. Received: 24 June 1999 · Accepted: 30 November 1999     

A multi-method approach to study the stability of natural slopes and landslide susceptibility mapping

In this paper, a multi-method approach for the assessment of the stability of natural slopes and landslide hazard mapping applied to the Dakar coastal region is presented. This approach is based on the effective combination of geotechnical field and laboratory works, of GIS, and of mechanical (deterministic and numerical) stability analysis. By using this approach, valuable results were gained regarding instability factors, landslide kinematics, simulation of slope failure and coastal erosion. This led to a thorough assessment and strong reduction in the subjectivity of the slope stability and hazard assessment and to the development of an objective landslide danger map of the SW coast of Dakar. Analysis of the results shows that the slides were influenced by the geotechnical properties of the soil, the weathering, the hydrogeological situation, and the erosion by waves. The landslide susceptibility assessment based on this methodological approach has allowed for an appropriate and adequate consideration of the multiple factors affecting the stability and the optimization of planning and investment for land development in the city.     

Possible impact of shallow interfluve traps on groundwater remediation

Shallow stratigraphic traps exist in certain geologic environments, which might complicate groundwater remediation efforts. Too often, pump-and-treat remediation wells are installed in geometric patterns designed to maximize cleanup operations. If, however, shallow stratigraphic traps are present, certain contaminants may be locally trapped and thus missed during cleanup operations. Alternatively, if shallow stratigraphic traps are delineated prior to location of cleanup wells, fewer wells may be needed for remediation. For example, a single well located at the trap apex, coupled with a single injection well, might be sufficient if: (1) all contaminants were contained in the trap, and (2) the trap was not laterally extensive. Interfluve stratigraphic traps are formed when braided outwash sands are subsequently covered by backswamp or lacustrine clay deposits. Such traps are common near-surface features of the valley train deposits of the Lower Mississippi River Valley and have relief of a few tens of centimeters to perhaps in excess of 10 m. Interfluve traps are also expected to commonly occur in many glaciated regions. Due to channel migration during backswamp clay deposition, and differing thicknesses of clay cover, it is unlikely that all interfluve traps can be delineated by a single method. Therefore, several geological techniques that might be useful in delineating shallow interfluve traps are briefly discussed here, as well as potential complications in using the described methods.     

Recharge areas and geochemical evolution of groundwater in an alluvial aquifer system in the Sultanate of Oman

A regional hydrogeochemical model was developed to evaluate the geochemical evolution of different groundwaters in an alluvial aquifer system in the Interior of Oman. In combination with environmental isotopes the model is able to extract qualitative and quantitative information about recharge, groundwater flow paths and hydraulic connections between different aquifers. The main source of water to the alluvial aquifer along the flow paths of Wadi Abyadh and Wadi Muaydin in the piedmont is groundwater from the high-altitude areas of the Jabal Akhdar and local infiltration along the wadi channels. In contrast, the piedmont alluvial aquifer along Wadi Halfayn is primarily replenished by lateral recharge from the ophiolite foothills to the east besides smaller contributions from the Jabal Akhdar and local infiltration. Further down gradient in the Southern Alluvial Plain aquifer a significant source of recharge is direct infiltration of rain and surface runoff, originating from a moisture source that approaches Oman from the south. The model shows that the main geochemical evolution of the alluvial groundwaters occurs along the flow path from the piedmont to the Southern Alluvial Plain, where dedolomitization is responsible for the observed changes in the chemical and carbon isotope composition in these waters.

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Resumen Un modelo hidrogeoquímico regional fue desarrollado, para evaluar la evolución geoquímica de diferentes aguas subterráneas en un sistema acuífero aluvial ubicado en el interior de Omán. El modelo, en combinación con isótopos ambientales, es capaz de obtener información cualitativa y cuantitativa sobre recarga, direcciones de flujo de agua subterránea y sobre las conexiones hidráulicas entre diferentes acuíferos. La fuente principal de agua para el acuífero aluvial en el piedemonte son las aguas subterráneas, a lo largo de las direcciones de flujo del Wadi Abyadh y del Wadi Muaydin, desde las áreas de gran altura de Jabal Akhdar y como infiltración local a lo largo de los canales del wadi. En contraste, el acuífero aluvial del piedemonte a lo largo del Wadi Halfayn, esta alimentado principalmente por recarga lateral desde las partes bajas de las montañas de ofiolitas hacia el Este, además por pequeñas contribuciones desde el Jabal Akhdar e infiltración local. Siguiendo gradiente abajo en el acuífero de la Llanura Aluvial del Sur, allí tanto la infiltración directa de lluvia, como la escorrentía superficial constituyen fuentes significativas de recarga, las cuales se originan en una fuente de humedad que llega a Omán proveniente del Sur. El modelo muestra, que la evolución geoquímica principal de las aguas subterráneas en el aluvión, sucede a lo largo de la dirección de flujo, que va desde el piedemonte hacia la Llanura Aluvial Sur, en donde el proceso de des-dolomitización es el responsable de los cambios observados en la composición química y también del contenido de isótopos de carbono en estas aguas.

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Résumé On a développé un modèle régional hydrogéochimique pour évaluer lévolution géochimique des différentes eaux souterraines dans le système aquifère de lintérieur dOman. Avec la contribution des isotopes denvironnement, le modèle est capable de fournir des informations qualitatives et quantitatives sur la recharge, les directions découlement et sur les connections hydrauliques entre les différents aquifères du système. La source principale pour laquifère situé au long de la direction découlement des oueds de Abdyah et de Muaydin dans le piémont est leau souterraine provenant des zones de haute altitude de Jabal Akhbar ainsi que linfiltration locale au long des canaux de loued. Par contre, à part dune petite contribution provenant des infiltrations locaux et de Jabal Akhbar, l aquifère alluvial de Wadi Halfayan est en principal alimenté par la recharge latérale provenant des ophiolites situées dans la partie est. Les plus importantes sources de recharge dans laval de laquifère de la Plaine Alluviale sont linfiltration directe et le ruissellement provenant dune source dhumidité qui sapproche dOman par le sud. Le modèle montre que la principale évolution géochimique se produise au long de la direction découlement qui part de piémont de la Plaine Alluviale du Sud, où le procès de dédolomisation est responsable pour les changements observés dans la composition géochimique et en carbone des eaux.