Stochastically conditioned flow paths and travel time distribution in highly heterogeneous synthesized aquifers / Chemins d’écoulement et distribution des temps de parcours au sein d’aquifères synthétiques hautement hétérogènes sous conditions stochastiques

Abstract

Abstract Characterization of heterogeneity at the field scale generally requires detailed aquifer properties such as transmissivity and hydraulic head. An accurate delineation of these properties is expensive and time consuming, and for many if not most groundwater systems, is not practical. As an alternative approach, stochastic representation of random fields is used and presented in this paper. Specifically, an iterative stochastic conditional simulation approach was applied to a hypothetical and highly heterogeneous pre-designed aquifer system. The approach is similar to the classical co-kriging technique; it uses a linear estimator that depends on the covariance functions of transmissivity (T), and hydraulic head (h), as well as their cross-covariances. A linearized flow equation along with a conditional random field generator constitutes the iterative process of the conditional simulation. One hundred equally likely realizations of transmissivity fields with pre-specified geostatistical parameters were generated, and conditioned to both limited transmissivity and head data. The successful implementation of the approach resulted in conditioned flow paths and travel-time distribution under different degrees of aquifer heterogeneity. This approach worked well for fields exhibiting small variances. However, for random fields exhibiting large variances (greater than 1.0), an iterative procedure was used. The results show that, as the variance of the ln[T] increases, the flow paths tend to diverge, resulting in a wide spectrum of flow conditions, with no direct discernable relationship between the degree of heterogeneity and travel time. The applied approach indicates that high errors may result when estimation of particle travel times in a heterogeneous medium is approximated by an equivalent homogeneous medium.     

Evaluating the quality of hydraulic conductivity estimates from piezometer slug tests in peat

Although widely used in wetland hydrological studies, hydraulic conductivity (K) estimates from piezometer slug tests are often of questionable validity. Frequently, this is because insufficient attention is paid to the details of the test procedure. Further, in a potentially heterogeneous and anisotropic medium such as peat, the use of slug tests is prone to error. In this paper we address some of the methodological issues surrounding piezometer slug tests in peat. We compare slug test data with laboratory determinations of vertical and horizontal K obtained using a new method. Piezometers were installed at three depths in a floodplain fen peat in Norfolk, UK. Slug tests were initiated by both slug insertion and slug withdrawal, and repeat tests were conducted to examine the robustness of our K estimates. Most of the tests displayed departures from the log‐linear model of Hvorslev, the form of departure being consistent with compressible soil behaviour. The results suggest that insertion tests gave similar results to those initiated by withdrawal. Repeat testing showed that withdrawal data, in particular, gave highly reproducible normalized responses that were independent of the initial head. Values for K estimated using the slug tests were in the range 1 × 10⁻⁴ to 1·6 × 10⁻³ cm s⁻¹, which is towards the upper end of the range reported for peats generally. Laboratory tests yielded similar values of K to those obtained from the slug tests. Although the laboratory tests showed that the peat was anisotropic, the K values generated by slug testing proved relatively good estimates of both vertical and horizontal K. Copyright © 2005 John Wiley & Sons, Ltd.     

Transport and retention of Escherichia coli in a mixture of quartz,Al‐coated and Fe‐coated sands

Transport and retention of Escherichia coli through the mixture of quartz, Al‐coated and Fe‐coated sands was examined using column experiments to investigate the effect of geochemical heterogeneity on bacteria transport. The first set of the experiments was performed in quartz, Al‐coated and Fe‐coated sand mixtures (coated sand: 0, 5, 10, 25, 50, 100%) to examine the influence of positively‐charged sand grains on bacteria transport. The second experiments were carried out to observe the impact of pH (range 6·74–8·21) on bacteria transport in the mixture of quartz 50% and Fe‐coated sand 50%. The third experiments were conducted to analyse the effect of ionic strength (0, 50, 100, 200 mM) on bacteria transport in the mixture of quartz 50% and Al‐coated sand 50%. The first experiments show that bacterial mass recoveries were in the range of 3·6–43·4%, decreasing nonlinearly as the content of Al‐ and Fe‐coated sands increased. In the second experiments, the bacterial mass recoveries were in the range of 35·5–79·2%, increasing linearly as the solution pH increased. In the third experiments, the mass recovery was 3·4% at 0 mM. As the ionic strength increased to 50mM, the mass recovery decreased to 0%. When the ionic strength increased further to 100 and 200 mM, no bacterial mass was recovered as in the case of 50 mM. It indicates that in the mixed medium of quartz 50% and Al‐coated sand 50% both positive (increment of bacterial adhesion) and negative (decrement) effects of ionic strength may be counterbalanced, minimizing the impact of ionic strength on the bacterial adhesion. This study helps to understand the role of metal oxides and solution chemistry in the transport of bacteria in geochemically heterogeneous media Copyright © 2008 John Wiley & Sons, Ltd.     

Assessing radial transmissivity variation in heterogeneous aquifers using analytical techniques

Pumping tests are one of the most commonly used in situ testing techniques for assessing aquifer hydraulic properties. Numerous researches have been conducted to predict the effects of aquifer heterogeneity on the groundwater levels during pumping tests. The objectives of the present work were as follows: (1) to predict drawdown conditions and to estimate aquifer properties during pumping tests undertaken in radially symmetric heterogeneous aquifers, and (2) to identify a method for assessing the transmissivity field along the radial coordinate in radially symmetric and fully heterogeneous transmissivity fields. The first objective was achieved by expanding an existing analytical drawdown formulation that was valid for a radially symmetric confined aquifer with two concentric zones around the pumping well to an N concentric zone confined aquifer having a constant transmissivity value within each zone. The formulation was evaluated for aquifers with three and four concentric zones to assess the effects of the transmissivity field on the drawdown conditions. The specific conditions under which aquifer properties could be identified using traditional methods of analysis were also evaluated. The second objective was achieved by implementing the inverse solution algorithm (ISA), which was developed for petroleum reservoirs to groundwater aquifer settings. The results showed that the drawdown values are influenced by a volumetric integral of a weighting function and the transmissivity field within the cone of depression. The weighting function migrates in tandem with the expanding cone of depression. The ability of the ISA to predict radially symmetric and log‐normally distributed transmissivity fields was assessed against analytical and numerical benchmarks. The results of this investigation indicated that the ISA method is a viable technique for evaluating the radial transmissivity variations of heterogeneous aquifer settings. Copyright © 2013 John Wiley & Sons, Ltd.     

Three-dimensional bounding surface architecture and lateral facies heterogeneity of a wet aeolian system: Entrada Sandstone,Utah

Aeolian deposits form noteworthy reservoirs (for example, Norphlet Formation and Rotliegend Group) in hydrocarbon extraction and carbon capture and storage contexts, but stratigraphic architecture imparts significant heterogeneity. Bounding surfaces result from autogenic and allogenic controls and can represent important changes in dune-field dynamics. To further evaluate the impacts of facies heterogeneity and flow-inhibiting bounding surfaces on reservoir performance and reconstruct ancient erg evolution, the stratigraphic architecture of aeolian systems must continue to be studied at multiple scales. This study pairs traditional methods (for example, measured stratigraphic sections) with advanced technologies (for example, drone-derived outcrop models) to precisely resolve the metre to kilometre-scale three-dimensional stratigraphic architecture of wet aeolian Middle Jurassic Entrada Sandstone outcrops located at Rone Bailey Mesa near Moab, Utah, USA. Five facies are identified, primarily based on sedimentary fabrics, and are grouped into three associations named dune, sabkha and sand sheet. Statistical analyses of gamma-ray spectrometer and automated mineralogy data indicate a distinct mineralogical difference between dune (quartz-rich) and sabkha (more feldspathic) packages, suggesting that gamma-ray logs may be used to better predict facies distribution in the subsurface. Seven modelled super bounding surfaces are planar to undulatory, with no perceived spatial trends. Five modelled interdune migration surfaces are undulatory but exhibit an average 0.09° angle of climb roughly parallel to the palaeocurrent direction. Two modelled superposition surfaces are linear to sinuous in plan-view. Laterally discontinuous sabkha packages observed are interpreted to be remnants of closed, damp, interdune flats located between ca 8.5 to 17.0 m tall, sinuous, transverse bedforms or patches of such bedforms. Based on stratigraphic architecture interpretations, the Entrada Sandstone preserves signals of allogenic forcing and localized autogenic bedform cannibalization of the substrate. The findings of this study, some of which are not commonly recognized in wet aeolian facies models, enhance the understanding of erg evolution and can parameterize static models of aeolian reservoirs.     

基于语义分割深度学习的找矿靶区预测研究——以广东省阳江-茂名地区为例

找矿靶区预测需要综合考虑地质背景、地球化学数据、地球物理勘探数据、遥感数据等因素。随着人工智能时代的到来,靶区预测可以最大限度地利用计算机运算性能,通过特定的规则集成所有地学数据对各类矿种的找矿靶区进行预测,尽可能规避由于数据种类多、数据量大、方法复杂、主观性强造成的预测结果可靠性差等问题。本文以广东省阳江-茂名地区为例,融合地球化学、地层岩性、地质构造、地形地貌等数据,基于PSPNet、SegNet、UNet三种语义分割深度学习模型进行预测,结果表明PSPNet模型在预测精度方面优于SegNet及UNet模型,并预测出了55处铁矿、金矿、铜矿、高岭土矿找矿靶区,其中79.7%的已查明矿点位于预测靶区内,表明该方法在找矿靶区预测中具有较高的可行性,可以用于找矿勘查并圈定靶区。     

卷积神经网络和视觉注意力语义分割模型在高分辨率遥感影像分类中的性能分析

随着深度学习语义分割的快速发展,基于计算机视觉语义分割模型的高分辨率遥感影像分类方法也大量涌现。为系统定量地研究经典的和先进的视觉语义分割模型在遥感影像分类中的性能,在总结深度学习语义分割进展的基础上,选择9种基于卷积神经网络(CNN)和视觉注意力的语义分割算法,对米级和厘米级2个尺度的遥感数据集进行分析研究。在模型构建上基于计算机视觉通用的语义分割框架,训练时采用红绿蓝3波段遥感图像并基于ImageNet预训练权重进行迁移学习训练。研究结果表明：通用的语义分割模型通过常规训练设置进行训练能取得较好的遥感影像分类效果,部分地物的交并比(IoU)可以达到90%以上;基于视觉注意力的遥感影像分类模型的精度普遍高于基于CNN的模型,且MaskFormer能更有效地提取离散的地物信息;不同类别的精度最高值并不全在总体最优模型中,部分会存在于次优模型中;类似的地物在更高分辨率遥感数据集中可以获得更高的精度。     

Detecting subpixel deciduous components to complement traditional land cover classifications in Southwest Finland

To ensure successful conservation of ecological and cultural landscape values, detailed and up-to-date spatial information of existing habitat patterns is essential. However, traditional satellite-based and raster classifications rely on pixels that are assigned to a single category and often generalized. For many fragmented key habitats, such a strategy is too coarse and complementary data is needed. In this paper, we aim at detecting pixel-wise fractional coverage of broadleaved woodland and grassland components in a hemiboreal landscape. This approach targets ecologically relevant deciduous fractions and complements traditional crisp land cover classifications. We modeled fractional components using a k-NN approach, which was based on multispectral satellite data, assisted by a digital elevation model and a contemporary map database. The modeled components were then analyzed based on landscape structure indicators, and evaluated in conjunction with CORINE classification. The results indicate that both broadleaved forest and grassland components are widely distributed in the study area, principally organized as transition zones and small patches. Landscape structure indicators show a substantial variation based on the fractional threshold, pinpointing their dependency on the classification scheme and grain. The modeled components, on the other hand, suggest high internal variation for most CORINE classes, indicating their heterogeneous appearance and showing that the presence of deciduous components in the landscape are not properly captured in a coarse land cover classification. To gain a realistic perception of the landscape, and use this information for the needs of spatial planning, both fractional results and existing land cover classifications are needed. This is because they mutually contribute to an improved understanding of habitat patterns and structures, and should be used to complement each other.     

基于图的语义室内导航模型构建研究

室内空间模型是室内导航的基础和关键所在,针对当前多数室内空间模型在建模过程中只考虑部分导航相关的影响因素,适用范围有限这一问题,结合室内导航特点,综合考虑用户室内移动特征、几何和语义信息表达、路径规划效率3个方面的建模影响因素,提出一种基于图的语义室内导航模型。基于图论的方法构建室内导航概念模型,然后在概念模型的基础上提出具体的几何图模型构建方法和语义信息表达方式,设计图模型中节点和边的数据结构,最后研究将该模型用于不同情景下室内路径规划的具体流程。