GROUNDWATER-FLOW AND SAND BODY INTERCONNECTEDNESS IN A THICK, MULTIPLE-AQUIFER SYSTEM
GROUNDWATER-FLOW AND SAND BODY INTERCONNECTEDNESS IN A THICK, MULTIPLE-AQUIFER SYSTEM
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DOI：
10.1029/wr022i005p00679
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发表时间：
1986-05-01
影响因子：
5.4
通讯作者：
FOGG, GE
中科院分区：
文献类型：
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作者：
FOGG, GE
许多所谓的砂岩含水层实际上是多含水层系统，由复杂分布在低渗透性粉土和粘土基质中的不连续砂体组成。这些不同的岩相的安排和相互联系强烈影响的水力传导率（K）的空间格局，反过来，地下水流量和质量输运。一个有前途的技术，估计这种模式的K涉及仔细分析地下地质和地下水文数据。在这项研究中，利用来自岩心样品和抽水试验的K数据以及100多个地球物理日志，对德克萨斯州Wilcox含水层系统部分的数值流模型进行了K的三维分布估计。含水层系统厚达320米，由河流环境中沉积的多个细长砂体、粉砂和粘土组成，与墨西哥湾沿岸和其他沉积盆地中发现的许多其他系统相似。由此产生的确定性-概念性流动模型展示了在地下水模型中纳入地质信息的重要性和方法。含水层中的流动被证明与其说是由K的砂，其连续性和互连性控制。大部分含水层系统由大型区域组成，其中河道充填砂稀疏且明显不连通，导致地下水流速比相邻的、相互连通良好的河道充填砂带低101至103倍。模拟结果也提出了严重的怀疑，我们的能力，预测区域规模的流量和质量运输复杂的含水层，如威尔科克斯，使用目前的技术。尽管砂体连通性至关重要，但也很难估计。一个或两个连接良好的砂体在一个系统中，否则断开砂体可以完全改变速度场。如果砂体垂直连接且存在非零垂直水力梯度，则尤其如此。由于该模型是三维模型，水头对异质性或连通性的敏感性远低于二维模型中通常观察到的敏感性，因此该模型计算的水头几乎没有指示良好连通区域的位置。因此，这些区域很容易被检测到，即使在精心校准的模型，产生合理准确的水头。这是溶质运移模拟的一个重要方面。
Many so‐called sandstone aquifers are actually multiple‐aquifer systems consisting of discontinuous sand bodies distributed complexly in a matrix of lower‐permeability silts and clays. The arrangement and Interconnectedness of these various lithofacies strongly influence spatial patterns of hydraulic conductivity (K) and, in turn, groundwater flow and mass transport. A promising technique of estimating such patterns ofKinvolves careful analysis of both subsurface geologic and subsurface hydrologic data. In this study the three‐dimensional distribution ofKwas estimated for a numerical flow model of part of the Wilcox aquifer system in Texas, usingKdata from core samples and pumping tests and more than 100 geophysical logs. The aquifer system, which is up to 320 m thick, consists of multiple, elongate sand bodies and silts and clays deposited in a fluvial environment and is similar to many other systems found in the Gulf Coast and other sedimentary basins. The resulting deterministic‐conceptual flow model demonstrates the importance and methods of incorporating geologic information in groundwater models. Flow in the aquifer is shown to be controlled not so much byKof the sands as by their continuity and Interconnectedness. Much of the aquifer system consists of large zones in which the fluvial channel‐fill sands are sparse and apparently disconnected, resulting in groundwater flow rates lower by a factor of 101to 103than in adjacent, well‐interconnected belts of fluvial channel‐fill sand belts. Modeling results also raise serious doubts regarding our ability to predict regional scale flow and mass transport in complex aquifers such as the Wilcox, using current technology. Though sand body Interconnectedness is critically important, it is also very difficult to estimate. One or two well‐connected sands among a system of otherwise disconnected sands can completely alter a velocity field. This is particularly true if the sands are connected vertically and nonzero vertical hydraulic gradients exist. Because the model is three‐dimensional, sensitivity of hydraulic head to heterogeneity or Interconnectedness is much less than normally observed in two‐dimensional models, and therefore heads computed by the model give little to no indication of the location of well‐interconnected zones. Thus such zones can easily go undetected, even in carefully calibrated models which yield reasonably accurate hydraulic heads. This is a significant point for modeling of solute transport.