含水层层状非均质对地下水流系统的影响

The impact of aquifer layered heterogeneity on groundwater flow system

区域尺度上含水层非均质具有复杂的结构性和随机性,难以准确刻画,造成非均质对区域地下水流系统的影响机制研究不够深入。本文以鄂尔多斯盆地白垩系地下水流系统为研究实例,选择典型剖面,采用剖面二维随机数值模拟方法,通过对比不同非均质刻画方法下地下水流场的变化,探讨含水层层状非均质对地下水流系统的影响机制。结果显示,均质条件下模型各向异性(含水层水平和垂向渗透系数比值Kh/Kv)取值为1000时,地下水流场与实际条件较为接近;非均质条件下,渗透系数方差取值0.91,水平相关长度取值5000 m,Kh/Kv取值150时,接近实际条件。研究表明,在大尺度地下水流模拟研究中,采用水平相关长度、渗透系数方差和各向异性值三个变量生成的随机场能很好地刻画含水层的层状非均质特征及其对水流系统的影响控制作用。由于含水层不同尺度层状非均质的叠加效应,采用均质各向异性介质等效概化含水层层状非均质性会造成等效各向异性值偏大失真的效应。

Aquifer heterogeneity is an important factor influencing regional groundwater flow patterns.The complex structural and stochastic characteristics of regional-scale aquifer heterogeneity are difficult to characterize,which leads to insufficient understanding of the effects of heterogeneity on groundwater flow systems in practice.In this paper,the Cretaceous groundwater flow system in the Ordos Basin is studied based on the selected typical geological section.Stochastic numerical simulation of the two-dimensional section is employed to analyze the influence mechanism of aquifer layered heterogeneity on groundwater flow systems by comparing the changes of the groundwater flow field under different heterogeneity conditions.The results show that the groundwater flow net is close to the actual conditions when the ratio of horizontal to vertical conductivity(Kh/Kv)is 1000 in model for homogeneous aquifer.It is close to the actual conditions when the variance of conductivity is 0.91,the horizontal correlation length is 5000 m and Kh/Kv is 150 for heterogeneous aquifers.The stochastic simulated aquifer generated by three parameters(i.e.,horizontal correlation length,variance of permeability coefficient,and anisotropy ratio)can well characterize the layered heterogeneity of aquifer and its influence on the groundwater flow systems.Due to the superposition of layered heterogeneity at different scales,equivalent homogeneous,anisotropic model for conceptualizing layered heterogeneous medium in large-scale groundwater flow simulation may lead to a much larger horizontal-to-vertical anisotropy ratio than the ratio between horizontal and vertical correlation scales.