基于水力走时反演刻画裂隙含水层非均质性

Characterization of the heterogeneity of a fractured aquifer based on hydraulic travel time inversion

获取含水层水力参数空间非均质分布信息是研究地下水渗流、地下水污染物运移等诸多地下水问题的重要基础。然而,受常规勘察技术所限,含水层的非均质性难以直接刻画,尤其在裂隙介质含水层中,水力参数分布的非均质性更加突出,进一步增加了刻画的难度。针对该问题,本研究首先通过德国哥廷根大学北校区内的Neutra试验场地进行的64次抽水试验,获取了该场地不同深度观测点的水头响应曲线,然后使用解析方法对64组数据进行分析和参数评估,同时采用水力走时的方法对井间水力参数分布进行反演计算,最后将得到的结果分别与经典解析解参数估计和热示踪试验结果进行对比验证。结果表明,解析解参数估计的结果虽然能够在一定程度上展现含水层的垂向非均质性,但是无法刻画井间含水层水力参数的非均质分布;与热示踪试验结果的对比验证了基于水力走时反演的水力层析法在刻画裂隙介质水力参数的空间非均质分布的可靠性。

The spatial distribution of aquifer hydraulic parameters is an important and basic factor to study groundwater seepage,groundwater pollutant transport processes and many other groundwater related problems.However,due to the limitation of conventional exploration technology,the spatial heterogeneity of aquifer hydraulic parameters cannot be described accurately and intuitively.Especially for fractured aquifers,the heterogeneity of hydraulic parameters is much stronger.In order to solve this problem,this study attempts to characterize the hydraulic properties of a fractured aquifer by using travel time based hydraulic tomography.Firstly,the head data at 8 different depths(receivers)in the observation well are recorded through 64 multi-level short-term pumping tests at 8 pumping intervals(sources)in the pumping well with help of double packers performed in Goettingen Germany.All these 64 head response data are used to calculate the hydraulic parameters(K and Ss)with Jacobian analytical solution.Subsequently,the derived hydraulic travel times between each source and receiver are utilized to obtain the hydraulic diffusivity distribution based on hydraulic travel time inversion.For the validation,the inversion results are finally compared with the results from Jacobian analytical solution and thermal tracer test.It shows that the estimated parameters of analytical solution indicate the vertical heterogeneity,but it cannot describe the spatial distribution of these parameters between wells.Results of thermal tracer test have proven the plausibility of the travel time based hydraulic tomography for the characterization of the fractured aquifer.