基于微水试验求解高渗透性承压含水层水文地质参数

Inversion of hydraulic parameters of high permeability confined aquifer based on slug test

为了提高高渗透性承压含水层渗透系数与储水率等水文地质参数的反演精度,科学解释井筒水位的非线性振荡现象,本研究建立了考虑表皮效应和非达西流效应耦合惯性力作用的微水试验模型。模型中表皮效应采用Robbin边界条件描述,非达西流效应采用Forchheimer方程刻画,惯性力作用采用动量平衡方程表达。利用Laplace变换法推导模型的解析解,基于现场试验数据,分析3种因素对反演水文地质参数的影响。结果表明表皮效应、非达西流效应与惯性力作用对参数反演结果的影响均不能忽视。无因次表皮因子(Sw)值、Forchheimer系数(γ)值与瞬时注水后井筒水位与承压含水层隔水顶板之间的垂直距离(l) 3个值越大,井筒水位恢复速度越慢;Sw值越大,井筒水位振荡幅度越小,而γ值和l值越大,井筒水位振荡幅度越大。忽略表皮效应、非达西流效应或惯性力作用均导致渗透系数与储水率的反演结果偏小。研究结果为裂隙承压含水层中水文地质参数的反演提供了一种合理的理论基础和技术依据。

To improve the accuracy of estimated hydraulic parameters such as hydraulic conductivity and specific storage in confined aquifers with high permeability,and provide a scientific explanation for the nonlinear oscillation phenomenon of test well water levels,this study established a slug test model that takes into account the skin and non-Darcy flow effects,as well as inertial force action.The skin effect was described by Robbin boundary conditions and the non-Darcy flow effect was explained by the Forchheimer equation;momentum balance equation expressed the inertial force action.The Laplace transform method was used to derive the analytical solution of this model.Then the impacts of three factors on estimating of hydraulic parameters were analyzed using field data.The results show that the influences of skin effect,non-Darcy flow effect,and inertia force action on the parameter estimation cannot be ignored.More specifically,the higher values of the dimensionless skin factor(Sw),the Forchheimer coefficient(γ),and the vertical distance(l)between the water level in the well and the top of the confined aquifer after instantaneous water injection,the slower rate of water level recovery.As the value of Sw increases,the amplitude of water level oscillation decreases,whereas the amplitudes of water level oscillation increase with larger values ofγand l.Ignoring the skin effect,non-Darcy flow effect or inertia force will lead to underestimating hydraulic conductivity and specific storage.The results can provide theoretical guidance and technical support for the inversion of hydraulic parameters in fractured confined aquifers.