回灌堵塞下的越流承压含水层非达西井流分析

ANALYSIS OF NON-DARCIAN GROUNDWATER FLOW DYNAMICS IN LEAKY CONFINED AQUIFERS UNDER INJECTION CLOGGING DURING RECHARGE

  • 摘要: 针对传统井流模型无法反映井周堵塞与非达西渗流对回灌井流影响的问题,该文采用随时间衰减的渗透系数模型反映井周含水层的堵塞效应,引入Izbash方程描述渗流对达西定律的偏离,建立了考虑回灌堵塞的定流量和定水头完整井回灌非达西井流模型。针对堵塞区与非达西渗流区重合的情形,利用线性化方法和Laplace变换对模型进行了近似半解析求解;而针对堵塞区与非达西渗流区未重合的情形,发展了基于分段非线性Galerkin方法的数值解。分析结果表明:在定流量试验中,较小的渐近渗透系数Knd,∞和较大的堵塞范围rc降低了堵塞区的水头抬升s,但对主含水层几乎没有影响;在定水头试验中,较小的Knd,∞和较大rc降低了整个含水层的s;非达西渗流指数n分别降低定流量试验和提高了定水头试验中的s,并减小了是否考虑堵塞效应的水头差异。此外,回灌堵塞使得定水头和定流量试验的s-logr曲线在r = rc处存在转折,造成定水头试验的s-logt曲线在上升过程中出现下降,上述特征可为回灌堵塞评估与预测提供参考。

     

    Abstract: To address the issue that the traditional well hydraulic models failed to reflect the clogging-induced permeability reduction and the deviation from Darcy’s law, a model for the groundwater hydraulics was developed for constant-rate injection tests (CRTs) and constant-head injection tests (CHTs) in confined aquifers using fully penetrating wells. In the model, a temporally decaying function of time was used for the clogging-related permeability reduction and the Izbash equation was adopted to describe the deviation from Darcy's law of groundwater flow. For the scenario when the clogging region coincides with the non-Darcian flow region, the approximate semi-analytical solution was derived using the linearization procedure and the Laplace transforms; while for scenarios where these regions do not overlap, a numerical solution based on the piecewise nonlinear Galerkin method was developed. A parametric study indicated that: In the CRTs, a smaller asymptotic hydraulic conductivity Knd,∞ and a larger clogging scope rc reduced the hydraulic head increment s in the clogging region and had no effect on flow dynamics in formation zone; whereas in CHTs, a smaller Knd,∞ and a larger rc reduced the s in both the clogging zone and the formation zone; a smaller n leads to smaller s in CRTs but larger s in CHTs and reduces the head difference between models considering and neglecting clogging effects. Besides, the clogging in well vicinity resulted in an obvious inflection point at r = rc on the s-logr curve in both CRTs and CHTs and lead to an apparent decreasing stage of the s-logt curve. These features provide valuable insights for assessing and predicting the evolution of injection clogging.

     

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