The response of hydraulic conductivity to air-trapped saturation in a dissolution process of trapped-air in quasi-saturated fine sands media
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摘要:
准饱和含水层的渗透系数会随着圈闭气体饱和度的增大而变小，但受限于试验操作和测量精度，通过传统驱替试验很难获得大量连续的圈闭气体饱和度数据，因此限制了小圈闭气体饱和度及其对应的准饱和渗透系数之间关系的准确刻画。研究设计了一个以氧气代替天然圈闭过程中空气的准饱和细砂圈闭气体溶解试验，通过精确测量溶解过程中水中可溶性氧和相应的渗透系数得到了大量连续的圈闭气体饱和度及其准饱和渗透系数的数据。试验结果表明，在小于5%圈闭气体饱和度的区间，圈闭气体进入到无效孔隙中，因此不影响渗透系数的大小；圈闭气体饱和度在5%～6%时会形成孔喉阻塞效应，对渗透系数的影响加剧。在此基础上，构建了预测准饱和渗透系数的van Genuchten模型。与传统Faybishenko幂律模型相比，新构建的模型很好地表征了小圈闭气体饱和度对渗透系数影响不大的特征；在其他圈闭气体饱和度时，新模型与传统模型的预测性能相当。新构建的准饱和渗透系数模型为深入研究准饱和水流和溶质运移奠定了基础。
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关键词:
- 准饱和细砂介质 /
- 圈闭气体饱和度 /
- 渗透系数 /
- van Genuchten模型 /
- Faybishenko幂律模型
Abstract:The hydraulic conductivity of a quasi-saturated aquifer decreases with the increase of air-trapped saturation, but it is difficult to obtain a continuous data on air-trapped saturation through the traditional displacement experiments due to limitations in experimental operations and measurement accuracy. It limits the accurate characterization of the relationship between small air-trapped saturation and the corresponding quasi-saturated hydraulic conductivity. This study designed an oxygen-trapped dissolution experiment in quasi-saturated fine sands media, instead of air-trapped, in which the soluble oxygen in water and the corresponding hydraulic conductivity can be accurately measured. Then a large amount of continuous data on air-trapped saturation and its quasi-saturated hydraulic conductivity were obtained. The experimental results show that when the air-trapped saturation is less than 5%, trapped gas may enter the ineffective pores and thus has a little effect on the value of the hydraulic conductivity. However, when the trapped gas saturation is between 5%－6%, it forms a pore throat block effect, which intensifies the influence on the hydraulic conductivity. Furthermore, a new model, i.e., van Genuchten model, was constructed to predict the quasi-saturated hydraulic conductivity. This model overcomes the shortcomings of the traditional power-law model and well characterized the feature that the small air-trapped saturation has little effect on the hydraulic conductivity. At high air-trapped saturation, the performance of van Genuchten model is comparable to the traditional model. The proposed model in this study can provide foundation for studying quasi-saturated water flow and solute transport.
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