Development of spatial permeability variations in English Chalk aquifers
Development of spatial permeability variations in English Chalk aquifers
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英国白垩含水层空间渗透率变化的发展
DOI：
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
A. Foley
中科院分区：
文献类型：
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作者：
S. Worthington;A. Foley
英国白垩纪白垩岩形成双孔隙含水层，具有低渗透性基质和高渗透性裂缝网络，主要是由于溶解而扩大的应力释放裂缝。这种扩大是沿裂缝沿着通过的水的体积（流量效应）及其化学欠饱和度的函数。反馈效应导致了一个独特的渗透性结构的发展，有四个特殊的特点：（一）槽在地下水位与高transmittance和收敛的地下水流;（二）大幅增加transmissivities在一个downgradient方向;（三）downgradient降低水力梯度;和（四）从高transmittance区排放到表面通常在大量的弹簧。这种独特的自组织渗透结构发生在整个无压白垩含水层。在地下水位以下50-100米深处，裂缝的早期扩大是缓慢的，但由于非线性溶解动力学，接近地下水位和最上层基岩的裂缝扩大要快得多。模拟的溶解剖面显示，超过95%的溶解发生在基岩的顶部1米处，饱和区的裂缝扩大是由于在一百万年或更长的时间内发生的渐进溶解。
The Cretaceous Chalk in England forms dual-porosity aquifers, with low-permeability matrix and high-permeability networks of fissures, which are predominantly stress-relief fractures that have been enlarged by dissolution. This enlargement is a function of the volume of water that has passed along a fracture (the flowrate effect) and its degree of chemical undersaturation. Feedback effects result in the development of a distinctive permeability structure, with four particular characteristics: (i) troughs in the water table with high transmissivity and convergent groundwater flow; (ii) substantial increases in transmissivities in a downgradient direction; (iii) downgradient decreases in hydraulic gradient; and (iv) discharge from the high-transmissivity zones to the surface commonly at substantial springs. This distinctive self-organized permeability structure occurs throughout unconfined chalk aquifers. Early enlargement of fissures at a depth of 50–100 m below the water table is slow, but is much more rapid close to the water table and in the uppermost bedrock due to non-linear dissolution kinetics. A modelled dissolution profile shows that more than 95% of dissolution takes place in the top 1 m of bedrock, and that enlargement of fissures in the saturated zone results from progressive dissolution occurring over a period of a million years or more.