埔里盆地透水性垂向分佈量測

Measurement of Hydraulic Conductivity Along the Vertical Direction in the Puli Basin

陳柏瑞(Po-Jui Chen)

指導教授 ： 賈儀平

國立臺灣大學/理學院/地質科學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.00384

摘要

地層的透水性為地下水文研究與工程應用的重要參數，雖然透過抽水試驗可以量測含水層的平均水力傳導係數，但是無法得知其透水性的變化；而雙封塞微水試驗的方法操作不易，而且精確度欠佳。本研究利用熱脈衝流速儀在井孔內量測地層垂直方向透水性的變化，以得知含水層透水性於垂直方向之變化。

由於井徑大小不同以及抽水量的差異會造成流速儀量測上產生誤差，因此必須針對所記錄的資料進行校正。當流體的雷諾數值大於2100 時，水流會進入亂流的狀態，流體除了向前流動外，並碎成許多漩渦，這使得熱脈衝流速儀量測結果會產生大於實際的現象；受到流速儀之幾何形狀與自然對流等因素的影響，必須透過校正式來修正量測結果，根據測量井之井徑大小不同，其校正公式也有會所差異。

本研究的試驗地點共有兩口井徑直徑皆為8 吋的地下水監測井，兩口深度不同的井分別反應第一與第二含水層之水位變化。先將抽水機置入井內上方進行定量抽水，在井管內產生穩定之向上水流，再把熱脈衝流速儀放置在兩口井內進行垂直流速的量測，並且隨深度記錄地層透水性的變化。經過資料校正之後，原本抽水造成亂流的誤差得以修正，與地層柱以及自然伽瑪資料比對後結果良好，配合中央地質調查所的抽水試驗資料，推算出當地地層垂直方向連續性的水力傳導系數變化。結果顯示，第一含水層主要的透水區段為地下15.50 公尺處附近，而第二含水層主要的透水區段為地下40.75 公尺，雖然含水層的岩性變化不大，但是透水區段的水力傳導係數可達整體含水層之平均水力傳導係數的4.5 倍之高。

關鍵字

熱脈衝流速儀 ； 水力傳導係數 ； 含水層

並列摘要

The permeability of the layer is an important parameter for groundwater research and engineering application. Although one can use pumping-test to measure average hydraulic conductivity of aquifer, one cannot obtain the permeability changes of layers. However, it is difficult to operate double packer slug test and this test is lack of accuracy. The research is measuring the permeability changes of layers on the vertical direction inside the boreholes through heat-pulse flowmeter, therefore we could obtain the data for the permeability of the aquifer changes on the vertical direction.
Due to the difference of well diameters and the amount of pump water, it will cause error when measuring through flowmeter. When Reynolds number of the fluid is bigger than 2100, the flow will enter the turbulent flow status; the fluid will be not only moving forward, but also breaking into eddies and causes the measurement result larger than the reality. Measurement result is affected by the geometric shapes of flowmeter and natural convections, we have to leverage calibration formulas to adjust the measurement results. The calibration formulas would vary by different sizes of well diameters.
The study has been conducted with two wells with diameter as 8 inches but different depths to reflect the water level changes of first and second aquifer. We first pumped water at the top of the well and generated a stable upward flow, and then used heat-pulse flowmeter to measure the flow speed on the vertical direction for the two wells. We recorded the permeability of the layer changes as the depth changed. By using the calibration formula, we could correct the error caused by the turbulent flow when pumping. This has been compared with the stratigraphic column and natural gama and showed great result. Leveraging pumping water data from Central Geological Survey MOEA, we could calculate its continuous changes of hydraulic conductivity on the vertical direction. The result showed that major high permeability section of first aquifer is around below 15.50 meter and the major high permeability of second aquifer is around below 40.75 meter. Although the lithology changes of aquifer is not significant, the hydraulic conductivity of high permeability sections could be as high as 4.5 times of the average hydraulic conductivity of overall aquifer.

並列關鍵字

Heat-pulse Flowmeter ； Hydraulic Conductivity ； Aquifer

參考文獻

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