大傾角裂隙岩層抽水試驗用雙孔隙率模式分析;A Double-Porosity Model for Pumping Test in a Fractured Formation with a Large Dipping Angle

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题名:	大傾角裂隙岩層抽水試驗用雙孔隙率模式分析;A Double-Porosity Model for Pumping Test in a Fractured Formation with a Large Dipping Angle
作者:	吳繹平;Wu,Hyi-ping
贡献者:	應用地質研究所
关键词:	雙孔隙率模式;抽水試驗;大傾角;Double-Porosity Model;Pumping test;Dipping angle
日期:	2015-01-19
上传时间:	2015-03-16 16:06:47 (UTC+8)
出版者:	國立中央大學
摘要:	新竹尖石裂隙含水層場址之井孔攝影顯示裂隙帶的傾角分布範圍從30度至60度。如此大的傾角會產生區域性水流，在裂隙帶中抽水試驗產生一非徑向流場；抽水井上、下游地下水壓力變化不一致，且會形成類似捕集區的效應。目前所有的抽水試驗模式中，均假設地層為水平，本研究想了解裂隙傾角對抽水試驗的影響，藉由進行雙封塞抽水試驗與建立具傾角影響之雙孔隙率模式來達成此目的。模式中雙孔隙率的部份採用集總參數的方法來模擬岩體母質與裂隙之間的水流互補機制。在新的模式中，透過經驗參數可預測裂隙傾角影響的極限值，小於此極限值的裂隙傾角可忽略，進行現地資料分析時直接使用水平裂隙模式即可，反之，需考慮傾角影響的情況下，抽水井、觀測井與裂隙之間的方位也需納入考量；模擬抽水試驗時，裂隙帶走向、抽水井與觀測井之間的位置若趨近於平行，與水平模式相比較，水平模式求得裂隙帶 Kf 值比具傾角影響的模式求得 Kf 值高估100倍左右，若趨近於正交方向時，則會高估10至20倍左右；此外，裂隙的傾角不會影響集總參數，因為裂隙中的壓力水頭依然為徑向分布，上下游分布不均為均勻流帶來的影響所致。本研究於103年1月3日至6日在新竹尖石裂隙含水層場址進行25小時的雙封塞抽水試驗，抽水率為每分鐘40公升，含水層的裂隙帶大致上由北向南傾30度，厚度為0.5米，觀測井位於抽水井東側5米，將現地資料帶入模式後亦得到理論分析的結果，本研究認為，在分析抽水試驗時，確實有必要考慮裂隙傾角產生的影響。;At the research well field of National Central University, the borehole camera images indict that the dip angle of the fractured zone can be as large as 30-60 degree. Such a large dip angle causes a regional flow in the fractured zone and renders the flow field of a pumping test to be radially asymmetric, where the pressure response in the down-gradient and up-gradient of the pumping well is different and a capture zone effect exists in the neighborhood of the pumping well. All the well hydraulics models currently available neglect the dip angle effect. To incorporate the dip angle effect, this project develops a new double-porosity pumping test model, where the matrix flow between the rock matrix and the fractured zone is modeled using the lumped-parameter approach. In the new model, according to the empirical parameters which can be used to predict the limit of the dip angle effect. The dip angle effect is negligible if the dip angle is less than the limit, the field data analysis can using the horizontal fracture model. Otherwise, in the effective situation, the position of the pumping well, observation well and fracture formation strike also need to be considered in. When modeling the pumping test, if observation well and pumping well that are located along the dip angle direction, the horizontal fracture model result of the hydraulic conductivity of the fracture K_f is larger 100 times than the dip angle effect fracture model. If observation well and pumping well that are located along the direction about orthogonal to the dip angle, then the K_f will larger 10-20 times than the dip angle effect fracture model. In addition, the dip angle does not affect the lumped parameter because the pressure head of the fractured zone is radial distribution, both upstream and downstream distribution is effect by the uniform flow only. A 25-hour constant-rate pumping test (40 l/ min) had been conducted from 2014/01/03 to 01/06 in the research well field. The dip angle is 30 degree for the fractured zone, running north to south. The thickness of the fracture zone is about 0.5 meters. The observation well locates about 5 meters from the pumping well. The field data analysis also confirms the theoretical analysis results of the dip angle effect. In this project, we think the dip angle is needed to consider during the pumping test.
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