双层抽水试验中观测井井筒效应的数值模拟研究

Numerical simulation study on wellbore effects of observation well in pumping test of double-aquifer

建立了具有代表性的双层含水层抽水概念模型,基于等效渗透系数法建立了井筒—含水层耦合数值模拟模型,利用该模型模拟了双层抽水试验中观测井井筒及周边水头降深的分布、观测井内部水流的垂向分布、含水层与观测井的补给关系。分析了井筒效应的发生机理及观测井井筒内径和径距对井筒效应的影响规律,得出以下主要结论:在双层含水层中利用不完整井抽水时,同一水平位置不同高度处的水头降深不一样,由此导致的垂直方向的水头差会导致观测井内产生垂向水流,水流的流量受观测井井径和径距影响,井径越大流量越大,径距越大流量越小;观测井中的垂向流量会导致井筒周边含水层水头的重分布,此即井筒效应。距离观测井越近,受井筒效应影响越大。同时井筒效应的影响程度和影响范围受观测井井径和径距决定,井径越大影响程度和范围越大,径距越大影响程度和范围越小。

It is focused on the influence of observation wellbore on the head distribution of its surrounding aquifer. To resolve this problem,an EHC method was introduced and a coupled wellbore-aquifer model was built. Employing this model,drawdown distribution in and around a wellbore,vertical flow within it and the recharge relationship between the observation well and its surrounding aquifer was simulated. In addition,the occurrence mechanism of wellbore effect,as well as the influence law of wellbore diameter and radial distance of observation well from the pumping well on wellbore effects was deeply analyzed. The main findings are：when pumping water from layered aquifer system,drawdown difference occurs in different height in the same horizon position,which then lead to the vertical flow in the wellbore of observation well. The rate of vertical flow are influenced by the diameter of the observation and its distance away from pumping well： the larger the diameter is and the smaller the distance is,the larger the flow rate is; vertical flow in the wellbore well cause the redistribution of head within and around the observation well,which can be named as wellbore effect. As the diameter increases and distance decreases,the range influenced by wellbore effect will be larger and theextent will increase.