Prediction of flow rates for potable water supply from directionally drilled horizontal wells in river sediments

Abstract

Horizontal wells installed by directional drilling in the highly permeable river bottom sediments can improve the quality of water delivered to water treatments plants by filtration of suspended solids and dilution with groundwater. Predicting the flow rates available from horizontal wells is an important step in evaluating the technology. A series of three-dimensional finite element models were developed to simulate a horizontal well located beneath a river and a parametric analysis of predicted flow as a function of pipe length, pipe diameter, depth below river bottom, and sediment hydraulic conductivity was conducted to determine optimum horizontal well configurations. The results indicated that the frictional head losses in the well screen have a significant impact on predicted withdrawal rates. Analysis of well length and pipe diameter indicates that for each specific well configuration there exists an optimum length, beyond which little increase in flow occurs. The simulations indicated maximum flows occur when horizontal wells are placed as deep as possible until they are within 0.5 to 2.5 m of an impermeable lower boundary.Key words: directional drilling, water supply, horizontal wells, river filtration.