Analytically Supported Numerical Modeling of Horizontal and Radial Collector Wells

Abstract

Riverbank filtration (RBF) is widely used in drinking water production all over the world. The horizontal and radial collector wells are among the most important water production facilities in case of the RBF aquifers. In this study several types of modeling methods are used to analyze the hydraulic conditions of horizontal and radial collector wells. The unsteady and steady-state flow in homogeneous, infinite, semi-infinite, and square-shaped bounded aquifers are investigated. The effect of delayed gravity response is modeled. Three-dimensional analytical and numerical finite-difference (FD) solution techniques are applied during the simulations to provide more reliable calculation results. Comparative analyses are carried out to optimize the wellbore drawdown in FD simulations. This important value is controlled by the local head loss due to the radial flow in vertical plane normal to the axes of screens. The multimesh FD simulation software FLOW is used for infinite and semi-infinite aquifers, while the MODFLOW Revised Multi-Node Well (MNW2) package is applied to the square-shaped aquifers. The late time partitioning (LTP) method is introduced to estimate the late time drawdown in infinite aquifers using semianalytical steadystate drawdown equations considering circular recharge boundaries. The latter value is derived by the semianalytical CW software. The use of results of various mostly analytically based solutions confirmed or improved the accuracy of the approximate numerical solutions. Such analytical support is vital for proper evaluation of the operation of horizontal and radial collector wells.

Hydraulic testing of specialised water production structures (horizontal collector well) in riverbank filtration systems

“…In our previous works (Székely et al, 2021), the fact that the inflowing yield increases away from the well along the arms of the horizontal well has already been explained. This growth is exponential.…”

“…to subject the well to a nearly constant hydraulic load. In the case of HCWs, the volume of water entering the well along a given length of the arm is not constant but increases exponentially towards the end of the arm (Székely et al, 2021). This yield distribution is also influenced by the distance of the well from the river.…”

“…The application of the Revised Multi-Node Well (MNW2) package of MODFLOW allowed us to investigate the hydraulic conditions of HCWs. The MNW2 program was originally developed for the hydrodynamic modeling of horizontally drilled and horizontally formed wells but has been shown in previous studies to be suitable for the hydraulic simulation of horizontal collector wells (Nyiri et al, 2019;Székely et al, 2021). With this method, we aimed to determine the distribution of the total yield produced by the horizontal collector well among the arms and to determine the extent of depression in HCWs installed at different distances and its evolution.…”

Examination of the effect of the river in riverbank filtrated system using field measurements

“…In the case of riverbank filtered water bases, the so-called horizontal collector well is a water extraction artefact often used. This well type consists of three larger structural units: the superstructure, the large-diameter well shaft, and the filter pipes extending horizontally and radially from it, the so-called arms (Székely et al, 2021). Their advantage is that in the case of thin aquifer layers typical of riverbank filtration systems, the horizontal arm arrangement increases the effective filter surface compared to the filter surface of vertical wells.…”