Analytical Interpretation of Slug Test in a Vertical Cutoff Wall

An analysis method for slug tests performed in a partially penetrating well within a vertical cutoff wall is presented. A steady‐state shape factor for evaluating hydraulic conductivity of the material within the wall was derived by applying the method of images to the previously developed analytical solution of Zlotnik et al. (2010) for an infinite aquifer. Two distinct boundary conditions were considered: constant‐head boundary for the case of direct contact between the wall and the aquifer, and no‐flux boundary representing an impermeable filter cake on the sides of the wall. The constant‐head and no‐flux boundary conditions yield significantly higher and lower shape factors, respectively, than those for the infinite aquifer. Consequently the conventional line‐fitting method for slug test analysis would yield an inaccurate estimate of the hydraulic conductivity of a vertical cutoff wall.     

A Program to Calculate Hydraulic Conductivity Using Slug Test Data

Abstract. During the execution of a slug test, the water level in a well is instantaneously raised or lowered and changes in the water level are monitored as it seeks its equilibrium position. SLUGTST is a program, written in TURBO BASIC ^b for IBM PC ^c microcomputers and compatibles, which calculates hydraulic conductivity using data obtained during such a test.     

An Assessment of the Nguyen and Finder Method for Slug Test Analysis

The Nguyen and Pinder method is one of four techniques commonly used for analysis of response data from slug tests. Limited field research has raised questions about the reliability of the parameter estimates obtained with this method. A theoretical evaluation of this technique reveals that errors were made in the derivation of the analytical solution upon which the technique is based. Simulation and field examples show that the errors result in parameter estimates that can differ from actual values by orders of magnitude. These findings indicate that the Nguyen and Pinder method should no longer be a tool in the repertoire of the field hydrogeologist. If data from a slug test performed in a partially penetrating well in a confined aquifer need to be analyzed, recent work has shown that the Hvorslev method is the best alternative among the commonly used techniques.     

SlugIn 1.0: A Free Tool for Automated Slug Test Analysis

The correct characterization of aquifer parameters is essential for water‐supply and water‐quality investigations. Slug tests are widely used for these purposes. While free software is available to interpret slug tests, some codes are not user‐friendly, or do not include a wide range of methods to interpret the results, or do not include automatic, inverse solutions to the test data. The private sector has also generated several good programs to interpret slug test data, but they are not free of charge. The computer program SlugIn 1.0 is available online for free download, and is demonstrated to aid in the analysis of slug tests to estimate hydraulic parameters. The program provides an easy‐to‐use Graphical User Interface. SlugIn 1.0 incorporates automated parameter estimation and facilitates the visualization of several interpretations of the same test. It incorporates solutions for confined and unconfined aquifers, partially penetrating wells, skin effects, shape factor, anisotropy, high hydraulic conductivity formations and the Mace test for large‐diameter wells. It is available in English and Spanish and can be downloaded from the web site of the Geological Survey of Spain. Two field examples are presented to illustrate how the software operates.     

A User Interface for the Kansas Geological Survey Slug Test Model

The Kansas Geological Survey (KGS) developed a semianalytical solution for slug tests that incorporates the effects of partial penetration, anisotropy, and the presence of variable conductivity well skins. The solution can simulate either confined or unconfined conditions. The original model, written in FORTRAN, has a text-based interface with rigid input requirements and limited output options. We re-created the main routine for the KGS model as a Visual Basic macro that runs in most versions of Microsoft Excel and built a simple-to-use Excel spreadsheet interface that automatically displays the graphical results of the test. A comparison of the output from the original FORTRAN code to that of the new Excel spreadsheet version for three cases produced identical results.     

A Novel Semi-Analytical Solution of Over-Damped Slug Test in a Three-Layered Aquifer System

The slug test has been commonly used to estimate aquifer parameters. Previous studies on the slug test mainly focused on a single-layer aquifer. However, understanding the interaction between layers is particularly important when assessing aquifer parameters under certain circumstances. In this study, a new semi-analytical model on transient flow in a three-layered aquifer system with a partially penetrating well was developed for the slug test. The proposed model was solved using the Laplace transform method and the Goldstein-Weber transform method, where the semi-analytical solution for the model was obtained. The drawdowns of the proposed model were analyzed to understand the impacts of the different parameters on the drawdowns in a three-layered aquifer system. The results indicated that groundwater interactions between the layers have a significant impact on the slug test. In addition, a shorter and deeper well screen as well as a greater permeability ratio between the layers creates a greater interface flow between them, leading to a higher drawdown in the slug test. Finally, a slug test in a three-layered aquifer system was conducted in our laboratory to validate the new model, which indicated that the proposed model performed better in the interpretation of the experimental data than a previous model proposed by Hyder et al. (1994). We also proposed an empirical relationship to qualitatively identify the errors in the application of single-layer model for the analysis of response data in a three-layered aquifer system.     

鄂尔多斯盆地南部黄土塬区地震资料处理与解释 第二部分:地震资料解释

鄂尔多斯盆地南部的黄土高原,由于长期 风化、侵蚀,形成了树枝状水系与沟、塬、梁、峁、 坡并存的独特黄土地貌。针对这种复杂地表条件长 庆物探已建立了沿沟弯线为主、辅以黄土塬多线和 网状三维的采集方法;确立了高精度静校正、适度 去噪、共反射面元优化及已知井反射系数序列控制 的高保真处理方法、本文着重介绍处理、解释二大 环节的关键方法及应用效果。     

Assessing the Hydraulic Conductivity Anisotropy and Skin-Effect Based on Data of Slug Tests in Partially Penetrating Wells

Water Resources - A semianalytic and approximate analytical solution is given to the problem of slug test in a partially penetrating well in a confined or unconfined anisotropic aquifer. An...     

2-D Versus 3-D Magnetotelluric Data Interpretation

In recent years, the number of publications dealing with the mathematical and physical 3-D aspects of the magnetotelluric method has increased drastically. However, field experiments on a grid are often impractical and surveys are frequently restricted to single or widely separated profiles. So, in many cases we find ourselves with the following question: is the applicability of the 2-D hypothesis valid to extract geoelectric and geological information from real 3-D environments? The aim of this paper is to explore a few instructive but general situations to understand the basics of a 2-D interpretation of 3-D magnetotelluric data and to determine which data subset (TE-mode or TM-mode) is best for obtaining the electrical conductivity distribution of the subsurface using 2-D techniques. A review of the mathematical and physical fundamentals of the electromagnetic fields generated by a simple 3-D structure allows us to prioritise the choice of modes in a 2-D interpretation of responses influenced by 3-D structures. This analysis is corroborated by numerical results from synthetic models and by real data acquired by other authors. One important result of this analysis is that the mode most unaffected by 3-D effects depends on the position of the 3-D structure with respect to the regional 2-D strike direction. When the 3-D body is normal to the regional strike, the TE-mode is affected mainly by galvanic effects, while the TM-mode is affected by galvanic and inductive effects. In this case, a 2-D interpretation of the TM-mode is prone to error. When the 3-D body is parallel to the regional 2-D strike the TE-mode is affected by galvanic and inductive effects and the TM-mode is affected mainly by galvanic effects, making it more suitable for 2-D interpretation. In general, a wise 2-D interpretation of 3-D magnetotelluric data can be a guide to a reasonable geological interpretation.     

Processing And Interpretation Of Electromagnetic Induction Array Data

The simultaneous nature of array data can be exploitedin electromagnetic induction studiesfor three general purposes.First, one or more reference sites can be usedto reduce bias, improve signal-to-noise ratios, and provide bettercontrol over source complications and coherent noisein estimates of MT impedances and otherEM transfer functions (TFs).Although a single good reference site can dramatically improveTF estimates, improvements due to multiple sites are often rather modest, because local noise is the limiting factor.Secondly, arrays allow for estimation of inter-station transfer functions, and maps of anomalous horizontal field variations. Relatively straightforward modifications to inversion codes wouldallow quantitative interpretation of these additionalconstraints on resistivity variations.Finally, with arrays it is possible to estimate the response of theEarth to a richer spectrum of external source excitations. In particular,the natural extension to the usual uniform source assumption implicit inthe MT method allows for three curl-free magnetic gradient sources.Quantitative interpretation of the response of a three-dimensionalEarth to these sources could provide additionalconstraints on large scale variations in crustal and uppermantle resistivity, and might help to overcome problemsdue to aliasing of near surface distortion in widely spaced MT data.