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Hydrogeology Journal

, Volume 17, Issue 3, pp 589–600 | Cite as

Understanding diagnostic plots for well-test interpretation

  • Philippe RenardEmail author
  • Damian Glenz
  • Miguel Mejias
Report

Abstract

In well-test analysis, a diagnostic plot is a scatter plot of both drawdown and its logarithmic derivative versus time. It is usually plotted in log–log scale. The main advantages and limitations of the method are reviewed with the help of three hydrogeological field examples. Guidelines are provided for the selection of an appropriate conceptual model from a qualitative analysis of the log-derivative. It is shown how the noise on the drawdown measurements is amplified by the calculation of the derivative and it is proposed to sample the signal in order to minimize this effect. When the discharge rates are varying, or when recovery data have to be interpreted, the diagnostic plot can be used, provided that the data are pre-processed by a deconvolution technique. The effect of time shift errors is also discussed. All these examples show that diagnostic plots have some limitations but they are extremely helpful because they provide a unified approach for well-test interpretation and are applicable in a wide range of situations.

Keywords

Hydraulic testing Conceptual models Hydraulic properties Analytical solutions 

Comprendre l’utilisation des graphes de diagnostic pour l’interprétation des essais de pompage

Résumé

Dans le domaine de l’interprétation des essais de pompage, un graphe de diagnostic est un graphe simultané du rabattement et de sa dérivée logarithmique en fonction du temps. Ce graphe est habituellement représenté en échelle bi-logarithmique. Les avantages principaux et les limites de cet outil sont discutés à l’aide de trois exemples hydrogéologiques réels. Des recommandations pratiques sont proposées afin d’utiliser ces graphes pour sélectionner un modèle conceptuel d’écoulement. Lorsque les mesures de rabattement sont bruitées, le calcul de la dérivée logarithmique présente des artefacts que l’on peut minimiser en échantillonnant le signal. Lorsque le débit de pompage varie, ou lors d’un test de récupération, les graphes de diagnostic peuvent aussi être utilisé à condition d’effectuer une déconvolution des données au préalable. Enfin, les effets d’une erreur d’estimation du temps de début d’un test sont discutés. Tous ces exemples montrent que les graphes de diagnostic constituent un outil extrêmement utile pour l’interprétation des essais hydrauliques.

Comprensión de gráficos diagnósticos para la interpretación de ensayos de pozos

Resumen

En los análisis de ensayos de pozos, un gráfico de diagnóstico es un gráfico de dispersión de las depresiones y de sus derivadas logarítmica en función del tiempo. Usualmente se grafica en una escala log – log. Las principales ventajas y limitaciones del método se revisaron con la ayuda de tres ejemplos hidrogeológicos de campo. Se proveen pautas para la selección de un modelo conceptual apropiado a partir de un análisis cualitativo de la derivada logarítmica. Se muestra cómo el ruido en las mediciones de las depresiones resulta amplificado por el cálculo de las derivadas y se propone muestrear la señal con el objeto de minimizar este efecto. Cuando los ritmos de descarga varían, o cuando los datos de recuperación deben ser interpretados, el gráfico diagnóstico puede ser utilizado siempre que los datos sean pre-procesados por una técnica de deconvolución. Asimismo se discute el efecto de los errores de desplazamiento del tiempo. Todos estos ejemplos muestran que el gráfico diagnóstico tiene algunas limitaciones pero son extremadamente útiles porque proveen un enfoque unificado para la interpretación de ensayos de pozos y son aplicables en una amplia gama de situaciones.

理解用于解释抽水试验结果的诊断图

摘要

在抽水试验分析中, 诊断图是降深及其对数导数与时间之间的关系的散点图. 经常绘于双对数坐标中. 通过三个水文地质野外实例评述了该方法的主要优点和局限. 提出了通过对数导数的定性分析选择合适概念模型的原则. 说明了降深测量的噪声在导数计算中是如何被放大的, 并建议对信号进行采样以减小这种影响. 当抽水量变化或需要解释水位恢复数据时, 在对数据进行反卷积手段预处理后, 可应用诊断图. 此外, 还讨论了时移误差的影响. 这些实例都表明, 诊断图有一定的局限性, 但非常有用, 因为它们为抽水试验的解释提供了一种统一的方法, 并且适用于很多情形.

Compreensão de gráficos diagnóstico para interpretação de ensaios de caudal em furos

Resumo

Na análise de ensaios de caudal em furos, um gráfico diagnóstico é um diagrama de dispersão do rebaixamento e da sua derivada logarítmica em função do tempo. A projecção é usualmente feita em escala log–log. As principais vantagens e limitações do método são revistas com a ajuda de três exemplos hidrogeológicos de campo. São fornecidas orientações para a selecção de um modelo conceptual apropriado, a partir da análise qualitativa da derivada logarítmica. É mostrado como o ruído nas medições do rebaixamento é amplificado pelo cálculo da derivada e é proposto como amostrar o sinal para minimizar esse efeito. Quando os caudais variam, ou quando os dados de recuperação têm que ser interpretados, o gráfico diagnóstico pode ser usado desde que os dados sejam pré-processados por uma técnica de desconvolução. Também é discutido o efeito dos erros de desvio de tempo. Todos estes exemplos mostram que os gráficos diagnóstico têm algumas limitações mas são extremamente úteis porque dão uma aproximação unificada à interpretação de ensaios de caudal e são aplicáveis numa grande variedade de situações.

Comprendere l’utilizzo dei grafici diagnostici per l’interpretazione di prove di pompaggio

Riassunto

Nel dominio dell’interpretazione delle prove di pompaggio, un grafico diagnostico è un grafico simultaneo dell’abbassamento e della sua derivata logaritmica in funzione del tempo. Questo grafico è solitamente rappresentato in scala bi-logaritmica. I principali vantaggi ed i limiti di questo strumento sono discussi attraverso tre esempi idrogeologici reali. Delle raccomandazioni pratiche sono proposte al fine di utilizzare questi grafici per scegliere un modello concettuale di flusso. Quando le misure di abbassamento contengono del rumore, il calcolo della derivata logaritmica presenta degli artefatti che sono riducibili campionando il segnale. Quando la portata del pompaggio varia, o durante un test di recupero, i grafici diagnostici possono anche essere utilizzati a condizione di effettuare una preliminare deconvoluzione dei dati. Infine, gli effetti di un errore di stima del tempo di inizio di un test sono discussi. Tutti gli esempi mostrano che i grafici di diagnosi costituiscono uno strumento estremamente utile per l’interpretazione delle prove idrauliche.

Notes

Acknowledgements

The authors thank R. Beauheim, P. Hsieh and an anonymous reviewer for their constructive comments which helped to improve the manuscript. The work was conducted within a joint research project funded by the Geological Survey of Spain and the University of Neuchâtel. Philippe Renard was supported by the Swiss National Science Foundation (grant PP002–1065557).

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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  1. 1.Centre for HydrogeologyUniversity of NeuchâtelNeuchâtelSwitzerland
  2. 2.Geological Survey of Spain (IGME)MadridSpain

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