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Hydrogeology Journal

, 17:1805 | Cite as

Estimating specific yield and transmissivity with magnetic resonance sounding in an unconfined sandstone aquifer (Niger)

  • M. Boucher
  • G. Favreau
  • J. M. Vouillamoz
  • Y. Nazoumou
  • A. Legchenko
Technical Note

Abstract

The unconfined aquifer of the Continental Terminal in Niger was investigated by magnetic resonance sounding (MRS) and by 14 pumping tests in order to improve calibration of MRS outputs at field scale. The reliability of the standard relationship used for estimating aquifer transmissivity by MRS was checked; it was found that the parametric factor can be estimated with an uncertainty ≤150% by a single point of calibration. The MRS water content (θ MRS) was shown to be positively correlated with the specific yield (Sy), and θ MRS always displayed higher values than Sy. A conceptual model was subsequently developed, based on estimated changes of the total porosity, Sy, and the specific retention Sr as a function of the median grain size. The resulting relationship between θ MRS and Sy showed a reasonably good fit with the experimental dataset, considering the inherent heterogeneity of the aquifer matrix (residual error is ∼60%). Interpreted in terms of aquifer parameters, MRS data suggest a log-normal distribution of the permeability and a one-sided Gaussian distribution of Sy. These results demonstrate the efficiency of the MRS method for fast and low-cost prospection of hydraulic parameters for large unconfined aquifers.

Keywords

Magnetic resonance sounding (MRS) Pumping test Hydraulic properties Sedimentary rocks Niger 

Estimation par résonance magnétique des protons de la porosité de drainage et de la transmissivité d'un aquifère libre gréseux (Niger)

Résumé

L’aquifère libre du Continental terminal du Niger a été reconnu par sondage résonance magnétique (MRS) et par 14 tests de pompage afin d’améliorer la calibration du signal MRS à l’échelle du terrain. La validité de la relation standard utilisée pour estimer la transmissivité d’un aquifère par MRS a été vérifiée; on a trouvé par simple calibration que le facteur paramétré peut être estimé avec une incertitude ≤150%. On a montré par six tests de pompage que la teneur en eau MRS (θ MRS) était corrélée positivement à la productivité (Sy), et que les valeurs de (θ MRS) étaient toujours supérieures à (Sy). Un modèle conceptuel a par suite été développé, basé sur les variations de la porosité totale Sy et sur la capacité de retention, en fonction de la granulométrie moyenne. La relation établie entre (θ MRS) et Sy donne des résultats en cohérence relativement bonne avec l’ensemble des données expérimentales si l’on considère l’hétérogénéité de l’aquifère (erreur résiduelle ×60%). Interprétées en termes de paramètres de l’aquifère, les données MRS suggèrent une distribution log-normale de la perméabilité et une distribution gaussienne à une branche des Sy. Ces résultats montrent l’efficacité de la méthode RMS pour l’évaluation rapide et à bas coût des paramètres hydrauliques des grands aquifères libres.

Estimación de la capacidad de almacenamiento y transmividad con prospección de resonancia magnética en un acuífero no confinado de areniscas (Niger)

Resumen

Se investigó el acuífero no confinado del Continental Terminal en Niger mediante prospección de resonancia magnética (MRS) y a través de 14 ensayos de bombeo con el objeto de mejorar la calibración de las salidas de MRS a escala de campo. Se chequeó la confiabilidad de las relaciones standards usadas para estimar la transmisividad del acuífero por MRS; se encontró que el factor paramétrico puede ser estimado con una incerteza de ≤150% por un solo punto de calibración. Se demuestra que el contenido de agua MRS (θ MRS) está positivamente correlacionado con el coeficiente de almacenamiento (Sy), estimado por seis ensayos de bombeo, y θ MRS siempre exhibió valores mayores que Sy. Se desarrolló posteriormente un modelo conceptual, basado en los cambios estimados de la porosidad total, Sy, y la retención específica Sr en función del tamaño de grano medio. La relación resultante entre θ MRS y Sy mostró un ajuste razonablemente bueno con el conjunto de datos experimentales, considerando la heterogeneidad inherente de la matriz del acuífero (el error residual es ×60%). Interpretado en términos de parámetros del acuífero, los datos MRS sugieren una distribución log- normal de la permeabilidad y una distribución Gaussiana sesgada de Sy. Estos resultados demuestran la eficiencia del método de MRS para una prospección rápida y de bajo costo de los parámetros hidráulicos en grandes acuíferos no confinados.

Estimação do armazenamento específico e da transmissividade através de prospecção com ressonância magnética aplicada a um aquífero arenoso livre (Níger)

Resumo

O aquífero livre do Terminal Continental, no Níger, foi investigado através de prospecção com ressonância magnética (RM) e 14 ensaios de bombagem, de modo a melhorar a calibração dos resultados da RM à escala de campo. A fiabilidade da relação standard que se usa para estimar a transmissividade de um aquífero através da RM foi analisada; verificou-se que o factor paramétrico pode ser estimado com uma incerteza ≤150%, com um único ponto de calibração. O conteúdo de água obtido na RM (θ RM) apresenta uma correlação positiva com o armazenamento específico (Ss), estimado através de seis ensaios de bombagem, e o θ RM apresentou sempre valores mais elevados que o Ss. Seguidamente foi desenvolvido um modelo conceptual baseado nas modificações estimadas para a porosidade total, Ss, e retenção específica, Sr, em função da dimensão mediana dos clastos. A relação resultante entre o θ RM e o Ss mostrou uma concordância relativamente boa com os resultados experimentais, tendo em conta a heterogeneidade inerente da matriz do aquífero (erro residual de aproximadamente 60%). Em termos de parâmetros do aquífero, os dados de RM sugerem uma distribuição log-normal da permeabilidade e uma distribuição Gaussiana do tipo one-side do Ss. Estes resultados demonstram a eficiência do método de RM para prospecção, rápida e de baixo custo, dos parâmetros hidráulicos de aquíferos livres de grandes dimensões.

应用核磁共振测深技术估算砂岩潜水含水层的给水度和导水系数(尼日尔)

摘要:

应用核磁共振测深技术(MRS)对位于尼日尔Continental Terminal的潜水含水层进行了调查, 并利用14个抽水试验来改善对场地尺度MRS输出的校正。对用MRS估算含水层导水系数的标准关系的可靠性进行了检验; 结果表明, 单点校验的参数因子估算值误差≤150%。六个抽水试验结果显示, MRS含水率(θMRS)与给水度(Sy)呈正相关, 并且θMRS总是高于Sy。随后根据估算的随粒径中值变化的总孔隙度、Sy和持水度Sr的改变量, 建立了概念模型。考虑到含水层介质内部的非均匀性(残差为60%), 所得到的θMRS与Sy之间的关系同实验数据吻合很好。MRS数据在转化为含水层参数后表明, 渗透率呈对数正态分布, Sy呈单侧高斯分布。这些结果证实, MRS方法是大规模潜水层快速、低成本的水力参数勘探的有效方法。

Notes

Acknowledgements

This work was partially funded by the AMMA project. Based on a French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, especially from France, the UK, the US and Africa. It has been the beneficiary of a major financial contribution from the European Community’s Sixth Framework Research Programme. Detailed information on scientific coordination and funding is available on the AMMA International website http://www.amma-international.org. Borehole data were made available thanks to the library of the Ministry of Hydraulics in Niamey, Niger. The authors warmly acknowledge IRD staff in Niger for their efficient involvement in field work.

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • M. Boucher
    • 1
    • 2
  • G. Favreau
    • 3
    • 4
  • J. M. Vouillamoz
    • 5
  • Y. Nazoumou
    • 4
  • A. Legchenko
    • 6
  1. 1.CNRS, UMR HydroSciencesUniversité de Montpellier 2Montpellier cedex 5France
  2. 2.IRDUMR HydroSciencesNiameyNiger
  3. 3.IRD, UMR HydroSciencesUniversité de Montpellier 2Montpellier cedex 5France
  4. 4.Département de GéologieUniversité Abdou MoumouniNiameyNiger
  5. 5.IRD, UMR LTHE, Indo-French Cell for Water ScienceIndian Institute of ScienceBangaloreIndia
  6. 6.IRDUMR LTHEGrenoble cedex 9France

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