NDLI: Hydromechanical behavior during constant-rate pumping tests in fractured gneiss

Content Provider	Springer Nature Link
Author	Schweisinger, Todd Svenson, Erik J. Murdoch, Lawrence C.
Copyright Year	2011
Abstract	Deformation and fluid pressure during constant-rate pumping tests were characterized by sensitivity analyses using a theoretical model of a deformable fracture, and by conducting and analyzing field tests at a site underlain by fractured biotite gneiss in western South Carolina, USA. The sensitivity analysis indicates that displacement is a hysteretic function of fluid pressure during constant-rate pumping tests, and the signals are affected by properties of the fracture (normal stiffness, aperture, and heterogeneities in the fracture plane) and enveloping rock (elastic modulus and permeability). The field tests used a removable borehole extensometer to measure axial displacements in the pumping well. The field results are generally similar to simulations, and the hydraulic and mechanical properties obtained by inversion of the pumping test results are essentially the same as results from hydromechanical slug tests. The observed displacements early in the pumping tests are less than, whereas late in the test they are greater than predicted values assuming a uniform fracture. This difference can be explained as a consequence of preferential flow within the fracture. These results indicate that displacements in a wellbore are sensitive to details of fracture connectivity and preferential flow that are difficult to detect through the pressure signal alone.La déformation et la pression de fluide lors de pompages d’essai à débit constant ont été caractérisées par des analyses de sensibilité en utilisant un modèle théorique de fracture déformable et en réalisant et interprétant des essais de terrain sur un site de gneiss à biotite fracturé de l’ouest de la Caroline du Sud, Etats-Unis. L’analyse de sensibilité indique que le déplacement est une fonction hystérésis de la pression du fluide pendant les pompages d’essai à débit constant et que les signaux sont influencés par les propriétés de la fracture (rigidité normale, ouverture et hétérogénéités dans le plan de fracture) et par celles de la roche encaissante (module d’élasticité et perméabilité). Les essais sur le terrain ont utilisé un extensomètre de forage amovible pour mesurer les déplacements axiaux dans le puits de pompage. Les résultats de terrain sont généralement similaires aux simulations et les propriétés hydrauliques et mécaniques obtenues par inversion des résultats des pompages d’essai sont essentiellement les mêmes que les résultats des slug-tests. Les déplacements observés au début des pompages d’essai sont inférieurs aux valeurs prédites en supposant une fracture uniforme alors qu’à la fin des essais ils sont plus importants. Cette différence peut être expliquée par la conséquence d’écoulements préférentiels au sein de la fracture. Ces résultats indiquent que les déplacements dans un forage sont sensibles aux détails de la connectivité de la fracture et aux écoulements préférentiels qui sont difficiles à détecter par le seul signal de pression.Se caracterizaron la deformación y presión del fluido durante los ensayos de bombeo a caudal constante mediante un análisis de sensitividad usando un modelo teórico de fractura deformable, y llevando a cabo y analizando ensayos de campo en un sitio cuya base está constituida por un gneiss biotítico fracturado en el oeste de South Carolina, EEUU. El análisis de sensitividad indica que el desplazamiento es una función de histéresis de la presión del fluido durante los ensayos de bombeo a caudal constante, y que las señales están afectadas por propiedades de las facturas (rigidez normal, apertura y heterogeneidades en el plano de fractura) y de la roca envolvente (módulo de elasticidad y permeabilidad). Los ensayos de campo usaron un extensómetro extraíble de la perforación para medir el desplazamiento axial en el pozo de bombeo. Los resultados de campo son generalmente similares a las simulaciones, y las propiedades hidráulicas y mecánicas obtenidas por la inversión de los resultados de los ensayos de bombeo son esencialmente las mismas que los resultados a partir de ensayos slug. Los desplazamientos observados tempranamente en los ensayos de bombeo son menores que los valores predichos asumiendo una fractura uniforme, mientras que cuando el ensayo está en la etapa final son mayores. Esta diferencia puede ser explicada como una consecuencia del flujo preferencial dentro de la fractura. Estos resultados indican que los desplazamientos en un pozo son sensibles a los detalles de la conectividad de la fractura y al flujo preferencial que son difíciles para detectar a través de la solamente las señales de la presión.Foram efetuadas análises de sensibilidade da deformação e da pressão do fluido durante a realização de ensaios a caudal constante, através do uso de modelos teóricos de uma fratura deformável, e pela execução e interpretação de ensaios de caudal num local geologicamente constituído por gnaisses biotíticos fraturados, no oeste da Carolina do Sul, EUA. As análises de sensibilidade indicam que o deslocamento é uma função histerese da pressão do fluido durante ensaios a caudal constante, e que os sinais são afetados pelas propriedades da fratura (rigidez, abertura e heterogeneidades no plano de fratura) e da rocha envolvente (módulo de elasticidade e permeabilidade). Os ensaios de caudal usaram um extensómetro de poço removível para medir o deslocamento axial na captação em bombeamento. Os resultados de campo são geralmente similares às simulações, e as propriedades hidráulicas e mecânicas obtidas por inversão dos resultados do ensaio de caudal são essencialmente idênticos aos resultados dos slug tests. Os deslocamentos observados no início dos ensaios de caudal são menores, enquanto, mais tardiamente no ensaio, são maiores que os valores esperados, assumindo uma fratura uniforme. Esta diferença pode ser explicada como consequência do fluxo preferencial dentro da fratura. Os resultados indicam que os deslocamentos num furo de captação são sensíveis a pormenores como a conectividade das fraturas e a direcção preferencial de fluxo, as quais são difíceis de detetar apenas pela pressão do sinal.
Starting Page	963
Ending Page	980
Page Count	18
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	19
Issue Number	5
e-ISSN	14350157
Language	Portuguese
Publisher	Springer-Verlag
Publisher Date	2011-05-04
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Crystalline rock Fractured rock Inverse modeling Hydraulic testing USA Hydrogeology Waste Water Technology Water Pollution Control Water Management Aquatic Pollution Geology
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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