Abstract
An integrated set of different measurements has been used to study the behavior of groundwater in an observation well in a fractured rock formation, the UK Chalk, under pumped and ambient conditions. Under pumped conditions, the response of the open borehole was relatively straightforward with flow mainly concentrated along four discrete flow horizons. Furthermore, excellent correspondence was observed between the three methods of borehole flow velocity measurement: impeller flowmeter, heat-pulse flowmeter and dilution testing. Under ambient conditions, the system appeared more complicated. Specifically, in the upper half of the borehole, the impeller flowmeter exhibited substantial downward flow and the heat-pulse flowmeter exhibited almost negligible upward flow, whilst dilution testing indicated significant dilution. It was concluded that this was due to cross-flow occurring over the upper 29 m. Analysis of drawdown data, recovery data and a Drost analysis of the ambient cross-flow data yielded aquifer transmissivity estimates of 2,049, 2,928 and > 4,388 m2/day respectively. The discrepancy between the drawdown and recovery estimates was attributed to non-linear head-losses associated with turbulence and inertial effects. The difference between the pumping test and Drost results was explained by the flow during the pumping test bypassing this aforementioned 29 m region of rock.
Résumé
Un ensemble de différentes mesures a été utilise afin d’étudier le comportement hydraulique de l’eau souterraine dans un piezometer d’une formation fissurée de la Craie du Royaume Uni, en conditions de sollicitation par pompage et en conditions naturelles. La réponse d’un des ouvrages en conditions de pompage était relativement directe avec un écoulement principalement concentré le long de quatre horizons spécifiques. De plus, les résultats obtenus à l’aide de trois méthodes de mesure des flux en forage sont cohérents : mesure du flux à hélices, mesure du flux par impulsion de chaleur et mesure par dilution. En conditions naturelles, le système apparaît plus compliqué. De manière plus spécifique, dans la moitié supérieure du forage, la mesure du flux à hélices indiquait des flux descendants, la mesure du flux par impulsion de chaleur des flux ascendants négligeables alors que la méthode par dilution montrait une dilution significative. La raison évoquée était celle de flux croisés au dessus de la cote de 29m. L’analyse des données de descente et de remontée du niveau piézométrique ainsi que l’analyse développée par Drost concernant les méthodes de forage unique, ont permis d’estimer les transmissivités de l’aquifère : 2,049, 2,928 et > 43,88 m2/jour respectivement. La divergence entre les données issues des analyses des descentes et des remontées était attribuée aux pertes de charge hydraulique non linéaires associées aux écoulements turbulents et à des effets d’inertie. La différence entre les résultats des essais de pompage et des résultats de l’analyse de Drost était expliquée par les flux au cours de l’essai hydraulique par pompage qui contourne la zone située à 29 m comme mentionné auparavant.
Resumen
Un conjunto integrado de distintas mediciones han sido usados para estudiar el comportamiento del agua subterranean en un pozo de observación en una formación de roca fracturada, el UK Chalk, bajo condiciones de bombeo y ambientales. Bajo condiciones de bombeo la respuesta de la perforación abierta fue relativamente consecuente con el flujo principalmente concentrado a lo largo de cuatro horizontes discretos de flujo. Más aún se observó una excelente correspondencia entre los tres métodos de mediciones de velocidad de flujo en la perforación: flujímetro de turbina, flujímetro de pulso de calor y pruebas de dilución. Bajo condiciones ambientales el sistema aparecía más complicado. Específicamente, en la mitad superior de la perforación el flujímetro de turbina mostró un flujo importante descendente y el flujímetro de pulso de calor mostró un flujo ascendente casi despreciable mientras que la prueba por dilución indicó una dilución significativa. Se concluyó que esto fue debido a la existencia de un flujo cruzado sobre los 29 m superiores. Los análisis de los datos de depresión, datos de recuperación y un análisis de Drost de los datos de flujo cruzado ambientales arrojaron valores estimados de la transmisividad del acuífero de 2,049, 2,928 y > 4,388 m2/día respectivamente. La discrepancia entre la estimación de la depresión y la recuperación fue atribuida a pérdidas de cargas hidráulicas no lineales asociadas con efectos de turbulencia e inerciales. La diferencia entre los ensayos de bombeo y los resultados de Drost fue explicado por el desvío del flujo en los 29 m de región rocosa, mencionados previamente, durante el ensayo de bombeo.
摘要:
在抽水和自然条件下, 对英国白垩岩裂隙岩层中的一口观测井进行了一系列不同的测量, 以研究其地下水的行为。在抽水条件下, 开放钻孔的响应基本与主要集中在四个分散的水流层的水流一致。此外, 叶轮流速计、热脉冲流速计和稀释法试验三种钻孔流速测量方法呈现出很好的一致性。在自然条件下, 系统表现得更为复杂。特别是在钻孔的上半部, 叶轮流速计表明水流为下降流, 热脉冲流速计表明其为可以忽略的上升流, 而稀释法试验则表明存在着显著的稀释作用。这是由于在上面的29m发生了横向流。降深数据和恢复试验数据分析以及环境横向流数据的Drost分析分别给出含水层的导水系数约为2,049, 2,928 和大于 4,388 m2/d。两种方法给出的导水系数的不同是与紊流和惯性效应有关的非线性水头损失导致的。而抽水试验中水流绕过了前述29 m区域解释了抽水试验和Drost结果之间的不同。
Resumo
Foi utilizado um conjunto integrado de diferentes medições para estudar o comportamento das águas subterrâneas num furo de observação numa formação de rocha fracturada, o cré da formação “Chalk” do Reino Unido, sob condições ambientais e em bombagem. Sob condições de bombagem a resposta do furo foi relativamente linear, com o fluxo concentrado principalmente ao longo de quatro horizontes de fluxo discretos. Além disso, foi observada uma correspondência excelente entre os três métodos de medição da velocidade de escoamento no furo: micromolinete, caudalímetro de impulso térmico, e teste de diluição. Sob condições ambientais o sistema parece mais complicado. Especificamente, na metade superior do furo, o micromolinete mostrou fluxo descendente substancial e o caudalímetro de impulso térmico mostrou fluxo ascendente quase desprezável, enquanto o teste de diluição indicou diluição significativa. Concluiu-se que esta situação se devia a fluxos cruzados que ocorrem nos 29 m superiores. A análise de dados de rebaixamento, dos dados de recuperação, e uma análise Drost dos dados de fluxo-cruzado em condições ambientais, conduziram a estimativas de transmissividade do aquífero de 2,049, 2,928 e > 4,388 m2/dia, respectivamente. A discrepância entre as estimativas para os rebaixamentos e para a recuperação foi atribuída a perdas de carga não lineares associadas a turbulência e efeitos de inércia. A diferença entre o ensaio de bombagem e os resultados Drost foi explicada pelo facto do fluxo, durante o ensaio de bombagem, contornar a zona supracitada de 29 m de rocha.
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Acknowledgements
Funding through the NERC LOCAR research program is gratefully acknowledged (project NER/T/S/2001/00941). The authors would like to thank T. Scott at the Environment Agency, UK, for access to and use of the Bottom Barn abstraction well. The assistance of L. Maurice, D. Buckley, and I. Woods from the British Geological Survey for help in collecting the field data is also gratefully acknowledged.
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Appendix
Appendix
Details of the strike and dip program are as follows. A fracture is identified from a visual inspection of the OTV bitmap image. The user then selects three points anywhere along the fracture intersect: (θ 1, z 1), (θ 2, z 2) and (θ 3, z 3), where 0 < θ < 2π (i.e. north = 0 and south = π) and z [L] is elevation. The program then superimposes the sine wave
where
and
The three points can then be moved independently, and the sine wave automatically corrects itself to fit them. The user can keep moving the points until an appropriate visual fit between the sine wave and the fracture intersect is achieved (see Fig. 8). The final values of (θ 1, z 1), (θ 2, z 2) and (θ 3, z 3) are subsequently stored. The strike and dip of the fracture can then be obtained from
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Butler, A.P., Mathias, S.A., Gallagher, A.J. et al. Analysis of flow processes in fractured chalk under pumped and ambient conditions (UK). Hydrogeol J 17, 1849–1858 (2009). https://doi.org/10.1007/s10040-009-0477-4
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DOI: https://doi.org/10.1007/s10040-009-0477-4