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A numerical investigation to illustrate the consequences of hydraulic connections between granular and fractured-rock aquifers 总被引：1，自引：1，他引：0
Natural or artificial hydraulic connections between a granular aquifer in contact with a fractured-rock aquifer can have significant physical and chemical impacts at both a local and a regional scale. In this study, numerical simulations are conducted in order to illustrate the hydrogeological consequences of such hydraulic relationships. The numerical investigation, based on a conceptual model, focuses on the effects of the hydraulic connections when conducting a pumping test in a well that is set into a granular confined aquifer overlying a fractured-rock aquifer which presents a few fractures directly connected to the granular aquifer. It is illustrated that when interpreting the pumping test with the conventional methods consisting of plotting the drawdown versus time, a bias is introduced on the estimation of the transmissivity of the granular aquifer due to groundwater flowing from the fractured-rock aquifer via connecting fractures. However, it is underlined that plotting drawdown log-derivative versus time helps to diagnose the existence of these hydraulic relationships and therefore avoids committing a bias on the transmissivity estimation of the granular aquifer. Numerical simulation results also illustrate that hydraulic connections between the two aquifers can have significant impacts on the hydrogeochemical signature of the granular aquifer under investigation. 相似文献
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Hydrogeology Journal - Adequate groundwater management requires models capable of representing the heterogeneous nature of aquifers. A key point is the theoretical knowledge of flow behaviour in... 相似文献
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Pumping tests in discontinuous media are commonly interpreted using radial/non-radial flow analytical models, which do not account for a large range of multistage real signatures that combine both flow types. The term radial is employed in Barker??s sense, referring to the cross-flow area growth with a flow dimension (n) equal to 2, while multistage refers to a flow response of several time periods with successive n values. Synthetic domains are used to numerically investigate the flow behaviour of faulted media, specifically the effect of fault inclination on multistage signatures. Simulations are performed using single faults surrounded by a permeable matrix to characterize drawdown series and to identify hydrodynamic scenarios associated with some diagnostic multistage n sequences. The n sequence 2 ?C <?2 ?C 2 results from interactions between the matrix and a horizontal to weakly inclined fault, while 2 ?C 1.5 ?C 2 corresponds to a higher fault inclination and is a combination of the generalized horizontally and vertically faulted models. These results improve the interpretation of ambiguous drawdown series from long-term pumping tests. This provides a better hydraulic characterization of faulted environments, allowing assessment of fault and matrix properties such as fault inclination. The approach is successfully tested on real datasets. 相似文献
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The objective of this work is to explore the use of flow dimensions as a tool for characterizing hydraulic conditions in faulted media. Transient flow is numerically simulated in synthetic vertically-faulted reservoirs. Analysis of the obtained time series following the Generalized Radial Flow (GRF) model displays combined radial and fractional signals with a flow dimension n=1.5. Investigating the transient geometry of the frontal equipotential surface shows that fractional flow occurrence is due to abnormal fault diffusion as a consequence of water supply from the matrix under specific conditions. An original hydrodynamical explanation for fractional flow in vertically faulted media is suggested, along with a reinterpretation of the bilinear regime. It is shown that the GRF theory remains valid in such discontinuum as the fundamental relationship between n and the cross-flow area is satisfied. These results provide insights in the use of the flow dimension as a hydraulic diagnostic tool in faulted media. 相似文献
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Sandra K. Richard Romain Chesnaux Alain Rouleau Roger Morin Julien Walter Silvain Rafini 《Hydrogeology Journal》2014,22(8):1889-1904
Field evidence of hydraulic connections between a bedrock aquifer and an overlying granular aquifer in the Canadian Shield (Grenville Province) is presented. This issue is rarely considered and investigated despite its important hydraulic and chemical consequences and its widespread occurrence worldwide. The methodology employed is based on complementary field tests conducted at specific experimental sites instrumented both in the rock and in the overlying deposits. One of the bedrock sites revealed a natural hydraulic connection with the overlying granular aquifer caused by the weathered surface of the uppermost bedrock. Another site revealed an artificial hydraulic connection between the bedrock and the granular aquifer created by an improperly sealed casing. A regional study showed that hydraulic connections yield an erroneous interpretation of the true hydraulic properties of the tested aquifer. The detection of hydraulic connections is therefore essential to properly define well-capture areas and contamination conditions. It is recommended to practitioners that pumping tests be performed as well as hydrochemical comparisons of each existing aquifer unit. Falling-head permeability tests are also helpful in verifying the quality of the seal at the bedrock–casing contact. More effective procedural controls and better well-construction practices are necessary to reduce the risks of cross-contamination induced by defective seals. 相似文献
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