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• Coupling flowmeter and pumping test data for low-cost 3D aquifer characterizations. • 3D hydraulic conductivity distribution is assessed from an inverse approach. • The effectiveness of integrating the two datasets is studied with 3D synthetic models. The accurate characterization of the underground depositional structure and hydraulic property distribution is essential to understand flow and solute transport in heterogeneous rocks or soils. Hydraulic tomography was shown to be an efficient technique to infer the spatial distribution of hydraulic properties. Due to the fact that information about the sedimentary structures' distribution is not always available to allow a three-dimensional characterization, many of existing field applications of hydraulic tomography have been limited to two-dimensional imaging along horizontal layer or vertical profiles where hydraulic data were collected. In this work, we explore the potential of combining tomographic pumping and flowmeter tests responses in an inverse approach for three-dimensional aquifer characterization. The tomographic pumping data provide information about the lateral hydraulic connections between boreholes, while the flowmeter data constrain the vertical heterogeneity structure. The inverse approach is first validated using two synthetics models composed of multi-layered depositional structures and heterogeneous hydraulic properties within each layer. It is shown that adding the information provided by the flowmeter profiles, the inverted model exhibits more realistic depositional features. We then apply the proposed approach to characterize the 3D hydraulic conductivity field controlled by sedimentary structure of an experimental site in layered porous rocks. The inverted hydraulic conductivity field is in a good agreement with permeability measurement on drilled cores. The proposed method offers an efficient and low-cost approach for rapid assessment of the hydraulic properties in 3D and could be extrapolated to other field applications. [ABSTRACT FROM AUTHOR]

We develop a new numerical model that couples hydraulic, mechanical and chemical processes to investigate the dynamic influence of stress on incipient karst formation in natural fracture networks. Our geological models are constructed based on realistic fracture patterns mapped from outcrops, which capture a wide range of spatial distribution and organization of carbonate fracture networks. We simulate the dissolutional growth of karst conduits in the fractured formation under varied initial aperture distribution and in-situ stress loading. We found that the impact of the stress effect on karstification depends on the relative relationship between the flow direction and the structural anisotropy of the fracture network. When the flow occurs in the direction corresponding to the most continuous fracture network structures, karst conduits only develop locally along a few long fractures with an orientation favorable to frictional sliding under the differential stress. Indeed, the important shear-induced dilation of these fractures generates a higher aperture and thus hydraulic conductivity. In contrast, when flow is in the direction transverse to the most continuous fractures, the far-field stress loading has a negligible impact on the emergent dissolution pattern but a perceptible impact on the onset time of breakthrough. In this later case, the developed conduits are much more tortuous with many branches. In both cases, the presence of initial aperture variability facilitates the development of a uniform dissolution front and therefore delays breakthrough. Our results demonstrate that the heterogeneity induced by geometrical complexities, enhanced by in-situ stress conditions, may play a decisive role on the karstification processes in fractured rocks. The results from this research provide important insights into the spatial relationship between tectonic structures, geomechanical constraints and karstogenesis. [ABSTRACT FROM AUTHOR]