engleski

Flow-dependence of matrix diffusion in highly heterogeneous rock fractures

Diffusive mass transfer in rock fractures is strongly affected by fluid flow in addition to material properties. The flow-dependence of matrix diffusion is quantified by a random variable ("transport resistance") denoted as β [T/L] and computed from the flow field by following advection trajectories. The numerical methodology for simulating fluid flow is mesh-free, using Fup basis functions. A generic statistical model is used for the transmissivity field, featuring three correlation structures: (i) highly connected non-multi-Gaussian ; (ii) poorly connected (or disconnected) non-multi-Gaussian ; and (iii) multi-Gaussian. The moments of β are shown to be linear with distance, irrespective of the structure, after approximately 10 integral scales of ln T. Percentiles of β are found to be linear with the mean β when considering all three structures. Taking advantage of this property, a potentially useful relationship is presented between β percentiles and the fracture mean water residence time that integrates all structures with high variability ; it can be used in discrete fracture network simulations where T statistical data on individual fractures are not available.

attenuation; diffusive mass transfer; heterogeneity structure; retention; rock fractures; transport

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