Tracer transport in a fractured chalk: X-ray CT characterization and digital-image-based (DIB) simulation |
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Authors: | W C Zhu J Liu D Elsworth A Polak A Grader J C Sheng J X Liu |
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Institution: | (1) School of Oil and Gas Engineering, The University of Western Australia, WA, 6009 Crawley, Australia;(2) Department of Energy and Geo-Environmental Engineering, Penn State University, University Park, USA;(3) Department of Civil and Environmental Engineering, Technion, Israel Institute of Technology, Haifa, 32000, Israel |
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Abstract: | A digital-image-based simulation methodology is applied to evaluate the influence of heterogeneous porosity on the evolution
of tracer concentrations in imaged tracer tests. Maps of computed tomography (CT)-number are calibrated relative to average
porosity, and then thresholded to define porosity maps. These data are then used to automate the distribution of parameters
within a finite element representation of the geometry. The technique is applied to characterize the variability of the porosity,
the hydraulic conductivity, and the diffusivity for an artificially fractured chalk core (30 × 5 cm). X-ray CT was used both
to characterize the initial condition of the core, and then to concurrently monitor the transport of an NaI tracer within
the fracture and into the surrounding matrix. The X-ray CT imaging is used to characterize the heterogeneous rock porosity,
based on which the hydraulic conductivity, and diffusivity of the chalk were defined and were directly imported into our newly
developed three-dimensional FEMLAB-based multiple physics simulator. Numerical simulations have confirmed the observed tracer
transport behaviors: (1) The different tracer-penetration distances imaged in the matrix above and below the horizontal fracture
are indicative of a greater tracer mass penetrating into the lower matrix; and (2) Transport in the matrix below the fracture
was enhanced. The computer simulated tracer concentration distributions compare favorably with those monitored by X-ray CT. |
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Keywords: | Tracer diffusion Rock heterogeneity Porosity DIB simulation Imaging |
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