Oral Presentation Australasian Groundwater Conference 2017

CT imaging and centrifugation to characterise dual porosity fluid flow and solute transport  (331)

Wendy Timms 1 2 , Richard Crane 3 , Ji-Youn Arns 4 , Mark Cuthbert 5 , Ian Acworth 1 6 , Christoph Arns 4
  1. Connected Waters Initiative Research Centre, UNSW Australia, Sydney
  2. UNSW School of Mining Engineering, Australian Centre for Sustainable Mining Practices, Sydney, Australia
  3. Cardiff University, Cardiff, UK
  4. UNSW School of Petroleum Engineering, Sydney, Australia
  5. University College London, London, UK
  6. UNSW School of Civil and Environmental Engineering, Sydney, Australia

Advanced techniques including CT imaging and centrifugation can be combined to characterise flow and solute transport through dual porosity and low permeability media. Observing and quantifying physio-chemical influences on the migration and attenuation of contaminants through geological media with both matrix and preferential flow paths is difficult. We present examples of combining advanced techniques to characterise these processes within semi-consolidated soil samples and rock cores, including centrifugation (steady-state and interrupted flow methods) and CT imaging (static fluids and dynamic flow). For example, a new centrifugation method was developed to measure the effective porosity of a clayey-silt soil with preferential flow paths using a non-reactive flow tracer. Experimental and numerical modelling results (Crane et al. 2015) were consistent with field tests showing relatively high vertical permeability (Timms et al. 2016). 3D CT imaging of these soil samples at a resolution of 49 micron is providing statistics on pore throat networks and the associated topology (connectivity) between large pores. Other examples of advanced core characterisation include comparisons of sandstone permeability with variable solute chemistry, using either de-ionized or formation fluids. CT imaging of these rock cores reveals the micro-scale relationship between pore spaces, swelling and mobilisation of clay particles, and the mineral matrix. Differences in permeability between centrifugation tests and other core permeability methods highlight the importance of testing under in-situ conditions.

Future research could combine field investigations with these experimental techniques to improve estimates of effective porosity and long term physio-chemical interactions. Advanced centrifugation and CT techniques could apply to many porous media challenges including long term corrosion of concrete, in-situ leach extraction of commodities, long term integrity of porous water treatment membranes and the performance of barriers for carbon sequestration, mine tailings and nuclear waste disposal.

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