Fluids are expected to profoundly modify the seismic properties of the cracked rocks of the Earth's upper crust but so far there are few relevant laboratory measurements.
With funding from the Australian Research Council we are developing novel experimental techniques to build a better laboratory-based understanding of the seismic properties of fluid-saturated crustal rocks. The outcome will be an improved capacity to monitor the presence of fluids in diverse situations ranging from geothermal power generation and waste disposal to upper-crustal fault zones. Synthetic 'sandstones' with distinctive microstructures have been prepared by sintering close-packed spherical glass beads of uniform diameter - a procedure previously employed by collaborator Professor Douglas Schmitt of the University of Alberta. The temperature and duration of sintering can be varied to achieve a wide range of porosity, consisting at sufficiently low porosity, of isolated pores. Such microstructures can be modified by thermal cycling to introduce cracks that typically connect otherwise isolated pores, thereby providing an interconnected network in three dimensions. Such simple, permeable, microstructures are expected to be useful in understanding how the seismic properties of porous/cracked rocks are affected by fluid saturation.
The project aims to use laboratory forced-oscillation methods to explore the seismic properties of such synthetic rocks saturated with fluids of appropriate viscosity.