BGS has developed a new technique for the investigation of fluid flow through low-permeability materials. Such investigations are critical to ascertaining the viability of underground sites for the containment of spent materials produced from the energy industry, including carbon dioxide and radioactive waste. The new technique uses a mixture of gold and titanium nanoparticles to trace fluid flow.
Nanoparticles are injected within a stream of helium into a rock sample under pressure. After the sample is depressurised, it is sliced and imaged microscopically with a scanning electron microscope (SEM). The progress of the nanoparticles through the material can then be analysed by mapping the concentrations of titanium and gold.
In order to determine the gas transport properties of rocks, a number of different experimental methodologies have been developed by different testing laboratories. The timescales allowed for testing vary greatly, as do the pressure regimes and flow geometries. Direct comparison of approaches used between testing laboratories has not previously taken place.
Our results represent the first direct observations of a previously only hypothesised mechanism for gas transport. Current models of fluid flow in these materials do not generally allow for such a mechanism. As such, this evidence provides a fundamental insight into the processes that govern seal surety, as well as demonstrating the value of the technique as a tool to aid further investigation. The results will help to improve the interpretation of experimental work and inform modelling efforts. Such work is crucial for the reliable performance assessment of geological storage systems.
Please contact Dr Caroline Graham for further information