Technical Report NTB 03-11

Grimsel Test SiteInvestigation Phase VGAM – Gas Migration Experiments in a Heterogeneous ShearZone of the Grimsel Test Site

This report documents the scientific investigations carried out as part of the GAM project between June 1997 and April 2001 at the Grimsel Test Site (GTS) within the framework of Investigation Phase V (1997 – 2001). Four radioactive waste management organisations participated in the GAM experiment, namely ANDRA, ENRESA, NAGRA and Sandia National Laboratories (SNL) for the US Department of Energy (DOE). The experiment team consisted of the delegates of the participating organisations, research groups from the Swiss Federal Institute of Technology / Zurich and from the Technical University of Catalonia / Barcelona and, last but not least, several contractor teams.

Essential aims of the GAM investigation programme were the development and testing of laboratory and field equipment for tracer experiments. Innovative laboratory technologies were applied, such as Laser Scanning Confocal Microscopy and X-ray tomography, flow visualisation in artifical fractures, nuclear magnetic resonance measurements and neutron radiography. Furthermore, a new technique was tested for the recovery of well preserved core samples from the GAM shear zone. Novelties in field testing comprised the use of an on-line counter for the particle tracer tests and a georadar survey of gas and brine injection tests with a high frequency borehole antenna.

The development of upscaling methodologies and the derivation of effective parameters for single- and two-phase flow models was another issue of interest. The investigations comprised theoretical studies on solute transport in non-uniform flow fields and assessment of the impact of the microstructure on solute and gas transport. Closely related to these theoretical studies was the numerical interpretation of the combined solute and gas tracer tests, which revealed the great potential of such data sets with regard to model discrimination.

As a final step in the synthesis task of the GAM project, a model abstraction process was established, aimed at integrating the descriptive studies on various scales with the hydraulic investigations to produce a consistent conceptual model of flow and transport processes in the heterogeneous shear zone.