The main field work began in April 2004.
To ensure the matrix pore water would not interfere with the injection of the resin, the rock around the injection site was gently heated. After 3 weeks of heating, the rock matrix was thought to be unsaturated and the injection of resin could begin.
The PSG site was fully instrumented with the specialised resin injection/heating equipment in April 2004. An integrated packer system containing both the resin injection equipment and the heater required for the polymerisation of the resin in situ were placed in the central borehole.
Along with the C-14 doped resin, a fluorescent tracer was also added to the resin. This allows the suitability of the C-14 tracer to be compared with that of fluorescent dyes and also allows us to be completely sure that all resin was removed in the overcore (by examining the overcored borehole with a UV lamp).
The integrated resin injection and heating packer is emplaced by Christoph Bühler of Solexperts
When illuminated with UV light, the tracer dye in the resin fluoresces
Injection of resin continued for four weeks. The injection was terminated and the resin injection equipment disconnected. The heater unit was then connected to the data acquisition system and the output to provide the correct temperature in the measuring boreholes.
Graph of injected mass of resin (blue line) and the flow rate of resin injection against time (hours). Around 50g of resin was injected into the rock matrix.
Heating graph for the PSG experiment. The heater unit in borehole PSG 04.001 is shown by the red line. The response in the observation boreholes (green and blue lines) at 15 cm distance from the injection hole are also shown. The steps in the graph of PSG 04.001 correspond to manual adjustments of the heater. The difference between PSG 04.005 and PSG 04.006 are related to the positioning of the downhole temperature sensors.
After two weeks of heating, the polymerisation was assumed to be complete. Overcoring was carried out by Grimsel staff using a Hilti single barrel corer with a 30 cm diameter drill bit. Drilling was successful and excellent core recovery was achieved.
The overcoring was successfully carried out by Hans Abplanalp of Nagra using a Hilti drill machine with a 30 cm diameter drill bit.
The large diameter overcore was made of a very homogeneous granite as planned.
The recovered overcore was then sent to the University of Helsinki for detailed analysis.
The large core was then sub-sampled in Finland
In Finland, the core was sawn into seven pieces and these are currently undergoing analysis for the resin distribution profiles and porosity determinations.
Pore Space Geometry (PSG) Experiment