Pore Space Geometry (PSG)

The boreholes for the PSG experiment were drilled in January 2004. The core material from the injection borehole was found to be completely homogenous matrix to a depth of around 1.3 metres. The cores from the injection borehole are shown below.

Core material from PSG injection borehole - sections shown below in higher resolution

Section 1

Section 2

Section 3

Section 4

Section 5

Sections from the cores were sent to Finland for lab based porosity measurements (see the Support of in-situ test section).

The drilled PSG boreholes in the WT tunnel with the air ventilation system in place

Pore Space Geometry (PSG) Experiment

The in-situ test took place in the WT tunnel at the Grimsel Test Site.

Location of the WT tunnel in the Grimsel Test Site

 View the tunnel with the PSG experiment in our Virtual Tour of the GTS section

Planned borehole layout

The planned stages are shown in the computer animation below

PSG animation

Drilling of injection borehole. Drilling of observation boreholes Resin injection Polymerisation of resin Overcoring - removal of core.

Pore Space Geometry (PSG) Experiment

Material from the central borehole of the in-situ test was send to Helsinki for laboratory based impregnation with C14-PMMA. This gave a first indication of the porosities expected to be found during the in-situ impregnation (if estimates of stress release are accounted for).

The photomicrograph and corresponding autoradiography from the inlet hole are shown below.

Photomicrograph of a section of the core from the inlet hole of the in-situ test

Corresponding autoradiograph of the core from the inlet hole of the in-situ test

The digital autoradiographs found the measured porosities to be between 0.45 and 0.55 %, which is within the range observed at the GTS via other methods. This measurement was taken at a depth of around 80cm from the tunnel wall and well outside of any Excavation Disturbed Zone (EDZ). The next stage was to apply this methodology: Pore Space Geometry (PSG) - In-situ Experiment.
 

Pore Space Geometry (PSG) Experiment

Research at the University of Helsinki has involved two stages of laboratory test. In the first, rock cores were impregnated with 14C-PMMA before polymerisation of the resin with a ⁶⁰Co source. The degree of resin impregnation was then observed using beta autoradiography with KODAX beta film. These films can then be digitised and a quantitative measurement of the degree of impregnation could be made.

The first results of the in-situ 14C-PMMA method development work with laboratory scale
tests of Grimsel granodiorite are shown below.

Uranine dyed water impregnation

Eosine dyed PMMA impregnation

Photomicrograph of rock surface of Grimsel granodiorite sample and corresponding autoradiograph provided by 14C-PMMA impregnation. Magnifications from three different areas corresponding to porosities of 0.3, 0.5 and 0.7%. Sample width is 67 mm. The magnified areas show that, within a relatively small sample, there are large changes in the measured porosity.

The next stage is to carry out resin impregnation on larger samples and use similar techniques to the in-situ test at the GTS.

Block scales tests were carried out on 30 x 30 x 30 cm blocks of Kuru grey granite from Finland. The large blocks were prepared in the same manner as the in-situ test. To simulate in situ conditions, the blocks were kept wet by leaving them in a tray of water. The purpose of the heating phase was to then dry out the rock matrix before the injection of the 14C-MMA. After injection of the resin, more heat was applied, via the central borehole, to begin the polymerisation. Once the polymerisation was complete, the block could be cored and autoradiography carried out on the samples. The equipment for the block tests is shown below.

The equipment for the block scale test using (30x30x30 cm) Kuru grey granite from Finland.	The start of the heating tests using the Kuru grey granite.
The equipment for the block scale tests. The block sits in a tray of water to simulate near saturated conditions. This tests the drying procedures. The Perspex box prevents evaporation of water to the laboratory
After the injection of the 14C-MMA, the block is heated to allow polymerisation. Cores of the polymerised block are then taken for autoradiography as shown in the following animation.   {flv width="320" height="260" img="videos/kura_block_thumb.jpg"}kura_block{/flv} PSG Kura block animation

The resulting images from the block scale test are shown below
Photomicrograph of rock surface of Kuru grey granite. Sample length is 70mm	Corresponding autoradiograph provided by lab based 14C-PMMA impregnation.	Magnification of a 1 cm2 area of the autoradiograph showing good impregnation of 14C-PMMA into the fine pore space

Beta autoradiograph of the block test material. The dark areas show the location of the 14C tracer in the pore space of the rock

Modelling of the laboratory and in-situ test data is carried out by colleagues at the University of Poitiers in France. The aim is to improve existing transport models via visualisation and quantification of matrix porosity, degree of connected porosity, pore tortuosity and pore constrictivity.

Pore Space Geometry (PSG) Experiment