Pore Space Geometry (PSG) - Laboratory Experiments & Modelling - Method Development

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

Experiments using fluorescent dye tracers to impregnate (via a central hole) a sample of oven dried Grimsel granodiorite . Impregnation time was 2 hours. This test compares the pore space that can be accessed with water and with PMMA.

 

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.
 

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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

The GTS underground facilities are also available to interested 3rd parties for underground testing and research. The GTS offers cost-effective access to a fully developed, well characterised underground research facility with round the year logistical support - please contact Dr. Ingo Blechschmidt, Head of the Grimsel Test Site, for further details.