Characterisation of Gas Transport Properties of the Opalinus Clay, a Potential Host Rock Formation for Radioactive Waste Disposal

Marschall, P.; Horseman, S.; Gimmi, Thomas (2005). Characterisation of Gas Transport Properties of the Opalinus Clay, a Potential Host Rock Formation for Radioactive Waste Disposal. Oil & Gas Science and Technology, 60(1), pp. 121-139. Ed. Technip 10.2516/ogst:2005008

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The Opalinus Clay in Northern Switzerland has been identified as a potential host rock formation for the disposal of radioactive waste. Comprehensive understanding of gas transport processes through this low-permeability formation forms a key issue in the assessment of repository performance. Field investigations and laboratory experiments suggest an intrinsic permeability of the Opalinus Clay in the order of 10(-20) to 10(-21) m(2) and a moderate anisotropy ratio < 10. Porosity depends on clay content and burial depth; values of similar to 0.12 are reported for the region of interest. Porosimetry indicates that about 10-30 of voids can be classed as macropores, corresponding to an equivalent pore radius > 25 nm. The determined entry pressures are in the range of 0.4-10 MPa and exhibit a marked dependence on intrinsic permeability. Both in situ gas tests and gas permeameter tests on drillcores demonstrate that gas transport through the rock is accompanied by porewater displacement, suggesting that classical flow concepts of immiscible displacement in porous media can be applied when the gas entry pressure (i.e. capillary threshold pressure) is less than the minimum principal stress acting within the rock. Essentially, the pore space accessible to gas flow is restricted to the network of connected macropores, which implies a very low degree of desaturation of the rock during the gas imbibition process. At elevated gas pressures (i.e. when gas pressure approaches the level of total stress that acts on the rock body), evidence was seen for dilatancy controlled gas transport mechanisms. Further field experiments were aimed at creating extended tensile fractures with high fracture transmissivity (hydro- or gasfracs). The test results lead to the conclusion that gas fracturing can be largely ruled out as a risk for post-closure repository performance.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences

UniBE Contributor:

Gimmi, Thomas

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

1294-4475

Publisher:

Ed. Technip

Language:

English

Submitter:

Thomas Gimmi

Date Deposited:

06 Oct 2014 14:53

Last Modified:

14 Dec 2014 10:06

Publisher DOI:

10.2516/ogst:2005008

BORIS DOI:

10.7892/boris.47675

URI:

https://boris.unibe.ch/id/eprint/47675

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