Parallel Session B-1 - Mini-Symposium: Gas migration in geomaterials

In this study we have used NMR to image the diffusion and interaction in porous media. NMR is one the few methods by which H2-gas can be directly imaged in porous media. In order to do so, we have constructed a special NMR setup to measure quantitatively the H2 gas content in porous media up to 60 bar. The first initial results of the measurement will be discussed.

- Gas diffusion in partially saturated clay based materials in the context of nuclear waste disposal. - Preliminary modelling to predict the behavioral trend of diffusing gases in unsaturated clay based materials. - Experimental study on cross diffusion of gases through unsaturated synthetic clay samples.

This article presents the work carried out by the CTU in Prague and ÚJV Řež as part of Task 2 of the GAS Work Package of the EURAD project. Since the Czech deep geological repository concept is considering the use of local bentonites, the research programme is focusing on Czech BCV bentonite and its benchmarking comparison with foreign materials such as MX-80 sodium bentonite. The laboratory testing programme involves the performance of gas breakthrough tests on water-saturated compacted bentonite samples. The key contribution of the research concerns the direct use of hydrogen as the gas injection medium.

Gas breakthrough pressures have been determined for the reference bentonite in the Spanish concept for geological disposal of radioactive waste. Long term breakthrough time curves showed a consistent and systematic repetition of breakthrough values; and changes in the slope of the curves could indicate the different flow types and the underlying physical concepts. Breakthrough pressures increased with increasing dry density and water content at compaction, and the geometry of the sample (decreasing L/D ratio). They were much lower than the air entry pressure and close to the upper range of the expected swelling pressure, supporting the propagation of dilatant.

● Pneumo-Hydro-Mechanical (PHM) Finite Element model to simulate gas migration in saturated clay samples, using triple-node zero-thickness interface elements to explicitly represent gas fracturing. ● The model is validate against experimental gas fracturing tests from other authors. ● The simulations show that the model proposed can reproduce the experimental results, providing valuable insights into the factors controlling the onset and propagation of the gas fractures.

In order to understand different transport mechanisms involved, numerical simulations were performed, and the results were compared with laboratory data. In the framework of the EURAD/GAS project, a gas pressure dependent permeability model was implemented into the finite element code OpenGeoSys 6. Two types of gas injection tests carried out by the Institute for Rock Mechanics (IFG GmbH) and a gas injection test performed by École Polytechnique Fédérale de Lausanne (EPFL) were employed to investigate the gas transport through Opalinus Clay. The wet phase (water) was immobile in IFG experiments and was displaced by gas in EPFL experiment.