Gas migration in a Cenozoic clay: Experimental results and numerical modelling

Abstract

29Gas migration through a potential host clay formation for the geological disposal of 30 radioactive waste in Belgium is experimentally investigated in the laboratory, and 31 numerical modelling is performed to help in the interpretation of the results. Selected 32 air injection tests under oedometer conditions on initially saturated Boom Clay samples 33 with oriented bedding planes are presented in the paper. Priority in the experimental 34 programme was given to the study of the deformation response along the injection and 35 dissipation stages, as well as to the analysis of the pore network changes, which detect 36 the opening of fissures that can act as preferential air pathways. The experimental 37 results were simulated using a fully coupled hydro-mechanical finite element code, 38 which incorporates an embedded fracture permeability model to account for the 39 simulation of the gas flow along preferential pathways. Clay intrinsic permeability and 40 its retention curve were assumed to be dependent on strains through fracture aperture

Studying the thermal conductivity of a deep Eocene clay formation: Direct measurements vs back-analysis results

“…A parameter  =0.0733 can be obtained for saturated conditions by fitting experimental results. For a fissure aperture associated with the dominant pore mode of b = 7×10 -7 m (refer to section 2), the separation between fissures is a = 9.5×10 -6 m ( [18] reports a value a = 3×10 -5 m for Boom Clay dealing with gas migration through pressure-dependent fissures). Figure 8 shows the fitted results at full saturation for the two orientations (λ// = 2.08 Wm -1 K -1 , λ  = 1.84 Wm -1 K -1 and T = λ// / λ  = 1.13).…”

“…The largest pores are related to macropores and fissures (see for instance Ref. [18] for an equivalent separation of the pore domains in Boom Clay). I.N.I.S.Ma [10] reported a microporosity (pore sizes < 30 nm) around 0.17 at the depth of interest.…”

Gas transport in granular compacted bentonite: coupled hydro-mechanical interactions and microstructural features

“…This lateral stress should be close to the vertical stress for approximately the normally consolidated conditions prevailing at the beginning of the injection: K oNC =1-sinφ′ ≈0.9 (for an estimated drained friction angle for MX-80 of φ′ = 8º). A minimum of 1 MPa can be accepted as the difference between maximum air pressure and vertical stress to avoid preferential air flows between the sample and oedometer ring [11]. The pressure at the downstream vessel was kept at 0.50 MPa during the whole process.…”

Themed Issue on Selected Papers SEG2015 — Part I

“…Two contributions of this special issue are related to this type of application, one of them focused on gas migration and the other one on coupled processes associated with water transfer under non-isothermal conditions. The paper by Gonzalez-Blanco et al 8 explores gas migration issues through a potential host clay formation for the geological disposal of radioactive waste in Belgium on the basis of laboratory work and its numerical modelling to help in the interpretation of the results. Priority was given to the study of the volume change response along the air injection and dissipation stages that were performed under oedometer conditions, as well as to the analysis of the pore network changes (associated with preferential air pathways).…”