Engineered damage zone sealing during a water injection test at the Tournemire URL

Abstract

Low-permeability clay formations provide good candidate host rocks for geological disposal of radioactive waste, because there is expected to be limited movement of gas or water through the formation. However, when constructing tunnels, the stress state in the formation around the tunnel will change, which can lead to damage to the formation, changing the bulk hydraulic properties of the formation close to the tunnel. There is the potential for this damaged zone to act as a preferential pathway for fluid flow and radionuclide transport. A water injection experiment is ongoing at the Tournemire underground rock laboratory to investigate the hydraulic properties of the Toarcian argillite in which the laboratory is constructed. Water is injected into the formation at the end of a sealed borehole and moves preferentially in the damaged zone along the borehole walls. The rate of water injection into the rock changed over the first year of the experiment and the causes of this change are investigated in this paper by numerical modelling. The study demonstrates that the change in water injection rate into the argillite can be explained by the evolving hydraulic properties of the damaged zone around the borehole. The findings of the modelling study are discussed in the context of long-term radioactive waste disposal.

Chemo‐Mechanical Coupling in Fractured Shale With Water and Hydrocarbon Flow

“…Both water uptake and volumetric strain in claystones are in fact very small (in the order of a few percent in mass/volume; Minardi et al., 2016), with the extent of swelling depending on water chemistry (Giot et al., 2019) and water content (McBrayer et al., 1997), in addition to clay mineralogy. These unique features of claystones provide a means to engineer the self‐sealing process through artificial re‐saturation with formation fluids (Thatcher et al., 2016). However, studies have largely been focusing on the use of water as a permeant and are not necessarily valid in the presence of nonaqueous liquids (McBrayer et al., 1997).…”

A new hydro-mechanical model for bentonite resaturation applied to the SEALEX experiments

“…The different boreholes are used to test different ratios of bentonite to sand in the seals and the form of the bentonite sand mixture, for example, precompacted blocks or pellets. The Toarcian argillite is an indurated clay formation consisting of shales and marls, with a very low permeability to saturated water flow (~10 -21 -10 -18 m 2 ), significant porosity (~9%) and with a strong tendency to show hydraulic 'self-sealing' characteristics post excavation (Thatcher et al, 2016).…”

“…The data that were collected from the experiment showed some trends that are not readily understandable based on the description of the experiment, so the models were expected to only match average behaviour and not to fit the all the variations seen in the data. Evidence from the water injection test (Thatcher et al, 2016) indicates that hydraulic interactions with the host rock are not likely to be of significance over the timescales of relevance to the experiment (~9 months) and, given the aspiration to fit general trends from the data, it was decided to model the seal without the host rock.…”

DECOVALEX-2015: an international collaboration for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in geological systems

“…and the in situ experiments(Millard et al 2017). Detailed results from individual modeling groups can be found inThatcher et al (2016a, b), FraserHarris et al (2016),Mokni (2016),Xu et al (2016), Thatcher et al (2016a). investigated Excavation Damage Zone (EDZ) sealing during a water injection test at the Tournemire URL.…”