Comparative study of methods for estimating a permeability profile across the Opalinus Clay at the Mont Terri rock laboratory (DB Experiment)

Catherine Yu (1) , Mustafa Al Reda (2) , Jean Michel Matray (1) , Guillaume Berthe (3) , Julio Goncalves (4) , David Jaeggi (5)

1 IRSN/PSE-ENV/SEDRE/LETIS - Laboratoire d'étude et de recherche sur les transferts et les interactions dans les sous-sols
2 UPSUD - University of Paris Sud
3 IFPEN - IFP Energies nouvelles
4 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
5 Office fédéral de topographie swisstopo

The goal of this study is to acquire and validate a permeability profile for modelling fluid flow across a compacted clayrock. The chosen place for the comparison is the 250m deep inclined borehole BDB-1 performed in the hydraulically undisturbed zone of the Opalinus Clay, at the Mont Terri rock laboratory (Yu, 2015). Four different methods were applied: two on air-drilled core samples for i) petrophysical measurements at IRSN by applying a Poiseuille-type law specific to a plane parallel geometry (Yu, 2015) and ii) gas permeability measurements at IFPen by using a Hassler cell at constant gas pressure gradients (Al Reda, 2016). Two other methods involved in situ hydraulic testing through a multipacker system installed in BDB-1 with iii) Transient Pulse Tests (TPT) and iv) Constant Rate Withdrawal Tests (CRWT) (Yu, 2015). Hydraulic conductivities obtained by numerical inversion from TPT are consistent with those deduced from CRWT, and suggest a vertical facies-dependent variability across the formation. The Opalinus Clay shaly facies shows higher values (ca 10-12 m∙s-1) than its sandy facies (ca 10-13 m∙s-1). In situ test also allowed selecting a cementation factor of 2 for petrophysical estimates of intrinsic permeabilities. The values obtained are globally in good agreement with the ones previously obtained at the rock laboratory and in the hydraulically disturbed zone. At last, the steady state method in Hassler cell provided apparent gas permeability values on a selection of samples also analysed for the petrophysics method (Al Reda, 2015). Results obtained were corrected of the Klinkenberg effect and indicate values consistent for intrinsic permeabilities obtained by the two lab methods. They also validated a value of 2 for the cementation factor. The selected vertical profile of hydraulic conductivity across the Opalinus clay is that deduced from petrophysics and was validated by four independent methods. It is now available for modelling flow transport across the claystone. Yu C. (2015) DB Experiment: Comparative study of convective and diffusive transport phenomena within the Opalinus Clay at Mont Terri. Mont Terri Technical Note 2015-53 Al Reda M. (2016) Comparative study of methods for assessing permeability on Opalinus clay samples. Master 2 internship report.

Domaines: Sciences de l'environnement

Catherine Yu, Mustafa Al Reda, Jean Michel Matray, Guillaume Berthe, Julio Goncalves, et al.. Comparative study of methods for estimating a permeability profile across the Opalinus Clay at the Mont Terri rock laboratory (DB Experiment). 25ème Réunion des Sciences de la Terre, RST 2016, Oct 2016, Caen, France. ⟨hal-02869294⟩