We can't apply the conventional steady state method since pressure drop across the core would be too small to measure and shale can have natural fractures to bypass the fluid. I have heard that pulse decay permeameters are capable of measuring ultra low permeability. If someone can help providing with the procedure of measuring permeability with pulse decay permeameter, I would be grateful.
The nuclear waste repository people are specialized in this. There is more to say than I could press it in this answer. You may want to check NAGRA.ch for publications. On pulse methods, one or two of my papers (uploaded here) may help you as well.
Dear Rupom,
as Cristian Enachescu mentioned, there are a few companies performing such tests down to permeabilities of 10E-21 or 10E-22 m2. Most of them test with a pulse decay but in certain cases also long-term (weeks) hydraulic constant head or rate tests are performed with very small rate flowmeters. For references I would suggest to look up the Nagra Technical Reports (NTB) and in partiuclar those dealing with "Opalinus Clay" available online. Hope that helps!
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