Laboratory measurements of ultralow permeability of geologic materials

A new apparatus is described for determining permeability (water) in geologic materials as a function of confining pressure (to 200 MPa), pore pressure (to 25 MPa), and deviatoric stress (500–800 MPa). The samples are relatively large (0.15 m diameter ×0.28 m long) and may be intact or contain a single through‐going fracture. Permeabilities of 10−11–10−24 m2 (10–10−12 D) may be measured, simultaneously, with electrical conductivity and acoustic velocity and amplitude. Crack closure is also monitored for the fractured samples. All experimental control and data‐acquistion functions are performd by a microcomputer. A discussion of data‐analysis techniques and typical data are also presented.