Abstract
This report presents a newly developed gas-medium tri-axial testing system capable of performing permeability test of rocks at effective pressures to 180 MPa, corresponding to the depth of about 10 km. Two permeability testing methods using the system, the oscillating pore pressure method and the gas flow method, were described for the case of using nitrogen gas as a pore fluid. The oscillating pore pressure method has been used to test permeability of the Kakegawa Group siltstone. The test results are summarized as : (1) Permeability of the Kakegawa Group siltstone generally decreased gradually with increasing effective pressure ; (2) In most cases the decreased permeability during the pressure increased period were not recovered to the initial value with depressurization ; (3) Each trend of the permeability reduction against the effective pressure change was almost similar to each other, while the overall permeability level of the each curve was different ; (4) Difference of the initial porosity of the specimen seemed to be responsible for the observed difference of the overall permeability level, and (5) Permeability of the sample became to be almost independent to the initial porosity at higher effective pressure more than about 100 MPa.
