MMIJ Annual Meeting

Permeability to gas or water is recognized as the main physical property of rocks for controlling fluid flow. Near fault zones where macroscopic fractures exist, in addition to the micro-fracture rock matrix, the fluid flow paths are complicated and the structures are heterogenous. Although there are many methods for testing rock permeability, the methods suffer from compromise between accuracy, detection limits at low range of permeability, sample volume, time, and cost. In addition, the fluid flow paths must be mapped at small and large scale. The amount of information that is present in drill core is often not utilized completely. At Kyoto University, with collaboration of McGill University (Canada), we developed a new practical N₂ gas pressure-decay test method that is useful for routine and accurate testing of rocks of a wide permeability range (10^-19 m² to > 10^-8 m², or more than 10 orders of magnitude effective instrument detection limits). A new seal method using epoxy rings, in addition to probe rubber tip seals, allows to test a wide range of permeability and eliminates gas leaks at the probe-rock contact. The penetrative macropore networks were directly observed from gas discharge patterns on drill core surfaces. The method also provides a direct observation and mapping of fluid flow paths in both the porous rock matrix (e.g. hydrothermally altered granite, sandstone) and in fracture channels in fracture networks that exist in extracted drill core. We demonstrate this on three types of granite from the Tsukiyoshi fault zone (Mizunami site, Gifu, Japan), and from the transects at depth of a major fault zone below the Athabasca Basin, north-central Canada. Such routine, rapid, and accurate testing of rock permeability, together with the mapping of actual fluid flow paths and types of connected macro-porosity, can provide new insights into present- and paleo-fluid flow in natural resource sites of interest.