POROSITY AND PATHWAY DETERMINATION IN CRYSTALLINE ROCK BY POSITRON EMISSION TOMOGRAPHY AND NEUTRON RADIOGRAPHY

This study demonstrates that positron emission tomography (PET) and ne utron radiography (NR) techniques are complementary methods for determ ining the fluid pathway and porosity in crystalline rock. After prelim inary injection of an organic solvent (e.g. isopropanol) front followe d by the injection of the polymer solution (e.g. epoxy used for both t echniques) and resin hardening, rock cutting may be performed. Flow pa thway may be imaged by using a beta(+) emitter (e.g. Ga-68) in the res in. With a high-resolution PET camera, determination of the original w ater carrier features is possible in granodiorite pieces 20 cm in size and in simulated features with porosities of the order of 0.2. The us e of a beta(+) tracer and the camera field, however, limit the lateral resolution of the technique (10 mm). Neutron radiography makes it pos sible to visualize the simulated porous phases by neutron transmission . The transmission process depends on the neutron scattering propertie s of the hydrogen-rich material (e.g. epoxy resin). Combination of 2D pictures may rebuild the 3D pattern. Lateral resolution may be in the range of 1 mm; however, the thickness of the rock sample must not exce ed 10 cm. Complementarity of these techniques is discussed and they ar e compared with other methods used to determine porosity.