Current status of technology for hydrogeological investigation, 1

In order to establish a hydrogeological model for a rock mass, data is required on its hydrogeological properties. A development for geophysical logging technique which is considered to be available for obtaining data on physical properties of rock mass is being carried out aiming at examination of its applicability to a hydrogeological evaluation of the rock mass with a assumption of correspondances between the hydrogeological and the physical properties of the rock mass. In the development of the technique, a borehole was drilled in a granitie rock, followed by measurements of physical parameters by geophysical loggings and laboratory tests on the drill cores and loggings. A consideration is being made on the relationship between the physical properties and the features of fractures and alterations which were obtained by the above methods. The results are as follows: (1) While electric and sonic loggings are found to be available for identification of fracture and alteration zones, micro-resistivity logging is for single fractures. (2) Density-neutron loggings may be useful for detection of fractures with water potentially. (3) The high porosity (φL) zones resulted from density-neutron loggings tend to correspond to fracture zones with alteration. (4) The high porosity (φSL) zones resulted from sonic logging are likely to correspond to those with high fracture densities regardless of alteration. (5) Division into three rock segments with depth based on the core logging was proved to be compatible with the results of the geophysical logging. Specifically, the features of fracture and alteration correlate with rock classification and proposity difference (|φL - φSL|) in each segment. (author)