Structural, hydraulic, and geophysical properties of granite near Oracle, Arizona

Abstract

A combination of geophysical and hydraulic testing was conducted in granite near Oracle, Arizona. The purpose of the work is to determine relationships, if any, among fracture distribution, geophysical, and hydraulic properties of low permeability fractured rock. Neutron, gamma, acoustic velocity, electrical resistivity, and acoustic televiewer logs, and the results of over 100 single-hole straddle-packer injection tests were used to describe the fracture system. The geophysical techniques are sensitive to both subtle variations of the granite and to the fracture network. Fracture densities determined by the acoustic televiewer over hydraulically tested intervals do not correlate with measured hydraulic conductivities for the intervals. However, a strong correlation was noted between the neutron log response and measured hydraulic conductivities and used to estimate hydraulic conductivity in areas that were not hydraulically tested. A map of hydraulic conductivity was also constructed using the geostatistical technique of kriging.