Electric Well Logging of Hawaiian Basaltic Aquifers

An extensive program of electric well logging has been conducted in Hawaii during the past three years to determine the applicability of this tool to the volcanic environment which exists in Hawaii. Electric well logging techniques were found to be useful in Hawaiian basaltic aquifers; however interpretation of both spontaneous potential logs and resistivity logs varies from the conventional interpretation of electric logs in sediments. The interpretation of fluid conductivity logs in Hawaii follows conventional water well techniques. The analysis of spontaneous potential and resistivity well logging in basalts, which constitute most of the Hawaiian aquifers, poses problems because of the relatively uniform composition of the basalts and the complex relation of porosity to resistivity in basaltic aquifers, and because logging usually is performed in water‐filled boreholes. Spontaneous potentials are thought to result primarily from fluid flow rather than from electrochemical potential, and positive SPs generally indicate zones with flow from the aquifers into the well, and negative SPs generally indicate zones with little flow or flow from the well into the aquifer. Resistivity logs indicate the location, number, individual thickness, and total thicknesses of permeable and less permeable formations, and are useful as indicators of water‐yielding zones. High resistivities generally are indicative of dense impermeable basalts and low resistivities are indicative of porous permeable zones most likely to contribute water to the borehole. Both resistivity and spontaneous potential logs provide a direct measurement of depth to water, depth of casing, and depth of hole.