WRRCTR No.21 Application of Electric Well Logging and Other Well Logging Methods in Hawaii

Abstract

In 1966, the Water Resources Research Center initiated a comprehensive study of electric well-logging and other geophysical well-logging techniques in Hawaii. The primary objectives of this study were to determine what results could be obtained by the use of conventional electric and geophysical well-logging methods under Hawaiian conditions and to collect as much basic geologic, hydrologic, and geometric information as possible from wells in Hawaiian aquifers. The functions logged include spontaneous potential, point resistivity, short and normal resistivity, lateral resistivity, water temperature, water conductivity, and caliper. Resistivity logging in Hawaii produced much important qualitative information and some quantitative information. Resistivity logs from wells in basaltic aquifers indicate the location, number, thickness, and total thicknesses of permeable and less permeable formations and are extremely 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. The logs also provide a direct measurement of depth to water, depth of casing, and depth of hole. Spontaneous potential logs sometimes are inconsistent and unreliable and are used primarily for correlation with other logs. Conductivity and temperature logs provide a direct quantitative measure of water conductivity and water temperature and provide considerable insight into the depth, thickness, quality, and temperature of waters contained in the wells of Hawaii. Borehole conductivity and temperature data also aid in the interpretation of the complex dynamic Ghyben-Herzberg lens relationships. The caliper module, which provides a measure of the well diameter, has been subject to frequent mechanical breakdown, however, recent alterations of the caliper module's design should allow the device to perform to its expected capability. Borehole photography employed recently by the Board of Water Supply provides positive identification of most Hawaiian rock types. Correlation between the photologs and electric logs is very good.