ELECTRIC LOGGING APPLIED TO GROUND‐WATER EXPLORATION

Abstract

A method is described for the determination of the quality of ground water in granular aquifers penetrated by rotary‐drilled holes electrically logged. Conventional techniques of electric‐log interpretation, to determine true bed resistivity from apparent resistivity values, are briefly described; and a method for converting water‐resistivity values into hypothetical chemical analyses is explained. The objective of the method is to narrow the limits of error in quality‐of‐water estimates based upon electric logs. Water‐well contractors are fully aware of the risks attendant in making drill‐stem tests in open hole, which is the method now employed to obtain representative samples of formation water. Packer failure results in contaminated samples; hole collapse may mean loss of drill stem, screen, and the hole. In the Gulf Coast where water‐well tests range in depth from 100 to 3,000 feet, methods that will eliminate at least a part of the need for drill‐stem tests deserve consideration. The paper deals also with methods of determining formation porosity in situ, which is an important factor in salt‐water‐encroachment problems.