Exploration Geophysics - Volume 5, Issue 2, 1974

The Pole-Multidipole method is presented as a practical alternative to the Schlumberger method of geoelectrical sounding. Its electrode array is asymmetrical and uses only one mobile electrode. A multiplicity of potential-electrodes ensures optimal sampling of the local potential distribution and guarantees reliable field data. Current- and potential-electrode effects on apparent resistivity curves are also monitored. A consideration of the theoretical and practical aspects of the method indicates that the interpretation procedures of the Schlumberger method may be retained.

The resistivity and I.P. responses of a large number of conventional electrode arrays in two distinct geological environments have been simulated by digital computer. Numerical calculations are based on a method of using surface integral equations which is suitable for micro, mini and mainframe computers. This procedure allows array responses of adequate accuracy to be calculated at a fraction of the cost of other numerical methods and makes a comprehensive evaluation of electrode arrays in complex situations feasible.

The results of the study show that the commonly used electrode arrays exhibit a variety of response characteristics. These features essentially reflect the differing “geometric couplings” of the arrays with the three-dimensional models treated. In certain situations enhancement of deeper bodies takes place indicating that optimum geometric coupling with the environment has been achieved. In these cases the most diagnostic anomalies usually result.

The study concludes that if initial effort is expended in the design of optimum electrode arrays and field procedures the most diagnostic information will be obtained. This information, combined with the ease and flexibility of the computer modelling procedures described in this paper, provide the geophysicist with a powerful tool for the planning of resistivity and I.P. field surveys and their subsequent interpretation.