“Scale modelling of the laterolog using synthetic focusing methods,” The Log Analyst, Vol. 28, No. 4, pp. 357-369, July-August 1987.
A scale model of a Shallow Laterolog tool has been constructed and tested. The Laterolog tool is a focused electrode tool used in well logging for the measurement of formation resistivity. The model tool is scaled down by approximately 20 to 1, and makes use of one of two alternative methods of focusing the current into the formation. One method, called manual focusing, is a manual analog to the focusing method used in the actual tool. The other method, called synthetic focusing, uses the principle of superposition to analytically simulate a focusing situation. This method requires the measurement of electrode potentials for separately applied currents. Both methods are used to log a synthetic formation composed of porous concrete suspended in saline water, and the logs obtained are equivalent. The formation boundaries are well defined and the measured bed resistivity is close to the true value and to the value calculated with a finite element program. The synthetic method is simple to apply, and avoids the potentially unstable feedback amplifier used in full scale tools.