Automatic Computation of Schlumberger Apparent Resistivity Curves

Abstract

Geophysical prospecting by the apparent resistivity method involves the measurement oC apparent resisitvity between two potential electrodes as a Cunction oC the separation of two collinear current electrodes, From the .early days. of the application oC the resistivity sounding method, an important tool in the interpretation oC the data has been the comparison oC the apparent resistivity curves obtained from the field observations with apparent resistivity curves computed Cor assumed models of the layered earth consisting oC two or three horizontal, homogeneous, and isotropic layers oC given thickness and resistivity. Theoretical curves. Cor models of more than two or three layers are approximated using published nomograms .
A modified version oC the KoeCoed (1979) program Cor . the computation of the sample values oC the apparent resistivity and current electrode spacing alongwith resistivity transform hi a Schlumberger configuration, using the.linear filter method by Gosh (1971) is presented. This program has been written in Turbo BASIC language arid is based on the sampling Interval oC the Courth oC a decade. By the twoCold application oC the filter, the sampling values oC the apparent resistivity are computed at intervals oC an eighth oC a decade. In this trial and error method, the entire apparent resistivity curve oC a model layered structure is calculated Cor comparison with the measured curve