Comparative performance of focused and normal devices through a numerical study

The superiority of focussed devices over traditional Normal devices has remained a controversy in geophysical literature. A two-dimensional finite-difference scheme for numerical modeling of Normal and Laterlog(LL7) is undertaken to clarify the matters concerned. Spacing for spacing, normal log is better than LL7 for e/AM>1 with R-s = R-m and R-t/R-m <= 500. Unlike the model tank experiment limitations (Roy & Appa Rao, 1976, 1978), in our numerical simulations, we could achieve perfect current focussing and evaluate the performance of existing alternate geometric factors due to Roy (1975) and Moran (1976). The computed R (a)/R (m) for LL7 was not even close to R (a)/R (m) under ideal conditions. But a simple two electrode device performs better in comparison to LL7 device provided AM= A(1) A(2). This assertion is valid even for dynamic current ratio settings also.