Study on Radial Investigation Depth Characteristics of Induction Logging on Heterogeneous Stratum

摘要

In induction logging, using geometrical factor to analyze radial investigation depth is a useful way to estimate the radial investigation ability of a logging tool. But radial investigation depth analysis based on DOLL geometrical factor often leads to substantial inaccurate estimates of the true apparent conductivity sain inhomogeneous or invaded ases. Although propagation effect geometrical factor (PEGF) includes both the mutual-effect of eddy flows and the reflection and transmission on the interface of heterogeneous media, it's too complicated to use.The advanced geometrical factor (AGF) discussed in this paper combines the merits of DOLL geometrical factor and propagation effect eometrical factor. The AGF considers the mutual-effect of eddy flows in nonhomogeneous medium and gives good predictions of two kinds of relations in an axisymmetric inhomogeneous two-layer media in a permissive error scale. One kind of the relations is between radial investigation depth and emission signal frequency. The other is the relation etween radial investigation depth and electrical resistivity ratio of invaded zone and original stratum. Different from usual way of making conclusions from graphs of experimental data, proof formulas and simulations are given in this paper. The conclusions referred to the radial investigation depth characteristics using the Doll GF are compensated y using AGF.