Influence of dry hole diameter in density γ-γ-logging

Abstract

In order to eliminate the influence of borehole diameter on the results of density γ‑γ logging, special spring‑loaded 2π probes are used. In small diameter wells (36‑50 mm) the use of spring‑loaded probes is difficult. Symmetrical 4π probes are widely used for such boreholes. However, the presence of an intermediate zone (air, water, drilling mud) between the probe and the borehole walls leads to a significant dependence of the 4π probe readings on the borehole diameter. When the borehole diameter is constant, this dependence can be taken into account when calibrating the probes. Violation of the identical conditions of calibration and measurement when the borehole diameter is changed leads to differences between the measured ρₘₑₐₛ and true ρₜᵣᵤₑ values of density.

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