pseudogeometrical factor | Energy Glossary

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# pseudogeometrical factor

1. n. [Formation Evaluation]

The response of a logging measurement as a function of distance from the tool. The pseudogeometrical factor is normally radial, reflecting the response perpendicular to the tool. It can be a differential factor, which is the contribution to the signal at a particular distance, but is more normally integrated, which is the sum of all signals from the tool to a particular distance. The pseudogeometrical factor developed from the concept of the geometrical factor, and is expressed in the same way. For example, for a radial distance x from the tool, the integrated radial pseudogeometrical factor, Jx, can be written as: Jx = (Ux - Ut) / (Uxo - Ut) where Ut is the log reading of the undisturbed zone (or, alternatively, the reading with no invasion), Uxo is the log reading of the flushed zone (or, alternatively, the reading with infinite invasion), and Ux is the log reading with a step profile invasion to depth x. Unlike the geometrical factor, Jx depends on the values of both Uxo and Ut. Pseudogeometrical factors are a useful way to express the radial response (or vertical response) in typical conditions. The physics of each measurement determines how much Jx varies with Uxo and Ut. Pseudogeometrical factors are often used to express the response of nuclear and resistivity logs, but are not appropriate for acoustic and electromagnetic propagation logs (where the response is too dependent on the contrast in properties), or nuclear magnetic resonance logs (where the response is too localized).