geometrical factor | Energy Glossary

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# geometrical factor

1. n. [Formation Evaluation]

The response of a logging measurement as a function of distance from the tool. The geometrical factor can be radial, reflecting the response perpendicular to the tool; vertical, reflecting the response along the tool axis; or two-dimensional, reflecting both. It can also be a differential geometrical factor, which is the contribution to the signal at a particular distance; or integrated, which is the sum of all signals from the tool to a particular distance. The term geometrical factor was introduced for induction logging since it gave a convenient method for computing the reading in a heterogeneous environment. For example, in an invaded formation the log reading, Clog, can be written as: Clog = Gi * Cxo + (1 - Gi) * Ct where Gi is the geometrical factor for a diameter of invasion Di, and Cxo and Ct are the conductivities of the invaded zone and the undisturbed zone. A true geometrical factor depends only on the geometry of the volume concerned, which in practice is only true for induction logs at zero conductivity. However, the term has come to be used for other cases and for other measurements even though the geometrical factor depends significantly on formation properties. The correct term for these cases is the pseudogeometrical factor.