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, C
_{log}, can be written as:
C
_{log} = G
_{i} * C
_{xo} + (1 - G
_{i}) * C
_{t}
where G
_{i} is the geometrical factor for a
diameter of invasion D
_{i}, and C
_{xo} and C
_{t} 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.