1.
n. [Formation Evaluation]
With reference to
invasion, an abrupt change from the flushed zone to the undisturbed zone, with no
transition zone or
annulus. This simple
model is used most commonly in connection with older
resistivity logs since it allows the invasion to be represented by three parameters: flushed-zone resistivity, undisturbed-zone resistivity and diameter of invasion. The model assumes equal invasion at all azimuths. Newer
array logs allow more complex invasion models to be interpreted.