WellCAD Basics - Advanced Logic Technology

1.5.11 Correcting Data for Borehole Conditions
BOOK 1 - WELLCAD BASICS - 145
Several factors such as borehole size or the presence of casing influence the
recording of count rates and the amount of registered events. In addition the deadtime
of the detector system must be taken into account and the counts corrected
before interpreting / calibrating the data.
The Common > Process > Borehole Condition Correction process has been
designed for total gamma and spectral gamma measurements but can also be applied
to other types of measurements (e.g. to correct density or neutron data).
Log: Select the log (Well, Mud, Interval or FWS Log) containing the data to be
corrected.
Dead Time: The dead-time of a detector is the short period following the detection
of a count or pulse, during which no other counts can be detected. It is a recovery
period of the crystal or tube. Knowing the dead-time t of the measurement system
the corrected count rate N can be computed from the measured count rate n:
N = n / (1 – nt)
(see Serra, O. & L., 2004, “Well Logging – Data Acquisition and Applications”, Serra Log)
Check the Dead Time option and enter the dead time in microseconds if you
would like to correct your data.
Correction Factors: Counting rates are attenuated to different degrees by hole-fluid
and any mud cake, tubing, casing, cement, decentralization of the tool etc. that may
be present. Correction charts providing factors or equations to compute correction
values are available from tool manufacturers. In order to apply a series of different
factors over defined depth intervals you can extend the Correction Factors list
control: