WellCAD Basics - Advanced Logic Technology

BOOK 1 - WELLCAD BASICS - 153
Input Channels:
Select the appropriate input channels from the drop down lists. Well and Mud Logs
are listed.
1.5.13 Spectral Gamma Processing
Data from spectral gamma tools can either be imported into WellCAD using the
*.TFD file import, a special file format output by the MATRIX logging system, or
loaded from an ASCII file. The spectrum data should be imported into a FWS Log
type in order to allow a spectrum display and support the conversion of counts to
energy.
A number of processes have been implemented to work with spectrum data. These
processes are explained in the following paragraphs and can be accessed from the
Process > Spectral Gamma menu.
1.5.13.1 Stack Spectra
Gamma ray emission is a random process and count rates generally vary about a
mean value. Counts must be accumulated over a period of time and averaged in
order to obtain a reasonable estimate of the mean.
The Stack Spectra process creates a new FWS Log containing at each depth or time
sample an average spectrum computed from the actual trace, the N/2 traces
preceding and the N/2 traces succeeding the actual trace. N corresponds to the
number of stacks and must be entered by the user. The following figure illustrates
the principle of the Stack Spectra process.
N / 2 Trace
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Actual Trace N + 1 traces � Average Trace
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N / 2 Trace
E.g. the process can be applied to a static measurement, where the spectral gamma
probe was held over a certain time at a constant depth in the center of an enriched
zone within a calibration pit. The stacking rate should be chosen high enough to