Basic HTML Version
Ecrin v4.12 - Doc v4.12.02 - © KAPPA 1988-2009
Saphir Guided Session #5
•
SapGS05 - 3/6
C01.1 • QAQC
The principle used by Saphir is basically the study of the changes in hydrostatic head between
gauge sensing points. This is achieved by taking the difference between a reference pressure
(gauge) and the other gauges. Any change in the pressure difference will indicate a change in
the fluid phase between sensing points, thus indicating pressure sequences that are dominated
by wellbore effects rather than the reservoir signal. The absolute difference will also indicate
the quality of the tools used for the pressure and temperature recordings since the anticipated
pressure difference can be estimated as long as you know the depth difference and expected
fluid gravity in the well. Therefore the absolute value difference can be estimated between the
individual tools and a quality indicator assigned.
Other anomalies such as sudden value shifts and drift can easily be detected and the more
suspect tools can be eliminated from the pressure transient analysis.
The usual difference convention is to take the difference between the lowest gauge in the well
and those above, thus forcing the pressure difference to show an increase in fluid density when
the difference increases and a decrease of density when the difference decreases.
In our case the anticipated difference between Gauge 1 and 4 and Gauge 2 and 3 can be
estimated from the depth difference of 23 ft with a fluid gradient 0.34 psi/ft which amounts to
some 8 psi.
C01.2 • Generating the difference channel and analysis
Click on the difference
icon and declare Gauge 1 (‘SapGS05_1’) as the reference gauge
as this (and Gauge 4) is the lowest gauge. Accept other defaults. The difference channels are
generated automatically but because of the spikes in the pressure difference the scale is much
too coarse to see any trend or to make any qualitative analysis. These spikes are caused by a
de-synchronization in time between the gauges. Figure C01.3.
Fig. C01.3 • QAQC after first generation of difference