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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapte
r 3 – P ressure Transient Analysis (PTA) -p111/743
3.H.3
The concept of Differential Pressure Analysis
The analysis is based upon the difference in pressure measured between tandem pressure
gauges, the simplest case, or a combination of pressure differences if multiple gauges are used
during a pressure survey.
The study of these differences can reveal the following problems and has a direct impact on
the choice of the data measurements for a valid PTA:
Detect phase segregation in the wellbore;
Establish phases for pressure correction;
Indentify the movement of the fluid interface movements (water / oil / gas);
Identify temperature anomalies or other gauge technical problems;
Check the gauge accuracy and resolution;
Identify gauge drift;
Other technical or electronic malfunctions;
Selection of the most representative data channel, if any.
By convention the pressure difference between gauges is calculated so that that an increase in
the ‘difference channel’ represents an increase in the fluid density between the gauges sensing
points, and a decrease a reduction of the fluid density, i.e.:
p
=
p
lower
-
p
upper
The ‘difference channel’ behaviour is the same whatever the gauge offset. The upper gauge
may well read a higher pressure than the lower gauge, possibly due to a gauge problem or just
because of accuracy, but the ‘difference channel’ would have the same identifiable shape.
Fig. 3.H.1 – Difference channel