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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapte
r 3 – P ressure Transient Analysis (PTA) -p112/743
3.H.4
Basics
The simple analysis is based upon the study of the pressure and temperature differences
between two or more gauges placed in the test string at different depths. The figure below
shows schematically what happens to the pressure at the different sensors, if a ‘gas-oil’
interface is moving downwards and passes the sensors.
Fig. 3.H.2 – Fluid movement downwards
The example assumes that any background behavior is following a constant transient (trend)
or is in Pseudo-Steady state (PSS).
Once the gas-oil interface hits the upper sensor, the pressure at this sensing point remains
‘constant’ while the interface moves towards the lower pressure point.
The pressure at the lower sensor declines linearly if the fluid interface movement is constant.
It becomes constant again after the interface has moved below the lower pressure sensor. The
difference in pressure between the two sensing points is represented by the difference in fluid
gradient between oil and gas.
The following illustration represents the ‘difference channel’ between the two sensing points,
and by simple analysis it can be determined what fluid phase changes have caused the
observed phenomenon (see QA/QC).