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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapte
r 3 – P ressure Transient Analysis (PTA) -p118/743
The below figure illustrates how the pressure at the sandface at early time can actually rise
above reservoir pressure. Imagine a well with a well head pressure A. The upper part of the
well is filled with a liquid/gas mixture of a certain weight and in the lower part of the well gas
is predominant (admittedly, a rather theoretical assumption). The gas phase at the bottom is
considered weightless. In between the two phases is a frictionless piston. The gauge pressure
at the bottom of the well is therefore the wellhead pressure plus the weight of the oil mixture,
A+P. Lets now assume that we turn this cylinder upside down, the wellhead pressure stays at
A+P and the bottom hole pressure increases to A+2P. This induces an abnormal rise in the
bottom hole gauge pressure that can be above reservoir pressure.
Fig. 3.I.7 – Gas humping
See the following figure that illustrates the hump caused by this phenomenon. This is a
classical feature in Pressure Transient Analysis.
Fig. 3.I.8 – Gas humping