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11.2.4 The characteristic form of the diagram recorded during
Measuring the bottom hole and formation pressure and
the general principle of its decoding

In most problems of productive formation researches the data of

bottom hole P and formation pressure P form magnitudes are used.
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The bottom hole pressure is measured in the running well (well in

operation). The formation pressure is measured in the stopped wells or
the wells which are not in operation in the same way as the bottom
hole one. Using downhole pressure gages in most of cases the bottom
hole and formation pressures are measured during one device running.

Downhole pressure gage is put down to the point of the measuring,
then it is kept for 15 – 25 minutes to record the bottom hole pressure
and after this the side (flow-line) Christmas-tree gate valve is shut (the

well is stopped) and the device records the pressure-build-up curve
(for determining the formation pressure).
The diagram recorded during measuring the bottomhole and

formation pressure is given in fig. 11.2.
The measured pressure in the scale of the blank is read from zero

line 00'. The line СD characterizes the increase of the pressure which
is recorded by the downhole pressure gage while it is put down into
the well. On the line DЕ (after keeping the downhole pressure gage in
the bottom for 15 – 25 minutes) the bottom hole pressure is recorded.
Point Е corresponds tothe moment of shutting the side (flow-line)

Christmas-tree gate valve. After this moment of time downhole

pressure gage records the pressure-build-up curve that is the line ЕF.
On the line FG the pressure goes down due to the downhole pressure
gage lifting up.

To decode the diagram shown in fig. 11.2 that is to measure the

ordinates (P) the special reading devices such as the field comparators,
laboratory comparators, instrumental microscopes and others are used.
One of the devices for decoding the pressure records is the field
comparator K-7. It consists of micrometer (microscrew), vernier,

transverse and lengthwise measuring rulers and magnifying glass. The
laboratory comparators are more accurate than the field ones. In
particular, the error of the laboratory comparator K-9 is not bigger

than ± 0.01 mm.

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