Pressure log-log plot of unit-rate drawdown survey pressure drop  $//<![CDATA[ \begin{array}{l}\delta p(t) = p_{wf}(0) - p_{wf}(t)\end{array} //]]>$ and pressure log-derivative  $//<![CDATA[ \begin{array}{l}\displaystyle p'(t) = t \, \frac{d p_{wf}}{d t}\end{array} //]]>$ (see examples at Fig. 1 – Fig. 3).

Traditionally the pressure drop on pressure log-log plots is denoted by  $//<![CDATA[ \begin{array}{l}p(t)\end{array} //]]>$ which is the same as  $//<![CDATA[ \begin{array}{l}\delta p(t)\end{array} //]]>$:   $//<![CDATA[ \begin{array}{l}p(t) = \delta p(t)\end{array} //]]>$ but since it's a consistent practise it usually does not create a confusion among well test engineers. 

The pressure log-derivative  $//<![CDATA[ \begin{array}{l}p'(t)\end{array} //]]>$ provides a zoomed insight into the pressure diffusion dynamics at different times which helps identifying the pressure diffusion model behind the pressure variation.

See PTA Type Library for a wide range of typical PTA Diagnostic Plots.

The usual convention is to split pressure transient response in three major time intervals (see also Fig. 4):

See Also

Petroleum Industry / Upstream / Subsurface E&P Disciplines / Well Testing / Pressure Testing / Pressure Transient Analysis (PTA)

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