Pressure Drop

Pressure difference between the current wellbore flowing pressure $\begin{array}{l}p_{wf}\end{array}$ and the wellbore flowing pressure $\begin{array}{l}p_{wf}(t_0)\end{array}$ at time moment $\begin{array}{l}t=t_0\end{array}$ when flowrate has changed :

$\begin{array}{l}\displaystyle \delta p (t) = p_{wf}(t_0) - p_{wf}(t)\end{array}$

Fig. 1. A sample of typical DTR (pressure drop P in blue and log-derivative P' in red) presented in log-log coordinates for PTA type-library analysis

In particular case when the well has been shut-in for a long time and wellbore pressure has stabilised by the time moment $\begin{array}{l}t_0\end{array}$ and when well is opened for flow the pressure drop will be equal to pressure drawdown:

$\begin{array}{l}\displaystyle \Delta p(t) = p_e - p_{wf}(t) = p_{wf}(t_0) - p_{wf}(t) = \delta p (t)\end{array}$

as the initial wellbore pressure point represent formation pressure $\begin{array}{l}p_e\end{array}$ :

$\begin{array}{l}\displaystyle p_{wf}(t_0) = p_e\end{array}$

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Pressure Drop