Pressure difference between the current bottom-hole pressure $\begin{array}{l}p_{wf}(t)\end{array}$ and the bottom-hole 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 :

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

Pressure drop is:

positive	$\begin{array}{l}\delta p (t) >0\end{array}$	when production rate is increased or injection rate is decreased
negative	$\begin{array}{l}\delta p (t) < 0\end{array}$	when production rate is decreased or injection rate is increased

On log-log plots the pressure drop is always pictured as positive (see Fig. 1).


Fig. 1. Example of pressure drop P (in blue ) derived from them BHP data records (Fig. 2) and presented at log-log plot	Fig. 2. A source BHP data records which lead to a pressure drop on Fig. 1

In particular case when the well has been shut-in for a long time and bottom-hole 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:

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

as the initial bottom-hole pressure value $\begin{array}{l}p_{wf}(t_0)\end{array}$ represents formation pressure $\begin{array}{l}p_e\end{array}$ : $\begin{array}{l}p_{wf}(t_0) = p_e\end{array}$

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See Also

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Pressure Drop

See Also