Plotting BHP  $//<![CDATA[ \begin{array}{l}p_{wf}(t)\end{array} //]]>$ and formation pressure  $//<![CDATA[ \begin{array}{l}p_e(t)\end{array} //]]>$ vs cumulatives  $//<![CDATA[ \begin{array}{l}Q(t) = \int_0^t q_t(\tau) d\tau\end{array} //]]>$

It shows unit slope for PSS flow regime:

while  $//<![CDATA[ \begin{array}{l}p_{wf}(t)\end{array} //]]>$ and  $//<![CDATA[ \begin{array}{l}p_e(t)\end{array} //]]>$ are being parallel to each other.

The difference between two straight lines  $//<![CDATA[ \begin{array}{l}\Delta p = | p_e(t) - p_{wf}(t) | = \rm const\end{array} //]]>$ is related to productivity index $//<![CDATA[ \begin{array}{l}J\end{array} //]]>$ and flowrate $//<![CDATA[ \begin{array}{l}q_t\end{array} //]]>$ which stay constant during the PSS flow regime:

The increase/decrease in gap between parallel lines is indicating increase/decrease in productivity index  $//<![CDATA[ \begin{array}{l}J\end{array} //]]>$.

The increase/decrease of the parallel lines slope is indicating decrease/increase (inverse response) of the drainage volume.

Flattening out of parallel lines is indicating transition to Steady-State flow regime.

See Also

Petroleum Industry / Upstream /  Production / Subsurface Production / Field Study & Modelling / Production Analysis

0D Material Balance @model