It shows unit slope for PSS flow regime:

p_{wf}(t) = p_i - J^{-1} q_t - \frac{1}{ V_{\phi} \, c_t} Q(t)

p_e(t) = p_i - \frac{1}{ V_{\phi} \, c_t} Q(t)

while and are being parallel to each other.

The difference between two straight lines is related to productivity index and flowrate which stay constant during the PSS flow regime:

J = \frac{q_t}{\Delta p} = \rm const

The increase/decrease in gap between parallel lines is indicating increase/decrease in productivity index .

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