Well flow regime with constant rate and constant delta pressure between wellbore and formation does not change in time:
(1) | q_t(t) = \rm const |
(2) | \Delta p(t) = | p_e(t) - p_{wf}(t) | = \Delta p = \rm const |
During the PSS regime the formation pressure declines linearly with time: p_e(t) \sim t.
The exact solution of diffusion equation for PSS:
| varying formation pressure at the external reservoir boundary | ||
| varying bottom-hole pressure | ||
| constant productivity index |
and develops a unit slope on PTA diagnostic plot and Material Balance diagnostic plot:
Fig. 1. PTA Diagnostic Plot for vertical well in single-layer homogeneous reservoir with impermeable circle boundary (PSS). Pressure is in blue and log-derivative is in red. |
See also
Steady State (SS) well flow regime