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The wellbore Wellbore flow is called stabilised if the delta pressure across wellbore is not changing over time.
The formation Reservoir flow is called stabilised if the well productivity index is not changing over time.
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It's important to remember the difference between constant rate formation flow and stabilised formation reservoir flow.
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The stabilised formation flow may go through a gradually changing flow rate due to formation pressure change, while the productivity index stays constant.
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The table below is summarizing the major differences between SS and PSS regimes.
| Steady state regime (SS) | Pseudo-steady state (PSS) | ||||||
|---|---|---|---|---|---|---|---|
| Boundary | Full pressure support | No pressure support | |||||
| Productivity index (PI) |
| constant | constant | ||||
| Flowrate |
| constant | constant | ||||
| constant | constant | |||||
| Botomhole pressure (BHP) |
| constant | varying | ||||
| Formation pressure |
| constant | varying |
It's again important to avoid confusion between the termines stationary conditions (which mean that refered properties are not chaning in time) and stabilised flow conditions which may admit pressure and rate vraition.
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