A boundary dominated Reservoir flow with well around the well with well productivity index is not changing over time.
It's important to remember the difference between constant rate formation flow and stabilised reservoir flow.
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J(t) = J = \rm const |
There should be no confusion between stabilised reservoir flow and constant-rate production.
Constant-rate production may not represent stabilised reservoir flow as Anchor
On the other hand, a stabilised reservoir flow may go through a gradually changing flow rate due to formation pressure change with productivity index staying constant.
The WFP methods are not applicable if the well flow is not stabilised even if the flow rate is maintained constant.
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There are two special reservoir flow regimes which are both stabilised and maintain constant flow rate: steady state regime
and
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The steady state regime Steady State flow regime (SS) regime is is reached when the flow is stabilised with the full pressure support at the external boundary.
The pseudoPseudo-steady state State flow regime (PSS) regime is is reached when the flow is stabilised with with no pressure support at the external boundary.
In both above cases, the drawdown and flow rate will stay constant upon productivity stabilisation.
As for formation The formation pressure
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The table below is summarizing summarising the major differences between SS and PSS regimes.
Steady state regime (SS) | Pseudo-steady state (PSS) | ||||||
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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 term:
- Stationary ( or Steady State) reservoir flow, which means that all dynamic properties are not
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- changing in time
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- ,
and
- Stabilised reservoir flow which may happen during pressure variation.
See Also
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Physics / Mechanics / Continuum mechanics / Fluid Mechanics / Fluid Dynamics