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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 productivity index maybe still in transition after the last rate change.

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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• Stabilised reservoir flow which may happen during pressure variation.

See Also

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Physics / Mechanics / Continuum mechanics / Fluid Mechanics / Fluid Dynamics